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Old 04-25-2014, 05:23 AM
 
Location: Northern Virginia
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Some comments at this thread about keeping milk from spoiling made me wonder why spoiled milk tastes so bad and is not something we care to ingest, but yogurt (which is apparently spoiled milk?) is edible.
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Old 04-25-2014, 08:28 AM
 
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Raw milk contains many kinds of microbes, with more being introduced depending on its storage and handling practices. Pasteurization dramatically decreases many of these microbes, but not all, thus extending its shelf-life but not indefinitely.

Whether milk spoils, or is converted to a beneficial product like yogurt, depends on the growth of the predominant microbe. This is influenced by growth conditions such as temp, nutrient content, water availability, oxygen content, acidity and concentrations of competitors. By outcompeting its rivals for nutrients, microbes (in the initial stages certain bacteria) alter the composition of the milk due to its production of by-products of growth (acids, enzymes) that can inhibit the ability of other microbes to grow. For example, the produced acids lower the milk pH, which inhibits the growth of other microbes that grow best in more basic (vs. acidic) conditions.

Store bought yogurt is artificially inoculated with high levels of specific bacteria responsible for the conversion of milk to yogurt. Additionally, they are grown in conditions that allows for fermentation, because most of these specific bacteria grow best, or are capable of growth, at very low to zero levels of oxygen. These bacteria feed on the milk sugars and produce acids responsible for the tart taste of yogurt. Historically, yogurt was produced accidentally by storing raw milk in animal stomachs, which contained the right conditions for its formation. In the absence of artificial inoculation or historical milk storing practices, normally stored milk will eventually spoil due to the serial aerobic (presence of oxygen) growth of bacteria and other microbes (mold, yeast), which metabolize the sugars, proteins and fats. The metabolism of the latter two produce by-products mainly responsible for the offensive off-odors and tastes associated with milk spoilage.

Last edited by mingna; 04-25-2014 at 09:49 AM..
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Old 04-25-2014, 10:22 AM
 
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ETA: The specific bacteria (and their by-products) responsible for yogurt formation do not make you ill when ingested; rather, they become beneficial members of your microflora. Other bacteria and microbes (and their by-products) that cause milk spoilage, on the other hand, often also cause gastrointestinal illness. And the offensive off-odors and other visual cues they produce from protein and fat metabolism serve to instinctively prevent one from ingesting it, and possibly getting ill.
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Old 04-25-2014, 10:58 AM
 
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In the United States, for a product to be labeled "yogurt," it must be cultured with Lactobacillus bulgaricus and Streptococcus thermophilus. These are sometimes labeled L. bulgaricus and S. thermophilus respectively. Products in the U.S. labeled as yogurt may also contain other cultures if considered safe to consume but many of the commercial yogurts will only contain the two required ones. Almost all of them will only contain 4-5 in total.

Products labeled as yogurt are made with pasteurized milk, i.e. raw milk that has been heated to very high temps to kill all the bacteria contained in it. Unfortunately, this means all the good bacteria are killed in the process as well as the living enzymes. It is estimated that raw milk contains 50-100 different beneficial species of bacteria. Contrary to popular belief, this started because of the modern mass production of milk where the milk was often contaminated with pathogens. However, in smaller organic or organic-like dairies, pasteurization is not necessary (I could write on a book on this subject but I will resist). The health benefits of raw milk over pasteurized milk are MANY.

At any rate, if pasteurized milk is left out (heated up), it will "SPOIL" because the bacteria that will get a foothold are not the good kind. On the other hand, if raw milk is left out, it will "CLABBER" which is a word for milk fermentation. This basically means the good bacteria will proliferate and culture the milk. The bad bacteria are kept at bay by the good bacteria (mostly Lactobacillus species) and the conditions they create. Clabbered milk is delicious and is like yogurt in consistency, only with about 50-100 beneficial species instead of only two and tastes better than most commercial yogurts. However, it can't technically be called yogurt because it doesn't meet the definition set forth by the FDA.

The temperature does play a part in how well milk of any kind cultures and it depends on which bacterial species are doing the culturing. Some can culture at lower temps while other require a much higher temp. Those who make homemade yogurt sometimes buy expensive incubators to keep the milk at a precise temperature. Lactobacillus bulgaricus and Streptococcus thermophilus both require high temps to culture (110 degrees F I think and higher to begin with). However, raw milk will clabber at a lower temp, often room temp, or by sitting the milk in a slightly warmer spot such as in an oven with a pilot light on or inside an ice chest with a heating pad on low.

Note too: L. bulgaricus is sometimes considered a subspecies of Lactobacillus delbrueckii.
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Old 04-25-2014, 07:32 PM
 
Location: Western Oregon
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Sauerkraut is rotten cabbage. Beer is rotten barley syrup. Wine is rotten grape juice ... whether it's god or bad depends on what microorganisms acted on it, in what environment, and with other variables. Most cheeses depend on the same kind of thing.

Carefully controlled "rotting" is responsible for some of our best foods. Yogurt is the same whey.
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Old 04-25-2014, 07:48 PM
 
Location: Illinois
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Quote:
Originally Posted by WoodstockSchool1980 View Post
Sauerkraut is rotten cabbage. Beer is rotten barley syrup. Wine is rotten grape juice ... whether it's god or bad depends on what microorganisms acted on it, in what environment, and with other variables. Most cheeses depend on the same kind of thing.

Carefully controlled "rotting" is responsible for some of our best foods. Yogurt is the same whey.
Not rotten, fermented. There is a difference.
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Old 04-25-2014, 07:53 PM
 
Location: Western Oregon
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Quote:
Originally Posted by MoonBeam33 View Post
Not rotten, fermented. There is a difference.
My point is that rotting and fermenting are the same thing, in a sense. We use one word if it's seen as a good thing and another if it's seen as bad. I love yogurt, beer, wine and cheese.
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Old 04-25-2014, 10:02 PM
 
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I'd like to add that traditionally sauerkraut, beer, and wine were all fermented with the microogranisms already on the cabbage, barley, and grapes.... much like raw milk clabbers... not by pasteurizing/killing the product first and then adding a few select microorganisms back in...
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Old 04-26-2014, 07:27 AM
 
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Stay on topic of the original post please.
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Old 04-26-2014, 08:47 AM
 
Location: Chicago W Suburbs
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I think this topic is more a matter of semantics than of yogurt. The dictionary definition of both rotten and rancid explains that both words mean tainted, or unpleasant. Since yogurt (in my opinion) is neither, then no, yogurt is not rancid or rotten milk!
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