|MadSci Network: General Biology|
A few clarification and a few answers... Yogurt should NOT contain yeast. Yeast are different than bacteria. They are actually more closely related to you and me than they are to bacteria! By "lactic ferments" I think you mean lactic acid bacteria. Freezing does kill bacteria, but not 100%. This is why frozen chicken still needs to be cooked. It may still contain Salmonella bacteria. Depending on many factors (age of yogurt, speed of freezing, etc.) frozen yogurt may still contain viable (i.e. alive) bacteria. So it's possible, even likely, that frozen and thawed yogurt will contain living lactic acid bacteria, although it may only be 10% or 1% of the total number of bacteria that were there before the yogurt was frozen. Since the yogurt is already quite acidic, and the yogurt would not "develop new cultures" upon thawing, however if those thawed bacteria were placed into fresh milk, at warm temperatures you might be able to make more yogurt out of that milk, but it might not be as good as the original yogurt (because of contaminating bacteria from the milk or your kitchen, or because the ratios of the two or three different yogurt bacteria have changed after freezing).
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