U. S. Food and Drug Administration
Center for Food Safety and Applied Nutrition
FDA Prime Connection

M-a-89 - Reclaim. Heat From Vapors, etc. (03/25/96)
 
 
HHS:PHS:FDA:CFSAN:OFP:DCP:MSB
                                  200 C Street, S.W.
                                Washington, DC 20204
 
                                              M-a-89
 
                                      March 25, 1996
 
 
 
TO:       All Regional Food and Drug Directors
          Attn:  Regional Milk Specialists
 
FROM:     Chief,  Milk Safety Branch (HFS-626)
 
SUBJECT:  Reclaiming Heat from Vapors Drawn from
          Pasteurized Milk and Milk Products for
          Heating Raw Milk (PMO, Item 16p(D)-
          Regenerative Heating or Item 15p(B)-Cross-
          connections)
 
This memorandum does not apply to or restrict
reclaiming of heat from thick walled heat
exchangers, such as chest-type heat exchangers or
evaporators, or to the reclaiming of heat from
properly protected "cow" water condensed from such
vapors, or to reclaiming heat from systems with two
or more heat exchangers which use a properly
protected heating medium to isolate raw milk from
vapor.
 
                     BACKGROUND
 
Steam-type vacuum chambers are sometimes located
after the holding tube of a continuous flow
pasteurizer.  In some milk processing plants we have
observed the vapor from these vacuum chambers being
used to heat raw milk in plate type heat exchangers
located in the piping between the vacuum chamber and
the vacuum pump(s).
 
These water sealed vacuum pump(s) generate a very
strong vacuum (18 to 22 inches of mercury depending
upon the altitude). The vapor being pulled through
the pasteurized side of the heat exchanger will
normally be under much less pressure (more vacuum)
than the raw milk being heated. If there is leakage
in a heat exchanger, raw milk will be drawn into the
pasteurized side of the heat exchanger.
 
When the vacuum pump(s) stop, or in some cases when
the water providing the water seal stops, the vacuum
in the piping will be immediately relieved and the
vacuum in the system will begin to immediately
equalize. The largest reservoir of vacuum in these
systems is the vacuum chamber. This means that there
can be an almost explosive movement of liquids and
aerosols, possibly containing raw milk, from the
piping and pasteurized side of the heat exchanger
toward and possibly into the vacuum chamber.
 
If such a plate heat exchanger is located within a
pasteurizer, it constitutes a raw to pasteurized
regenerator. If the pasteurized product is not
adequately protected from the raw milk, it is in
violation of item 16p(D). If such a plate heat
exchanger is located outside of a pasteurization
system and the pasteurized product is not adequately
isolated from the raw milk , it is in violation of
item 15p,B.
 
After an exhaustive review of systems using vapors
in a plate heat exchanger for regeneration purposes,
and dispite continuing industry efforts, FDA remains
unaware of any means to adequately protect
pasteurized milk in the vacuum chamber from raw milk
when a loss of vacuum occurs.
 
Therefore  item 16p(D) or 15p(B) could be debited
when this practice is observed during ratings or
check-ratings.
 
This interpretation does not preclude future
acceptance by FDA of any installation which will
provide the needed public health protection.
 
In accordance with Problem 326 adopted at the 1993
NCIMS Conference, judgement should be used with
regard to whether this item is debited at the first
state rating and FDA check-rating conducted in each
milk plant after this memorandum becomes
enforceable.
 
This interpretation was issued in accordance with
the guidelines for issuance of interpretations and
was distributed to all state milk regulatory and
rating officials for comment.  Comments received by
the NCIMS Executive Secretary were considered by the
NCIMS Executive Board and the FDA and were
incorporated into this document when it was agreed
to be appropriate.  This memorandum is effective on
March 25, 1996.
 
Copies of this memorandum are provided for
distribution to State Milk Regulatory Agencies,
State Milk Sanitation Rating Officers, and FDA
District and Regional Milk Specialists.  This
memorandum is also available on the FDA Prime
Connection computer bulletin board system and should
be made readily available to the dairy industry and
any other interested parties.
 
 
 
                              Joseph M. Smucker
                              Chief, Milk Safety
                              Branch
                              Center for Food Safety
                                   and  Applied
                                        Nutrition