in the regenerator section, passes over stainless steel plates where it is heated by hot
water or steam on the opposite side of the plates to a temperature of at least 161F
(72C).
h. Holding Tube. From the final heater, the milk flows through the holding tube
(see block 8, figure 1-3) where it is "held" for at least 15 seconds. The "holding time"
shall be taken to mean flow time of the fastest particle of milk, at or above 161F (72C),
throughout the holding tube section. The maximum velocity of the milk through the
holding tube is governed by the speed of the timing pump, the diameter and length of
the holding tube, and surface friction. The Grade A Pasteurized Milk Ordinance
requires that the holding time be tested by the health authority when the equipment is
initially installed and semiannually thereafter, and, also, at any time an alteration or
repair may offset the holding time, or when the seal of the speed-setting device on the
timing pump has been broken.
i. Flow Diversion Valve. After the milk flows through the holding tube, it
passes the recorder-controller sensor. The recorder-controller sensor regulates the
forward or diverted flow position of the flow-diversion valve (see block 9, figure 1-3). If
milk passing the recorder-controller sensor is 161F (72C) or higher, the flow-diversion
valve assumes a forward-flow position and the milk flows forward into the pasteurized
section of the regenerator. If the milk is less than 161F (72C) when it passes the
recorder-controller sensor, the flow-diversion valve assumes a diverted-flow position
and the inadequately heated milk is diverted back into the raw milk balance tank.
j. Regenerator (Cooling Section). Properly heated milk flows through the
flow-diversion valve into the pasteurized side of the regenerator section of the HTST
(see block 10, figure 1-3). In the regenerator section, the pasteurized milk is cooled to
approximately 90F (32C) by incoming cold raw milk on the opposite side of the
stainless steel plates. The warm pasteurized milk then passes through the cooling
section of the HTST (see block 11, figure 1-3), where a coolant, on the opposite side of
stainless steel plates, reduces the temperature to 40F (4C) or below. The cold
pasteurized milk then passes to a storage tank to await packaging.
1-20. HHST PASTEURIZER
Some processing companies operate a type of pasteurizer that reduces the
pasteurization time even more than the HTST. Some units are similar to the HTST
plate pasteurizer, except that the hot water in the heating unit is replaced by steam
under pressure and the holding tube is shortened. In this type pasteurizer, the milk is
heated from 191F (88C) to 212F (100C) and held for no more than 1 second. (See
the temperature and time requirements shown in Table 1-1.)
MD0715
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