My understanding is that yoghurt is is the biproduct of a yoghurt culture, a bacteria, eating lactose and excreting the yoghurt.
My question is – why does it need to be lactose that the yoghurt culture is eating?
For yeast to produce alcohol, for example, the yeast can eat any sugar, and it's up to the brewer to decide whether that's sucrose, corn, barley, grapes etc to affect the taste.
Why is that that yoghurt cultures need lactose specifically?
Best Answer
Lactobacillus is the genus of the bacteria responsible for making yogurt.
These bacteria consume sugars and excrete lactic acid. The acid denatures the proteins in the milk, causing them to coagulate into a delicious gel.
Lactobacilli can consume sugars other than just lactose.
https://en.m.wikipedia.org/wiki/Lactobacillus
The reason they eat lactose when making yogurt is because that's what they have. There is more than enough lactose in milk to make yogurt. There's no reason to add other sugars.
Lactobacilli are also responsible for the fermentation of pickles. In that case, even though they still produce lactic acid, they are consuming the sugars available in the vegetables, not lactose.