Pasteurization, flash

Natural style juices that contain the cloud are increasing in popularity, especiaHy apple juices, because these retain more fresh flavor if processed carefuUy. Optimum processing conditions chill the fmit to 4°C before milling, add 500 ppm ascorbic acid to retard browning, press under nitrogen, and flash pasteurize the juice as quickly as possible (4). 

The occurrence of a peroxidase, lactoperoxidase (LPO), in milk was recognized as early as 1881. It is one of the most heat-stable enzymes in milk its destruction was used as an index of flash pasteurization (now very rarely used) and is now used as an index of super-HTST pasteurization. 

Significance. Apart from its exploitation as an index of flash or super-HTST pasteurization, LPO is also technologically significant for a number of other reasons ... 

UHT milk differs from pasteurized milk mainly in the heat treatment employed for sterilization. Usually UHT milk is heated at 130° to 150°C for 2 to 8 seconds and is then aseptically packaged. In the final heating stage, steam is injected directly into the milk, or the milk is infused into a steam chamber, followed by flash evaporation to remove added water (steam). An alternative procedure, the indirect method, involves heating milk across a stainless steel barrier, using high-pressure steam as the heating medium (Mehta 1980). 

A quantitative objective measurement of citrus juice turbidity was used by Loeffler (15, 16) to show that pectic enzyme changes occurred so rapidly after the juice was reamed from the fruit that at least a partial coagulation of the cloud occurred before the juice could be screened, deaerated and heated to a pasteurization temperature. He showed that juice turbidity was increased by flash-pasteurization and also by homogenization of the juice before pasteurization. Loeffler (15, 16) presented data on turbidity of flash-pasteurized citrus juices (heat exposure for 16 to 18 sec) after storage at several temperatures. He found that "samples pasteurized at 918C (196°F) lost their cloud when stored at 35°F (95°F) but others pasteurized at 93-95°C (199-2038F) retained their cloud almost indefinitely". 

Citrus juices that are pasteurized at the lower temperatures, 65-66°C, can undergo clarification, i.e., a process of separation that results in a lower layer of liquid and sediment and an upper layer of clear liquid. This process is brought about by the natural enzyme, pectinesterase, that occurs in citrus fruits. Studies have shown that processing of the juice at temperatures of 170-210°F (76.7-99°C) for a fraction of a second to 40 seconds will destroy the pectinesterase activity in citrus juices (7-10). The temperature necessary to stabilize the juice is pH dependent. Juices at higher pH require higher temperatures for stabilization. With the new high-temperature short-time techniques and equipment, stabilization can usually be effected in a fraction of a second. Flash pasteurization can be accomplished in either a plate-type or a tube-type heat exchanger. 

Distillation with vapor product. When a partial condenser is used, the flash drum plays the role of a vapor/liquid separator. In the setup known as a stabilizer there is only vapor distillate, while the liquid is returned as reflux. The column has a pasteurization section when a gaseous stream leaves at the top, while the... 

The trend is toward the third approach of sterile filtration. Almost all wineries use it, though many breweries still prefer flash or "in-the-bottle pasteurization". MF not only removes organisms but improves the clarity of the product. 

The next year Lunde showed that pasteurization at 185° F. in a flash pasteurizer was desirable in that it killed all tuberculosis organisms and at the pump time reduced the bacterial life in the cream to a point at which the butter starter when added would dominate the fermentation. 

Another possibility is flash pasteurization. This consists of heating wine to 90°C for a few seconds and then cooling it rapidly in a high-performance plate heat exchanger. It is considered that this highspeed process is less likely to affect the wine s organoleptic characteristics. 

Fig, 19.21 Continuous tower fermenter, (a) Wort-collecting vessels (b) Impellor-type pump (c) Flowmeter (d) Control valve (e) Flash pasteurizer (f) Tower (g) Yeast separator (h) Beer receiver (j) CO2-Collecting vessel. 

Flash pasteurization is typically carried out in a plate heat-exchanger in which there are four sections (i) a regeneration section, (li) a heating section. 

Fig. 20.33 A typical water deaeration plant involving pasteurization. Equipment for producing chilled, carbonated, deaerated, pasteurized water for beer dilution after high gravity brewing. Alternative systems lead water to the spray chamber either at 15°C or at temperatures above 100°C. In these, the holding tube is omitted. The system with the highest temperature of water relies on flash action within the spray vessel which eliminates the need for vacuum. (Based on diagrams of APV Co., Crawley.)...

Fig. 21.12 Scheme for microbiological control in a bottling or kegging installation [81]. A. Cold-storage tank B. Dosing tank C. Powder filter D. Flash pasteurizer E. Sterile beer tank F. Washer G. Filler. 

Back, W., Leibhard, M., Bohak, I. (1992). Flash pasteurization - membrane filtration. Comparative biological safety. Brauwelt International, 1,42-49. 

The beer-spoilage P. cerevisiiphilus, P. frisingensis, and P. haikarae species have mainly been isolated from spoiled unpasteurized and flash-pasteurized beers... 

Zufall, C., Wackerbauer, K. (2000). The biological impact of flash pasteurization over a wide temperature interval. Journal of the Institute of Brewing, 106(3), 163-168. 

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