(PMO, Item 16p(D))
200 C Street, S.W.
Washington, DC 20204
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.
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, judgment 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