What a great mistake. No need to cook further to make it safe for eating. Cooking at 90deg will have already pasteurised the milk so that your yoghurt culture can grow without competition.mkr I only cook it on 80deg
Quote from: andiesenji on May 04, 2010, 04:27:11 pmAs I mentioned in an earlier post, as did Thermomixer, there is a chemical change in the milk after the pre-heating to a specific temperature, that allows the yogurt culture to change the structure of the milk solids - the casein proteins, of which there are four types in cow's milk. Without this process the culture can't "invade" the cells efficiently and there is the possibility that an undesirable organism (that is less fussy about the structure of the milk proteins) can propagate and produce what you describe as a "slimy" end result.Pasteurization does not kill ALL the bacteria in milk. There are always some organisms that are not exactly pathogenic but are also undesirable. Without the heating to a high enough temp to inactivate these organisms, you will give them an opportunity to take over and actually prevent the development of the desirable bacteria.Following is a quote from the California Milk Board:"Yogurt is formed by the growth of two bacterial organisms in milk; Streptococcus thermophilus and Lactobacillus bulgaricus which turn the milk sugars into lactic acid. These are two separate bacteria that are active at different times during processing. Some times you will also find yogurt that contains other ""Probiotic"" cultures such as Lactobacillus acidophilus, Bifidobacterium longum, and Bifidobacterium infantis which are bacterium normally found in your intestines. Together these bacteria aid in digestion and the synthesis of vitamins. Here are the required steps. Heat milk to between 180 and 200 °F. Heating the milk is done for a few reasons. First, to sterilize/pasteurize the milk so that the yogurt bacteria/culture has a hospitable place to grow in. It is not desirable to incubate contaminating bacteria that might be present in the unsterilized milk. Heating should be done even with pasteurized milk to help make a smooth thick yogurt. Heating the milk also helps stop the whey from separating out quite as much. You must then cool milk to 115 °F and add yogurt culture. (If the milk is too hot it will kill the yogurt bacteria.) Stir in yogurt culture gently until dissolved. Hold temperature at 105 to 110 °F for approximately 8-10 hours. This allows your ""good"" bacteria to grow. The methods listed in the post are suitable for this. Finally, you must refrigerate the processed yogurt for at least two hours. Refrigeration help slow the continued bacterial growth. If yogurt is not refrigerated it will become sour."and:The whey proteins are more sensitive to heat than the caseins. HTST pasteurization will not affect the nutritional and functional properties of the whey proteins. Higher heat treatments may cause denaturation of ß-lactoglobulin, which is an advantage in the production of some foods (yogurt) and ingredients because of the ability of the proteins to bind more water. Denaturation causes a change in the physical structure of proteins, but generally does not affect the amino acid composition and thus the nutritional properties. Severe heat treatments such as ultra high pasteurization may cause some damage to heat sensitive amino acids and slightly decrease the nutritional content of the milk. The whey protein α-lactalbumin, however, is very heat stable.
As I mentioned in an earlier post, as did Thermomixer, there is a chemical change in the milk after the pre-heating to a specific temperature, that allows the yogurt culture to change the structure of the milk solids - the casein proteins, of which there are four types in cow's milk. Without this process the culture can't "invade" the cells efficiently and there is the possibility that an undesirable organism (that is less fussy about the structure of the milk proteins) can propagate and produce what you describe as a "slimy" end result.Pasteurization does not kill ALL the bacteria in milk. There are always some organisms that are not exactly pathogenic but are also undesirable. Without the heating to a high enough temp to inactivate these organisms, you will give them an opportunity to take over and actually prevent the development of the desirable bacteria.Following is a quote from the California Milk Board:"Yogurt is formed by the growth of two bacterial organisms in milk; Streptococcus thermophilus and Lactobacillus bulgaricus which turn the milk sugars into lactic acid. These are two separate bacteria that are active at different times during processing. Some times you will also find yogurt that contains other ""Probiotic"" cultures such as Lactobacillus acidophilus, Bifidobacterium longum, and Bifidobacterium infantis which are bacterium normally found in your intestines. Together these bacteria aid in digestion and the synthesis of vitamins. Here are the required steps. Heat milk to between 180 and 200 °F. Heating the milk is done for a few reasons. First, to sterilize/pasteurize the milk so that the yogurt bacteria/culture has a hospitable place to grow in. It is not desirable to incubate contaminating bacteria that might be present in the unsterilized milk. Heating should be done even with pasteurized milk to help make a smooth thick yogurt. Heating the milk also helps stop the whey from separating out quite as much. You must then cool milk to 115 °F and add yogurt culture. (If the milk is too hot it will kill the yogurt bacteria.) Stir in yogurt culture gently until dissolved. Hold temperature at 105 to 110 °F for approximately 8-10 hours. This allows your ""good"" bacteria to grow. The methods listed in the post are suitable for this. Finally, you must refrigerate the processed yogurt for at least two hours. Refrigeration help slow the continued bacterial growth. If yogurt is not refrigerated it will become sour."and:The whey proteins are more sensitive to heat than the caseins. HTST pasteurization will not affect the nutritional and functional properties of the whey proteins. Higher heat treatments may cause denaturation of ß-lactoglobulin, which is an advantage in the production of some foods (yogurt) and ingredients because of the ability of the proteins to bind more water. Denaturation causes a change in the physical structure of proteins, but generally does not affect the amino acid composition and thus the nutritional properties. Severe heat treatments such as ultra high pasteurization may cause some damage to heat sensitive amino acids and slightly decrease the nutritional content of the milk. The whey protein α-lactalbumin, however, is very heat stable.
Author
Topic: yogurt (Read 6828 times)