<PAGE>
 
                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                   FORM 10-K/A

(Mark One)
[ X ]            ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 (d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended     December 30, 2000

OR

[   ]         TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 (d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

              For the transition period from ..........to..........

                         Commission file number: 1-14092

                          THE BOSTON BEER COMPANY, INC.
             (Exact name of registrant as specified in its charter)

         Massachusetts                                04-3284048
(State or other jurisdiction of          (I.R.S. Employer Identification No.)
 incorporation or organization)

                   75 Arlington Street, Boston, Massachusetts
                    (Address of principal executive offices)
                                      02116
                                   (Zip Code)

                                 (617) 368-5000
              (Registrant's telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

      Title of each class              Name of each exchange on which registered
Class A Common Stock...............              NYSE................

        Securities registered pursuant to Section 12(g) of the Act: None


Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days. Yes  X    No
                                       ---      ---

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulations S-K is not contained herein, and will not be contained, to the
best of the registrant's knowledge, in definitive proxy or information
statements incorporated by reference in Part III of this Form 10-K or any
amendment to this Form 10-K. [X]

The aggregate market value of the Class A Common Stock ($.01 par value) held by
non-affiliates of the Registrant totaled $121,728,308 (based on the average
price of the Company's Class A Common Stock on the New York Stock Exchange on
March 7, 2001). All of the Registrant's Class B Common Stock ($.01 par value) is
held by an affiliate.

As of March 7, 2001 there were 12,370,763 shares outstanding of the Company's
Class A Common Stock ($.01 par value) and 4,107,355 shares outstanding of the
Company's Class B Common Stock ($.01 par value).

                       DOCUMENTS INCORPORATED BY REFERENCE

Certain parts of the Registrant's definitive Proxy Statement for its 2001 Annual
Meeting to be held on May 22, 2001 are incorporated by reference into Part III
of this report.

<PAGE>
 
                AMENDMENT NO. 1 TO THE BOSTON BEER COMPANY, INC.
                FORM 10-K FOR THE PERIOD ENDED DECEMBER 30, 2000

The Registrant hereby amends its Annual Report on Form 10-K for the year ended
December 30, 2000, by filing herewith the complete text of ITEM 14 of Part IV
thereof consisting of:



PART IV.
                                                                      Page

 Item 14. Exhibits, Financial Statement Schedules 
          and Reports on Form 8-K                                     3-6

                                       2

<PAGE>
 
                                     PART IV

Item 14. Exhibits, Financial Statement Schedules, and Reports on Form 8-K

     (a)  The financial statements and financial statement schedules are
          contained in Item 8 of Part II to this report on Form 10-K.

     (b)  During the fourth quarter of the fiscal year ended December 30, 2000,
          the Registrant filed no Current Reports on Form 8-K.

     (c)  Exhibits

     The following is a list of exhibits filed as part of this Form 10-K:

     Exhibit No.                Title
     -----------                -----

        3.1     Amended and Restated By-Laws of the Company, dated June 2, 1998
                (incorporated by reference to Exhibit 3.5 to the Company's Form
                10-Q filed on August 10, 1998).

        3.2     Restated Articles of Organization of the Company, dated July 21,
                1998 (incorporated by reference to Exhibit 3.6 to the Company's
                Form 10-Q filed on August 10, 1998).

        4.1     Form of Class A Common Stock Certificate (incorporated by
                reference to Exhibit 4.1 to the Company's Registration Statement
                No. 33-96164).

        10.1    Revolving Credit Agreement between Fleet Bank of Massachusetts,
                N.A. and Boston Beer Company Limited Partnership (the
                "Partnership"), dated as of May 2, 1995 (incorporated by
                reference to Exhibit 10.1 to the Company's Registration
                Statement No. 33-96162).

        10.2    Loan Security and Trust Agreement, dated October 1, 1987, among
                Massachusetts Industrial Finance Agency, the Partnership and The
                First National Bank of Boston, as Trustee, as amended
                (incorporated by reference to Exhibit 10.2 to the Company's
                Registration Statement No. 33-96164).



     Exhibit No.                Title
     -----------                -----

        10.3    Deferred Compensation Agreement between the Partnership and
                Alfred W. Rossow, Jr., effective December 1, 1992 (incorporated
                by reference to Exhibit 10.3 to the Company's Registration
                Statement No. 33-96162).

        10.4    The Boston Beer Company, Inc. Employee Equity Incentive Plan, as
                adopted effective November 20, 1995 and amended effective
                February 23, 1996 (incorporated by reference to Exhibit 4.1 to
                the Company's Registration Statement No. 333-1798).

        10.5    Form of Employment Agreement between the Partnership and
                employees (incorporated by reference to Exhibit 10.5 to the
                Company's Registration Statement No. 33-96162).

        10.6    Services Agreement between The Boston Beer Company, Inc. and
                Chemical Mellon Shareholder Services, dated as of October 27,
                1995 (incorporated by reference to the Company's Form 10-K,
                filed on April 1, 1996).

        10.7    Form of Indemnification Agreement between the Partnership and
                certain employees and Advisory Committee members (incorporated
                by reference to Exhibit 10.7 to the Company's Registration
                Statement No. 33-96162).

        10.8    Stockholder Rights Agreement, dated as of December, 1995, among
                The Boston Beer Company, Inc. and the initial Stockholders
                (incorporated by reference to the Company's Form 10-K, filed on
                April 1, 1996)

                                       3

<PAGE>
 
        +10.10  Agreement between Boston Brewing Company, Inc. and The Stroh
                Brewery Company, dated as of January 31, 1994 (incorporated by
                reference to Exhibit 10.9 to the Company's Registration
                Statement No. 33-96164).

        +10.11  Agreement between Boston Brewing Company, Inc. and the Genesee
                Brewing Company, dated as of July 25, 1995 (incorporated by
                reference to Exhibit 10.10 to the Company's Registration
                Statement No. 33-96164).

        +10.12  Amended and Restated Agreement between Pittsburgh Brewing
                Company and Boston Brewing Company, Inc. dated as of February
                28, 1989 (incorporated by reference to Exhibit 10.11 to the
                Company's Registration Statement No. 33-96164).

        10.13   Amendment to Amended and Restated Agreement between Pittsburgh
                Brewing Company, Boston Brewing Company, Inc., and G. Heileman
                Brewing Company, Inc., dated December 13, 1989 (incorporated by
                reference to Exhibit 10.12 to the Company's Registration
                Statement No. 33-96162).

        +10.14  Second Amendment to Amended and Restated Agreement between
                Pittsburgh Brewing Company and Boston Brewing Company, Inc.
                dated as of August 3, 1992 (incorporated by reference to Exhibit
                10.13 to the Company's Registration Statement No. 33-96164).

        +10.15  Third Amendment to Amended and Restated Agreement between
                Pittsburgh Brewing Company and Boston Brewing Company, Inc.
                dated December 1,1994 (incorporated by reference to Exhibit
                10.14 to the Company's Registration Statement No. 33-96164).

        10.16   Fourth Amendment to Amended and Restated Agreement between
                Pittsburgh Brewing Company and Boston Brewing Company, Inc.
                dated as of April 7,1995 (incorporated by reference to Exhibit
                10.15 to the Company's Registration Statement No. 33-96162).

        +10.17  Letter Agreement between Boston Beer Company Limited Partnership
                and Joseph E. Seagram & Sons, Inc. (incorporated by reference to
                Exhibit 10.16 to the Company's Registration Statement No.
                33-96162).

        10.18   Services Agreement and Fee Schedule of Mellon Bank, N.A. Escrow
                Agent Services for The Boston Beer Company, Inc. dated as of
                October 27, 1995 (incorporated by reference to Exhibit 10.17 to
                the Company's Registration Statement No. 33-96164).

     Exhibit No.                Title
     -----------                -----


        10.19   Amendment to Revolving Credit Agreement between Fleet Bank of
                Massachusetts, N.A. and the Partnership (incorporated by
                reference to Exhibit 10.18 to the Company's Registration
                Statement No. 33-96164).

        10.20   1996 Stock Option Plan for Non-Employee Directors (incorporated
                by reference to the Company's Form 10-K, filed on March 27,
                1998).

        +10.21  Production Agreement between The Stroh Brewery Company and
                Boston Beer Company Limited Partnership, dated January 14, 1997
                (incorporated by reference to the Company's Form 10-K, filed on
                March 27, 1998).

        +10.22  Letter Agreement between The Stroh Brewery Company and Boston
                Beer Company Limited Partnership, dated January 14, 1997
                (incorporated by reference to the Company's Form 10-K, filed on
                March 27, 1998).

        +10.23  Agreement between Boston Beer Company Limited Partnership and
                The Schoenling Brewing Company, dated May 22, 1996 (incorporated
                by reference to the Company's Form 10-K, filed on March 27,
                1998).

        10.24   Revolving Credit Agreement between Fleet Bank of Massachusetts,
                N.A. and The Boston Beer Company, Inc., dated as of March 21,
                1997 (incorporated by reference to the Company's Form 10-Q,
                filed on May 12, 1997).

                                       4

<PAGE>
 
          +10.25    Amended and Restated Agreement between Boston Brewing
                    Company, Inc. and the Genesee Brewing Company, Inc. dated
                    April 30, 1997 (incorporated by reference to the Company's
                    Form 10-Q, filed on August 11, 1997).

          +10.26    Fifth Amendment, dated December 31, 1997, to Amended and
                    Restated Agreement between Pittsburgh Brewing Company and
                    Boston Brewing Company, Inc. (incorporated by reference to
                    the Company's Form 10-K, filed on March 27, 1998).

          10.27     Extension letters, dated August 19, 1997, November 19, 1997,
                    December 19, 1997, January 22, 1998, February 25, 1998 and
                    March 11, 1998 between The Stroh Brewery Company and Boston
                    Brewing Company, Inc. (incorporated by reference to the
                    Company's Form 10-K, filed on March 27, 1998).

          +10.28    Employee Equity Incentive Plan, as amended and effective on
                    December 19, 1997 (incorporated by reference to the
                    Company's Form 10-K, filed on March 27, 1998)

          +10.29    1996 Stock Option Plan for Non-Employee Directors, as
                    amended and effective on December 19, 1997 (incorporated by
                    reference to the Company's Form 10-K, filed March 27, 1998)

          +10.30    Glass Supply Agreement between The Boston Beer Company and
                    Owens' Brockway Glass Container Inc., dated April 30, 1998
                    (incorporated by reference to the Company's Form 10-Q, filed
                    on August 10, 1998).

          10.31     Extension letters dated April 13, 1998, April 27, 1998, June
                    11, 1998, June 25, 1998 and July 20, 1998 between The Stroh
                    Brewery Company and Boston Brewing Company, Inc.
                    (incorporated by reference to the Company's Form 10-Q, filed
                    on August 10, 1998).

          10.32     Extension letters dated July 31, 1998, August 28, 1998,
                    September 28, 1998, October 13, 1998, October 20, 1998 and
                    October 23, 1998 between The Stroh Brewery Company and
                    Boston Brewing Company, Inc. (incorporated by reference to
                    the Company's Form 10-Q, filed on November 4, 1998).

          +10.33    Amended and Restated Production Agreement between The Stroh
                    Brewery Company and Boston Beer Company Limited Partnership,
                    dated November 1, 1998 (incorporated by reference to the
                    Company's Form 10-K, filed on March 25, 1999).


       Exhibit No.                Title
       -----------                -----


          10.34     Agreement between Boston Beer Company Limited Partnership,
                    Pabst Brewing Company and Miller Brewing Company, dated
                    February 5, 1999 (incorporated by reference to the Company's
                    Form 10-K, filed on March 25, 1999).

          10.35     Amendment to Revolving Credit Agreement between Fleet Bank
                    of Massachusetts, N.A. and The Boston Beer Company, Inc.,
                    dated March 30, 1999 (incorporated by reference to the
                    Company's Form 10-Q, filed on May 10, 1999).

          +10.36    Agreement between Boston Beer Company Limited Partnership
                    and Landstar Logistics and Transportation, dated January 9,
                    1999 (incorporated by reference to the Company's Form 10-Q,
                    filed on May 10, 1999).

          **+10.37  Consent to Assignment of the Amended and Restated Agreement
                    between Boston Brewing Company, Inc. and the Genesee Brewing
                    Company, Inc. dated April 30, 1997 to Monroe Brewing Co.,
                    LLC (now known as High Falls Brewing Company, LLC) dated
                    December 15, 2000.

          **+10.38  Guaranty of The Genesee Brewing Company, Inc. dated December
                    15, 2000 in favor of Boston Brewing Company, Inc., for
                    itself and as the sole general partner of Boston Beer
                    Company Limited Partnership in connection with the Consent
                    of Assignment of the Amended and Restated Agreement between
                    Boston Brewing Company, Inc. and the Genesee Brewing
                    Company, Inc. dated April 30, 1997 to Monroe Brewing Co.,
                    LLC (now known as High Falls Brewing Company, LLC) dated
                    December 15, 2000.

                                       5

<PAGE>
 
          **11.1    The information required by exhibit 11 has been included in
                    Note L of the notes to the consolidated financial
                    statements.

          21.1      List of subsidiaries of The Boston Beer Company, Inc.
                    (incorporated by reference to the Company's Form 10-K, filed
                    on March 28, 1997).

          *21.2     List of subsidiaries of The Boston Beer Company, Inc.
                    effective as of December 30, 2000

          *23.1     Consent of Arthur Andersen LLP, independent accountants with
                    respect to the Company.

          *27.1     Financial Data Schedule (electronic filing only).



* Filed with the Company's Annual Report on Form 10-K for the year ended
December 30, 2000.

** Filed with this Amendment to the Annual Report on Form 10-K.

+ Portions of this Exhibit have been omitted pursuant to an application for an
order declaring confidential treatment filed with the Securities and Exchange
Commission.

                                       6

<PAGE>
 

                                   SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities and
Exchange Act of 1934, the Registrant has duly caused this Amendment to its
Annual Report on Form 10-K to be signed on its behalf by the undersigned,
thereunto duly authorized, on this 16th day of October 2001.



                                           THE BOSTON BEER COMPANY, INC.


                                           /s/ Martin F. Roper
                                           President and Chief Executive Officer
                                           (principal executive officer)

                                       7




<PAGE>
 
Portions of this exhibit have been omitted and separately filed with the
Commission pursuant to a request for confidential treatment under Rule 24b-2.
The location of those omissions is denoted by opening and closing brackets as
follows: [ ].

                                                                   Exhibit 10.37
                                     CONSENT
                                     -------

     This CONSENT (this "Consent") is given by BOSTON BREWING COMPANY, INC.
d/b/a The Boston Beer Company, a Massachusetts corporation, for itself and as
the sole general partner of Boston Beer Company Limited Partnership, a
Massachusetts limited partnership, on behalf of said limited partnership
(collectively, "Boston Brewing"), to and in favor of THE GENESEE BREWING
COMPANY, INC., a New York corporation ("Genesee"), and MONROE BREWING CO., LLC,
a New York limited liability company ("Monroe Brewing").

                                R E C I T A L S :

     WHEREAS, Boston Brewing and Genesee are parties to an Amended and Restated
Agreement dated as of April 30, 1997 (the "Production Agreement"), pursuant to
which Boston Brewing produces certain of its proprietary beer products at the
Genesee brewery in Rochester, New York (the "Rochester Brewery");

     WHEREAS, Genesee has entered into an Asset Purchase Agreement dated as of
August 29, 2000, as amended by Amendment No. 1 dated as of December 15, 2000
(collectively, the "Purchase
 Agreement") with Monroe Brewing, pursuant to which
Genesee will sell to Monroe Brewing the Rochester Brewery and certain other
assets, subject to the terms and conditions stated therein, including a
condition that this Consent first be obtained from Boston Brewing;

     WHEREAS, Genesee wishes to assign the Production Agreement to Monroe
Brewing as part of the asset sale, and has requested the consent of Boston
Brewing to such assignment in accordance with the terms of the Assignment and
Assumption Agreement in the form attached hereto as Exhibit A (the
"Assignment"); and

     WHEREAS, Boston Brewing has agreed to the consent to the Assignment on the
terms and conditions set forth herein;

                              P R O V I S I O N S :

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, and intending to be legally bound,
Boston Brewing hereby agrees in favor of Genesee and Monroe Brewing as follows:

     1. Effective as of the closing of the transactions contemplated by the
Purchase Agreement, Boston Brewing hereby consents to, and approves the
Assignment, pursuant to Section 19 of the Production Agreement, on the following
conditions:

<PAGE>
 
     (a) This Consent is with a full reservation of all rights accruing to the
parties under the Production Agreement, and shall not be deemed to release any
party from any of their obligations under the Production Agreement, or to any
way affect the rights of the parties thereunder, except that Genesee's liability
thereunder shall be only as provided in the Guaranty referred to below; and

     (b) This Consent is given in reliance on the representation of Genesee and
Monroe Brewing that Schedule 1 attached hereto accurately reflects the current
ownership of Genesee and that Schedule 2 attached hereto accurately reflects the
ownership of Monroe Brewing as of the date hereof and immediately after the
effective date of the closing of the transactions contemplated by the Purchase
Agreement. Boston Brewing represents to Genesee and Monroe Brewing that Schedule
3 attached hereto accurately reflects the current ownership of Boston Brewing;
and

     (c) Genesee shall execute and deliver to Boston Brewing the Guaranty
attached hereto as Exhibit B (the "Guaranty").

     2. For so long as Genesee has continuing contingent liability to Boston
Brewing under the Guaranty, Boston Brewing and Monroe Brewing shall not, without
the prior written consent of Genesee, amend or modify the Production Agreement,
or fund, advance or otherwise provide monies or credit to Monroe Brewing, in any
manner that would increase or enlarge Genesee's duties, obligations or
liabilities under the Guaranty in any respect whatsoever as they exist on the
date hereof.

     3. Boston Brewing represents, warrants and acknowledges to Genesee and
Monroe Brewing as follows:

     (a) Boston Brewing has the corporate and partnership power and authority
and legal right to execute and deliver this Consent, perform its obligations
hereunder and consummate the transactions herein contemplated. The execution and
delivery by Boston Brewing of this Consent, the performance of its obligations
and consummation of the transactions contemplated hereunder have been duly
authorized by proper corporate and partnership proceedings, and this Consent
constitutes the legal, valid and binding obligation of Boston Brewing,
enforceable against Boston Brewing in accordance with its terms, except as
enforceability may be limited by bankruptcy, insolvency, reorganization or other
similar laws of general applicability and by the effect of general principles of
equity (regardless of whether enforceability is considered in a proceeding in
equity or at law).

     (b) The execution, delivery and performance by Boston Brewing of this
Consent are within its corporate powers, have been duly authorized by all
necessary corporate action, do not contravene or violate (i) Boston Brewing
Company, Inc.'s Certificate of Incorporation or By-Laws or Boston Beer Company
Limited Partnership's Limited Partnership Agreement or other governing
documents, (ii) any law, rule or regulation applicable to it, the contravention
or violation of which would or could reasonably be expected to have a material
adverse effect on Boston Brewing's

12/14/00

<PAGE>
 
financial condition, (iii) any restrictions under any material agreement,
contract or instrument to which it is a party, or by which it or any of its
property is bound, the contravention or violation of which would or could
reasonable be expected to have a material adverse effect on Boston Brewing's
financial condition or (iv) any material order, writ, judgment, award,
injunction or decree binding on or affecting it or its property, the
contravention or violation of which would or could reasonably be expected to
have a material adverse effect on Boston Brewing's financial condition, and do
not result in the creation or imposition of any adverse claim on the assets of
Boston Brewing.

     (c) Boston Brewing has not transferred, assigned or granted any interest of
any kind at any time in the Production Agreement (or any earlier version
thereof) to any other party whatsoever, and its right, title and interest
therein are free from any security interest, lien or encumbrance of any kind.

     (d) to the best of its knowledge, Genesee is in full compliance with the
Production Agreement and is not in breach or default of any of the terms
thereof. No press releases or other public statements with respect to the
relationship between Boston Brewing and Genesee and Monroe Brewing shall be made
by any of the parties to this Agreement without the prior written consent of the
other parties, provided, however, that any party may make any public disclosure
which it believes in good faith to be required by law.
     
     EXECUTED this 15th day of December, 2000.

                                  BOSTON BREWING COMPANY, INC. d/b/a
                                  THE BOSTON BEER COMPANY, for itself and
                                  as the sole general partner of BOSTON BEER
                                  COMPANY LIMITED PARTNERSHIP


                                  By:
                                        ----------------------------------------
                                        RICHARD P. LINDSAY
                                  Name: Richard P. Lindsay
                                  Title: Vice President

                                LIST OF EXHIBITS
                                ----------------

                Exhibit A   -   Assignment and Assumption Agreement
                Exhibit B   -   Guaranty

Monroe Brewing Co., LLC hereby signs this Consent for the sole purpose of
agreeing in favor of Boston Brewing Company, Inc. d/b/a The Boston Beer Company,
for itself and as the sole general partner of Boston Beer Company Limited
Partnership that any breach by Genesee of its obligations

12/14/00

<PAGE>
 
under the Guaranty referred to above, including, without limitation, Genesee's
failure to maintain the Required Net Worth specified in Section 2(b) of the
Guaranty, shall constitute a default by Monroe Brewing under the Production
Agreement.
                                  MONROE BREWING CO., LLC


                                  By:
                                        ----------------------------------------
                                        SAMUEL T. HUBBARD, JR.
                                  Name:
                                  Title: Manager

<PAGE>
 
                              EXHIBIT A TO CONSENT

                       ASSIGNMENT AND ASSUMPTION AGREEMENT
                       -----------------------------------

     This ASSIGNMENT AND ASSUMPTION AGREEMENT (this "Agreement") is made as of
the ___ day of _______, 2000 by and between by MONROE BREWING CO., LLC, a New
York limited liability company ("Monroe Brewing"), and THE GENESEE BREWING
COMPANY, INC., a New York corporation ("Genesee").

                                R E C I T A L S :

     WHEREAS, Genesee and Monroe Brewing have entered into an Asset Purchase
Agreement dated August 29, 2000, as amended by Amendment No. 1 dated as of
December 15, 2000 (collectively, the "Purchase Agreement"), pursuant to which
Genesee has agreed to sell and transfer and assign to Monroe Brewing, and Monroe
Brewing has agreed to purchase from Genesee, substantially all of Genesee's
assets necessary to operate Genesee's brewing business;

     WHEREAS, one of the assets to be transferred under the Purchase Agreement
includes all of Genesee's right, title and interest in and to an Amended and
Restated Agreement dated as of April 30, 1997 (the "Production Agreement')
between Genesee and Boston Brewing Company, Inc., d/b/a The Boston Beer Company,
a Massachusetts corporation, for itself and as the sole general partner of
Boston Beer Company Limited Partnership, a Massachusetts limited partnership
(collectively, "Boston Brewing"), pursuant to which Genesee agreed to supply
Boston Brewing, and Boston Brewing agreed to purchase from Genesee, on an
as-ordered basis, Samuel Adams Boston Lager and certain other Boston Brewing
products;

     WHEREAS, it is a condition to Genesee's and Monroe Brewing's obligations
under the Purchase Agreement that Boston Brewing consent to such transfer on
terms and conditions reasonably acceptable to Genesee and Monroe Brewing, and
Boston Brewing has done so pursuant to a Consent dated as of December ___, 2000
(the "Consent"), which conditions the effectiveness of such Consent on Genesee's
execution and delivery of a Guaranty in the form annexed to the Consent (the
"Guaranty");

     WHEREAS, Genesee has agreed to provide the Guaranty to Boston Brewing,
provided that Monroe Brewing and Genesee enter into an Indemnification Agreement
in the form of Exhibit A annexed hereto (the "Indemnification Agreement"); and
               ---------

     WHEREAS, all capitalized terms not otherwise defined herein shall have the
meanings given thereto in the Purchase Agreement;

<PAGE>
 
                              P R O V I S I O N S :

     NOW, THEREFORE, in consideration of the foregoing and the mutual covenants
and promises set forth in the Purchase Agreement and herein, and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties agree as follows:

     1. Assignment and Assumption. Genesee hereby sells, assigns, transfers and
sets over unto Monroe Brewing, free and clear of all liens and encumbrances, all
of its rights, benefits, privileges, title, and interest under, in and to the
Production Agreement. Genesee also hereby sells, assigns, transfers and sets
over unto Monroe Brewing all obligations, duties, covenants and responsibilities
of Genesee under, in and to the Production Agreement that arise after the
Closing, based on facts occurring subsequent thereto or which are contingent
upon the occurrence of the Closing, including, but not limited to, the
"Refunding Obligations," being any obligation relating to any change parts,
modifications or new equipment paid, funded or provided by Boston Brewing
pursuant to the Production Agreement, whether before or after the Closing,
including, without limitation, Genesee's No. 2 line. Monroe Brewing hereby
accepts such assignment and assumes and agrees to pay, perform and discharge all
obligations, duties, covenants and responsibilities of Genesee under said
Production Agreement that arise as a result of the Closing, or which arise after
the Closing, based on facts occurring subsequent thereto or which are contingent
upon the occurrence of the Closing (including, but not limited to, the Refunding
Obligations, if any), and agrees to abide and be bound by all terms of same, all
as though the Production Agreement had been made, executed and delivered by
Monroe Brewing. Nothing in this Agreement shall be construed to be a
modification of, or limitation on, any provision of the Production Agreement,
including any representations or warranties contained therein.

     2. Indemnification Agreement. Simultaneously with the execution and
delivery hereof, Genesee shall execute and deliver to Boston Brewing the
Guaranty, which shall be dated the date hereof, and Genesee and Monroe Brewing
shall enter into the Indemnification Agreement, which shall also be dated the
date hereof.

     3. Representation and Warranty. Genesee represents and warrants that a true
and complete copy of the Production Agreement is annexed hereto as Exhibit B.

     4. Benefits. The execution and delivery of this Agreement shall not be
deemed to confer any rights upon any person or entity other than the parties
hereto and, where allowed by this Agreement or the Exhibits hereto, their
respective successors and assigns, or make any person or entity a third party
beneficiary of this Agreement, or obligate the parties to any person or entity
other than the parties to this Agreement.

     5. Execution of Documents. Monroe Brewing shall take such actions and
execute such documents as Genesee may reasonably request from time to time in
order to consummate the transactions contemplated hereby.

12/14/00

<PAGE>
 
     6. Successors and Assigns. This Agreement shall be binding upon and inure
to the benefit of the parties and their respective successors and permitted
assigns.

     7. Entire Agreement. This Agreement, the Indemnification Agreement, the
Purchase Agreement and all instruments or agreements executed and delivered
thereunder constitute the entire agreement between the parties with respect to
the subject matter hereof, supersedes all prior and contemporaneous agreements
or understandings of the parties with respect thereto, and may not be modified,
amended or otherwise changed in any manner, except by a writing executed by a
duly authorized representative of the party to be charged.

     8. Governing Law. This Agreement is made and executed under and in all
respects is to be governed and construed under the laws of the State of New York
without consideration of conflicts of law principles. IN WITNESS WHEREOF, the
parties hereto have executed this Agreement as of the day and year first set
forth above.

                                  THE GENESEE BREWING COMPANY, INC.

                                  By:
                                      ------------------------------------------
                                  Name:
                                  Title:

                                  MONROE BREWING CO., LLC:

                                  By:
                                      ------------------------------------------
                                  Name:
                                  Title:

                                LIST OF EXHIBITS
                                ----------------

                     Exhibit A          -           Indemnification Agreement
                     Exhibit B          -           Production Agreement

<PAGE>
 
                              EXHIBIT B TO CONSENT

                                    GUARANTY
                                    --------

     This GUARANTY (this "Guaranty") is made this ____ day of ______ , 2000, by
THE GENESEE BREWING COMPANY, INC., a New York corporation ("Genesee"), in favor
of BOSTON BREWING COMPANY, INC., d/b/a The Boston Beer Company, a Massachusetts
corporation, for itself and as the sole general partner of Boston Beer Company
Limited Partnership, a Massachusetts limited partnership (collectively, "Boston
Brewing"). 

                               R E C I T A L S :

     WHEREAS, Genesee and Boston Brewing are parties to an Amended and Restated
Agreement dated as of April 30, 1997 (the "Production Agreement"), under which
Genesee has agreed to supply Boston Brewing, and Boston Brewing has agreed to
purchase from Genesee, on an as-ordered basis, Samuel Adams Boston Lager and
certain other Boston Brewing products;

     WHEREAS, Genesee and Monroe Brewing Co., LLC ("Monroe Brewing") have
entered into an Asset Purchase Agreement dated of August 29, 2000, as amended by
Amendment No. 1 dated as of December 15, 2000 (collectively, the "Purchase
Agreement"), pursuant to which Genesee has agreed to sell to Monroe, and Monroe
has agreed to purchase from Genesee, substantially all of the assets necessary
to operate Genesee's brewing business, including, but not limited to, all of
Genesee's right, title and interest in and to the Production Agreement; and

     WHEREAS, at Genesee's request, Boston Brewing has consented to the transfer
of the Production Agreement from Genesee to Monroe Brewing pursuant to a certain
Consent dated December ___, 2000 (the "Consent"), which conditions the
effectiveness of consent on Genesee's execution and delivery to Boston Brewing
of a guaranty in favor of Boston Brewing substantially in the form hereof;

                              P R O V I S I O N S :

     NOW, THEREFORE, in consideration of the Consent provided by Boston Brewing
and other good and valuable consideration, Genesee hereby agrees in favor of
Boston Brewing as follows:

     1. Performance Guaranty.

        (a) Subject to the terms and conditions herein, Genesee hereby 
guarantees the due, punctual and faithful performance by Monroe Brewing of its
obligations, duties, covenants and responsibilities under the Production
Agreement that arise after the closing under the Purchase Agreement based on
facts occurring subsequent thereto. Genesee hereby specifically further agrees
that in the event Monroe Brewing, for any reason, is obligated to perform under
the Production

<PAGE>
 
Agreement and it fails to do so in accordance with the terms thereof, Genesee
will, upon written notice from Boston Brewing, become liable to Boston Brewing
for any sum or sums Monroe Brewing has to pay Boston Brewing under the terms of
the Production Agreement for failure to perform or pay, subject to the terms and
conditions contained therein or any defenses thereto which either Monroe Brewing
may have or which Genesee may have.

        (b) Notwithstanding anything herein to the contrary, Genesee's
obligations under this Guaranty and the Production Agreement shall terminate and
be of no further force or effect upon the expiration of 1,095 days after the
"Closing Date" (as defined in the Purchase Agreement) (the "Termination Date"),
provided that any claims made in writing by Boston Brewing against Genesee
hereunder prior to the Termination Date and remaining unresolved or outstanding
as of such date shall survive until the earlier to occur of the payment or the
final resolution and satisfaction of such claims to the extent and subject to
the terms and conditions herein. The period between the Closing Date and the
Termination Date is referred to herein as the "Guaranty Period."

     2. Net Worth Maintenance. 

        (a) During the Guaranty Period, Genesee will maintain a Liquid Net Worth
(defined for this purpose as the excess of (i) unencumbered (1) cash and
currency on hand and on deposit, demand deposits and checks held, (2)
short-term, highly liquid investments that are readily convertible to known
amounts of cash plus (3) marketable securities over (ii) total liabilities, each
as determined in accordance with generally accepted accounting practices), in an
amount that, in the aggregate, is not less than the following:

               First 365 days after Closing Date:           [$           ]
               Second 365 days after Closing Date:          [$           ]
               Third 365 days after Closing Date:           [$           ]

        (b) After the Guaranty Period, Genesee will maintain a Liquid Net Worth 
in an amount that, in the aggregate, is not less than the amount of any claims
made by Boston Brewing in accordance with Section 1 hereof that remain
unresolved.

     3. Enforcement / Notice.

        (a) If Monroe Brewing fails to perform any of its duties under the
Production Agreement guaranteed hereby, then Boston Brewing may proceed directly
to make a claim against Genesee to be paid by Genesee without necessity of any
suit or proceeding by Boston Brewing against Monroe Brewing. Genesee shall be
entitled to assert any defenses or claims that Genesee or Monroe Brewing may
have under the Production Agreement or otherwise against any claim made by
Boston Brewing and does not otherwise waive any defenses whatsoever to its
obligations hereunder or under the Production Agreement. Anytime, with or
without consideration or notice, Boston Brewing may waive enforcement of the
terms, conditions and provisions of this Guaranty with respect to any breach or
default by Monroe Brewing, and such waiver will not diminish or

<PAGE>
 
otherwise affect Monroe Brewing's obligations to Boston Brewing under the
Production Agreement. Genesee agrees that in the event any of the foregoing
provisions are found to be unenforceable, that portion so found will in no way
affect the purpose and intent of the remaining provisions, and to that extent
those provisions will remain binding upon the parties.

        (b) Any claim, notice or other communication under this Guaranty shall
be in writing, and shall be deemed duly given when delivered personally or by
facsimile, or four days after being mailed by registered mail, return receipt
requested, or by documented over-night delivery to a party at the following
address (or such other address as such party may have specified by notice given
to the other party pursuant to this provision):

                    If to Genesee, to:

                             Mark W. Leunig, Vice President
                             The Genesee Corporation
                             P.O. Box 762
                             Rochester, New York 14603

                    with a copy to:

                             Monroe Brewing Co., LLC
                             445 St. Paul Street
                             Rochester, New York 14605
                             Attention: Samuel T. Hubbard, Jr., President

                    If to Boston Brewing, to:

                             c/o The Boston Beer Company
                             75 Arlington Street
                             Boston, MA 02116
                             Attention: Martin F. Roper, President

     4. Subrogation. Genesee shall be entitled to, and shall be fully subrogated
to all of Boston Brewing's rights under the Production Agreement with respect
to, and to the extent of, payments made by Genesee pursuant to this Guaranty,
and Boston Brewing hereby assigns any rights that may arise in connection with
such payment to enforce any remedy which Boston Brewing may have against Monroe
Brewing therefor.

     5. Amendments and Modification to Production Agreement. As a condition to
Genesee's continuing liability hereunder, by its acceptance hereof, Boston
Brewing hereby acknowledges that Monroe Brewing has agreed with Genesee that, so
long as Genesee has any liability to Boston Brewing, it shall not agree to amend
or modify the Production Agreement, or to accept any funding, advances or other
monies or credit from Boston Brewing, in any manner that

<PAGE>
 
would in any way increase or enlarge Genesee's duties, obligations or
liabilities Boston Brewing without Genesee's prior written consent. Accordingly,
no such amendment or modification shall be effective unless it is accompanied or
preceded by Genesee's written consent.

     6. Representations and Warranties.

        (a) Genesee has the corporate power and authority and legal right to
execute and deliver this Guaranty, perform its obligations hereunder and
consummate the transactions herein contemplated. The execution and delivery by
Genesee of this Guaranty and the performance of its obligations and consummation
of the transactions contemplated hereunder have been duly authorized by proper
corporate proceedings, and this Guaranty constitutes the legal, valid and
binding obligation of Genesee, enforceable against Genesee in accordance with
its terms, except as enforceability may be limited by bankruptcy, insolvency,
reorganization or other similar laws of general applicability, and by the effect
of general principles of equity (regardless of whether enforceability is
considered in a proceeding in equity or at law).

        (b) The execution, delivery and performance by Genesee of this Guaranty
are within its corporate powers, have been duly authorized by all necessary
corporate action, do not contravene or violate (i) its Certificate of
Incorporation or By-laws, (ii) any law, rule or regulation applicable to it, the
contravention or violation of which would or could reasonably be expected to
have a material adverse effect on Genesee's financial condition, (iii) any
restrictions under any material agreement, contract or instrument to which it is
a party or by which it or any of its property is bound, the contravention or
violation of which would or could reasonably be expected to have a material
adverse effect on Genesee's financial condition or (iv) any material order,
writ, judgment, award, injunction or decree binding on or affecting it or its
property, the contravention or violation of which would or could reasonably be
expected to have a material adverse effect on Genesee's financial condition, and
do not result in the creation or imposition of any adverse claim on the assets
of Genesee.

     7. Assignment.

        (a) Notwithstanding anything herein to the contrary, Genesee may assign
this Guaranty to its parent corporation or any affiliate thereof, provided that
the assignee assumes all of Genesee's obligations hereunder, including, but not
limited to, those set forth in Section 2 hereof, and provided that a copy of
such assignment and assumption is delivered to Boston Brewing. Upon such
delivery, Genesee shall be relieved of any obligations hereunder.

        (b) This Guaranty shall be for the sole benefit of Boston Brewing and 
its parent corporation or any affiliate thereof and may not be assigned by
Boston Brewing other than as part of a corporate reorganization that does not
effect a change in control, within the meaning of Section 10(e) of the
Production Agreement, or enforced by anyone but Boston Brewing and its parent
corporation or any affiliate thereof, provided that no such assignment of this
Guaranty to the parent corporation or any affiliate of Boston Brewing shall be
valid unless such parent corporation or affiliate is also the assignee of the
Production Agreement.

<PAGE>
 
     8. Entire Agreement; Amendments or Modification. This Guaranty together
with the Production Agreement (as modified hereby) and the Consent constitute
the entire agreement between the parties regarding the subject matter hereof,
and Genesee shall have no other liabilities or obligations of any kind to Boston
Brewing with respect to the Production Agreement or otherwise, except as
expressly provided herein. This Guaranty may not be amended or modified except
with a writing executed by both parties.

     9. Governing Law. This Guaranty, as well as all rights and obligations of
the parties hereto, shall be given, construed and interpreted according to the
internal laws of the State of New York.

     IN WITNESS WHEREOF, Genesee has executed this Guaranty as of the date first
written above.

                                       THE GENESEE BREWING COMPANY, INC.

                                       By:
                                          --------------------------------------
                                       Name:
                                       Title:

Accepted and Agreed:
Boston Brewing Company, Inc. d/b/a
The Boston Beer Company, for itself and
as the sole general partner of Boston Beer
Company Limited Partnership

By:
   --------------------------------------
Name:
Title:

<PAGE>
 
                              Schedule 1 to Consent
                              ---------------------

The Genesee Brewing Company, Inc. is authorized to issue 100 shares of Common
Stock, $1.00 par value, all of which is owned by Genesee Corporation. 

Genesee Corporation is a public company. 61% of the Class A voting stock of
Genesee Corporation is owned or controlled by Charles S. Wehle, as more fully
described Item 12(b) of the Form 10-K filed by Genesee Corporation for its
fiscal year ended April 29, 2000.

<PAGE>
 
 Monroe Brewing Co, LLC                                    Schedule 2 to Consent
 Subscription Agreements
 Status as of 12/5/00

 Investment Commitment
[------------------------------------------------------------------------------]

<PAGE>
 
                              Schedule 3 to Consent
                              ---------------------

Boston Brewing Company, Inc. has 1,000 issued and outstanding shares of no par
value common stock, all of which are owned by the Boston Beer Company, Inc.

Class A Common Stock, $.01 par value, of The Boston Beer Company, Inc. is
publicly traded, of which C. James Koch beneficially owns approximately 29%. Mr.
Koch also owns 100% of the Company's Class B Common Stock, $.01 par value. A
more detailed description of the ownership of the Company is set forth in Item
12(b) of the Form 10-K filed by the Boston Beer Company, Inc. for its fiscal
year ended December 25, 1999.


<PAGE>
 
Portions of this exhibit have been omitted and separately filed with the
Commission pursuant to a request for confidential treatment under Rule 24b-2.
The location of those omissions is denoted by opening and closing brackets as
follows: [ ].

                                                                   Exhibit 10.38
                                    GUARANTY

     This GUARANTY (the "Guaranty") is made this 15 day of December, 2000, by
THE GENESEE BREWING COMPANY, INC., a New York corporation ("Genesee"), in favor
of BOSTON BREWING COMPANY, INC., d/b/a The Boston Beer Company, a Massachusetts
corporation, for itself and as the sole general partner of Boston Beer Company
Limited Partnership, a Massachusetts limited partnership (collectively, "Boston
Brewing").

                                R E C I T A L S:

     WHEREAS, Genesee and Boston Brewing are parties to an Amended and Restated
Agreement dated as of April 30, 1997 (the "Production Agreement"), under which
Genesee has agreed to supply Boston Brewing, and Boston Brewing has agreed to
purchase from Genesee, on an as-ordered basis, Samuel Adams Boston Lager and
certain other Boston Brewing products;

     WHEREAS, Genesee and Monroe Brewing Co., LLC ("Monroe Brewing") have
entered into an Asset Purchase Agreement dated of August 29, 2000, as amended by
Amendment No. 1 dated as of December 15, 2000 (collectively, the "Purchase

Agreement"), pursuant to which Genesee has agreed to sell to Monroe, and Monroe
has agreed to purchase from Genesee, substantially all of the assets necessary
to operate Genesee's brewing business, including, but not limited to, all of
Genesee's right, title and interest in and to the Production Agreement; and

     WHEREAS, at Genesee's request, Boston Brewing has consented to the transfer
of the Production Agreement from Genesee to Monroe Brewing pursuant to a certain
Consent dated December 15, 2000 (the "Consent"), which conditions the
effectiveness of consent on Genesee's execution and delivery to Boston Brewing
of a guaranty in favor of Boston Brewing substantially in the form hereof;

                              P R O V I S I O N S:

     NOW, THEREFORE, in consideration of the Consent provided by Boston Brewing
and other good and valuable consideration, Genesee hereby agrees in favor of
Boston Brewing as follows:

     1. Performance Guaranty.

        (a) Subject to the terms and conditions herein, Genesee hereby
guarantees the due, punctual and faithful performance by Monroe Brewing of its
obligations, duties, covenants and responsibilities under the Production
Agreement that arise after the closing under the Purchase Agreement based on
facts occurring subsequent thereto. Genesee hereby specifically further agrees
that in the event Monroe Brewing, for any reason, is obligated to perform under
the Production Agreement and it fails to do so in accordance with the terms
thereof, Genesee will, upon written notice from Boston Brewing, become liable to
Boston Brewing for any sum or sums Monroe Brewing has to pay Boston Brewing
under the terms of the Production Agreement

<PAGE>
 
for failure to perform or pay, subject to the terms and conditions contained
therein or any defenses thereto which either Monroe Brewing may have or which
Genesee may have.

        (b) Notwithstanding anything herein to the contrary, Genesee's 
obligations under this Guaranty and the Production Agreement shall terminate and
be of no further force or effect upon the expiration of 1,095 days after the
"Closing Date" (as defined in the Purchase Agreement ) (the "Termnation Date"),
provided that any claims made in writing by Boston Brewing against Genesee
hereunder prior to the Termination Date and remaining unresolved or outstanding
as of such date shall survive until the earlier to occur of the payment or the
final resolution and satisfaction of such claims to the extent and subject to
the terms and conditions herein. The period between the Closing Date and the
Termination Date is referred to herein as the "Guaranty Period."

     2. Net Worth Maintenance.

        (a) During the Guaranty Period, Genesee will maintain a Liquid Net Worth
(defined for this purpose as the excess of (i) unencumbered (1) cash and net
currency on hand and on deposit, demand deposits and checks held, (2)
short-term, highly liquid investments that are readily convertible to known
amounts of cash plus (3) marketable securities over (ii) total liabilities, each
as determined in accordance with generally acceptable accounting practices), in
an amount that, in the aggregate, is not less than the following:

           First 365 days after Closing Date:         [$          ]
           Second 365 days after Closing Date         [$          ]
           Third 365 days after Closing Date          [$          ]

        (b) After the Guaranty Period, Genesee will maintain a Liquid Net Worth
in an amount that, in the aggregate, is not less than the amount of any claims
made by Boston Brewing in accordance with Section 1 hereof that remain
unresolved.

3. Enforcement / Notice.

        (a) If Monroe Brewing fails to perform any of its duties under the
Production Agreement guaranteed hereby, then Boston Brewing may proceed directly
to make a claim against Genesee to be paid by Genesee without necessity of any
suit or proceeding by Boston Brewing against Monroe Brewing. Genesee shall be
entitled to assert any defenses or claims that Genesee or Monroe Brewing may
have under the Production Agreement or otherwise against any claim made by
Boston Brewing and does not otherwise waive any defenses whatsoever to its
obligations hereunder or under the Production Agreement. Anytime, with or
without consideration or notice, Boston Brewing may waive enforcement of the
terms, conditions and provisions of this Guaranty with respect to any breach or
default by Monroe Brewing, and such waiver will not diminish or otherwise affect
Monroe Brewing's obligations to Boston Brewing under the Production Agreement.
Genesee agrees that in the event any of the foregoing provisions are found to be
unenforceable, that portion so found will in no way affect the purpose and
intent of the remaining provisions, and to the extent those provisions will
remain binding upon the parties.

<PAGE>
 
        (b) Any claim, notice or other communication under this Guaranty shall 
be in writing, and shall be deemed duly given when delivered personally or by
facsimile, or four days after being mailed by registered mail, return receipt
requested, or by documented over-night delivery to a party at the following
address (or such other address as such party may have specified by notice given
to the other party pursuant to this provision):

              If to Genesee, to:

                    Mark W. Leunig, Vice President
                    The Genesee Corporation
                    P.O. Box 762
                    Rochester, New York 14603

              with a copy to:

                    Monroe Brewing Co., LLC
                    445 St. Paul Street
                    Rochester, New York 14605
                    Attention: Samuel T. Hubbard, Jr., President

              If to Boston Brewing, to:

                    c/o The Boston Beer Company
                    75 Arlington Street
                    Boston, MA 02116
                    Attention: Martin F. Roper, President

     4. Subrogation. Genesee shall be entitled to, and shall be fully subrogated
to all of Boston Brewing's rights under the Production Agreement with respect
to, and to the extent of, payments made by Genesee pursuant to this Guaranty,
and Boston Brewing hereby assigns any rights that may arise in connection with
such payment to enforce any remedy which Boston Brewing may have against Monroe
Brewing therefor.

     5. Amendments and Modification to Production Agreement. As a condition to
Genesee's continuing liability hereunder, by its acceptance hereof, Boston
Brewing hereby acknowledges that Monroe Brewing has agreed with Genesee that, so
long as Genesee has any liability to Boston Brewing, it shall not agree to amend
or modify the Production Agreement, or to accept any funding, advances or other
monies or credit from Boston Brewing, in any manner that would in any way
increase or enlarge Genesee's duties, obligations or liabilities Boston Brewing
without Genesee's prior written consent. Accordingly, no such amendment or
modification shall be effective unless it is accompanied or preceded by
Genesee's written consent.

<PAGE>
 
     6. Representatives and Warranties.

        (a) Genesee has the corporate power and authority and legal right to
execute and deliver this Guaranty, perform its obligations hereunder and
consumate the transactions herein contemplated. The execution and delivery by
Genesee of this Guaranty and the performance of its obligations and consummation
of the transactions contemplated hereunder have been duly authorized by proper
corporate proceedings, and this Guaranty constitutes the legal, valid and
binding obligation of Genesee, enforceable against Genesee in accordance with
its terms, except as enforceability may be limited by bankruptcy, and by the
effect of general principles of equity (regardless of whether enforceability is
considered in a proceeding in equity or at law).

        (b) The execution, delivery and performance by Genesee of this Guaranty 
are within its corporate powers, have been duly authorized by all necessary
corporate action, do not contravene or violate (i) its Certificate of
Incorporation or By-laws, (ii) any law, rule or regulation applicable to it, the
contravention or violation of which would or could be expected to have a
material adverse effect on Genesee's financial condition, (iii) any restrictions
under any material agreement, contract or instrument to which it is a party or
by which it or any of its property is bound, the contravention or violation of
which would or could reasonably be expected to have a material adverse effect on
Genesee's financial condition or (iv) any material order, writ, judgment, award,
injunction or decree binding on or affecting it or its property, the
contravention or violation of which would or could reasonably be expected to
have a material adverse effect or imposition of any adverse claim on the assets
of Genesee.

     7. Assignment. 

        (a) Notwithstanding anything herein to the contrary, Genesee may assign
this Guaranty to its parent corporation or any affiliate thereof, provided that
the assignee assumes all of Genesee's obligations hereunder, including, but not
limited to, those set forth in Section 2 hereof, and provided that a copy of
such assignment and assumption is delivered to Boston Brewing. Upon such
delivery, Genesee shall be relieved of any obligations hereunder.

        (b) This Guaranty shall be for the sole benefit of Boston Brewing and 
its parent corporation or any affiliate thereof and may not be assigned by
Boston Brewing other than as part of a corporate reorganization that does not
effect a change in control, within the meaning of Section 10(e) of the
Production Agreement, or enforced by anyone but Boston Brewing and its parent
corporation or any affiliate thereof, provided that no such assignment of this
Guaranty to the parent corporation or any affiliate of Boston Brewing shall be
valid unless such parent corporation or affiliate is also the assignee of the
Production Agreement.

     8. Entire Agreement; Amendments or Modification. This Guaranty together
with the Production Agreement (as modified hereby) and the Consent constitute
the entire agreement between the parties regarding the subject matter hereof,
and Genesee shall have no other liabilities or obligations of any kind to Boston
Brewing with respect to the Production Agreement or otherwise, except as
expressly provided herein. This Guaranty may not be amended or modified except
with a writing executed by both parties.

<PAGE>
 
     9. Governing Law. This Guaranty, as well as all rights and obligations of
the parties hereto, shall be given, construed and interpreted according to the
internal laws of the State of New York.

     IN WITNESS WHEREOF, Genesee has executed this Guaranty as of the date first
written above.

                                  THE GENESEE BREWING COMPANY, INC

                                  By:    MARK W. LEUNIG
                                         ---------------------------------------
                                  Name:  Mark W. Leunig
                                  Title: Vice President
Accepted and Agreed:
Boston Brewing Company, Inc. d/b/a
The Boston Beer Company, for itself
and as the sole general partner of Boston Beer
Company Limited Partnership

By:    RICHARD P. LINDSAY
       ---------------------------------------
Name:  Richard P. Lindsay
Title: Vice President