On Mon, Oct 6, 2008 at 7:47 AM, ss <[EMAIL PROTECTED]> wrote: > UHT yogurt is sterilized. "Natural" yogurt should have culture in it.
Quoting relevant bits from the book 'On Food and Cooking: The Science and Lore of the Kitchen' [1] that I am currently reading (highly recommended book): "Pasteurization extends the shelf life of milk by killing pathogenic and spoilage microbes and by inactivating milk enzymes, especially the fat splitters, whose slow but steady activity can make it unpalatable. Pasteurized milk stored below 40 F/5 C should remain drinkable for 10 to 18 days. There are three basic methods for pasteurized milk. The simplest us batch pasteurization, in which a fixed volume of milk, perhaps a few hundred gallons, is slowly agitated in a heated vat at a minimum of 145 F / 62 C for 30 to 35 minutes. Industrial-scale operations use the high temperature, short-time (HTST) method, in which millk is pumped continuously through a heat exchanger and held at a minimum of 162 F / 72 C for 15 seconds. The batch process has a relatively mild effect on flavor, while the HTST method is hot enough to denature around 10% of the whey proteins and generate the strongly aromatic gas hydrogen sulfide. Though the "Cooked" flavor was considered a defect in the early days, US consumers have come to expect it, and dairies now often intensify it by pasteurizing at well above the minimum temperature, 171 F / 77 C is commonly used. The third method of pasteurizing milk is the ultra-high temperature (UHT) method, which involves heating milk at 265-300 F / 130-150 C either instantaneously of for 1 to 3 seconds, and produces milk that, if packaged under strictly sterile conditions, can be stored for months without refrigeration. The longer UHT treatment imparts a cooked flavor and slightly brown color to milk... Sterilized milk has been heated at 230-250 F / 110-121 C for 8 to 30 minutes; it is even darker and stronger in flavor, and keeps indefinitely at room temperature." And while we are on this topic, what Indians call curds is not really curds, it refers to fermented milk - i.e. yoghurt. Curds and Whey (as in the nursery rhyme 'Little Miss Muffet') are two groups of proteins (caseins and whey proteins) in milk that react differently to acids. Thaths [1] http://www.amazon.com/Food-Cooking-Science-Lore-Kitchen/dp/0684800012 -- "I saw this in a movie about a bus that had to SPEED around a city, keeping its SPEED over fifty, and if its SPEED dropped, it would explode. I think it was called, 'The Bus That Couldn't Slow Down'." -- Homer J. Simpson
