Where did the bacteria that turn milk into yogurt come from? Have they evolved since humans started to store milk? If so, what did their forebears do? (continued)
Christina Sommerville
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Stirling, UK
A previous reply to this question identified several bacteria which 鈥渇erment the milk sugar lactose to lactic acid, which sours milk and coagulates milk proteins鈥�.
However, I have made yogurt approximately twice a week for some time now using semi-skimmed, lactose-free milk. I use a culture from a commercial, natural bio live yogurt containing Bifidobacteria, Lactobacillus acidophilus and Streptococcus thermophilus. The end product is indistinguishable from other plain yogurt. I wonder what these bacteria are feeding on.
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