A warm welcome. A yogurt starter is important. You can't make yogurt without it.... at
least not modern day curd.
The type, quality and amount of culture directly affects the way yogurt:
Whether it's called yogurt culture, starter culture, bacterial culture or yogurt bacteria it's what drives lactic acid fermentation..... the process that changes milk to a delicious curd.
There are 2 types of starter culture available to use at home:
This culture comes from homemade or store bought yogurt.
A homemade starter usually comes from the previous batch.... your own or a neighbors. It should be fresh (less than a week old) so it still contains enough lactic acid bacteria to ferment the next batch.
I confess, in a pinch, I've used yogurt that's 2 to 3 weeks old...... BUT there's the risk of the milk not fermenting properly. Remember lactic acid bacteria decrease with age.
When I use a homemade starter culture, I generally add 1 or 2 Tablespoons extra..... just in case the lactic acid bacteria have declined over successive batches. Your new batch will have the same probiotic bacteria as the starter culture.
A commercial starter culture comes from the container of yogurt you've bought at the store. It should be fresh, unflavoured and not pasteurized after the bacterial culture is added.
The label should state live bacteria or something similar.
A dried culture contains bacteria and milk solids. Basically, it's yogurt that's dehydrated and freeze-dried..... and sold in powdered form. It looks like powdered milk.
The process of fermenting milk with a dried culture is the same as with a fresh culture.
It should say on the package whether the culture is thermophilic or mesophilic. If it doesn't..... look at the bacteria listed on the label.If any of the bacteria are the same as listed in fresh yogurt starter then they're thermophilic.... and should be incubated in warm milk.
Cultures can be either thermophilic or mesophilic.
There are two main lactic acid bacteria used in making commercial yogurt. You can expect to find these bacteria in the brands carried at your grocery store:
Usually L. bulgaricus and S. thermophilus are added at a ratio of 1:1.
Some of the better quality probiotic and organic brands have additional strains of bacteria:
By reading the label you can introduce different bacteria..... this will affect the taste and potential health benefits of the curd. As an example, Stoneyfield yogurt lists 6 strains of lactic acid bacteria on its labels.
Lactobacillus bulgaricus is mainly responsible for the tart taste and smell of yogurt. It produces more lactic acid than S. thermophilus, the other main lactic acid bacteria.
L. bulgaricus grows best at 115 degrees F (46 degrees C) while S. thermophilus does better at lower temperatures. So.....
Keeping the incubation temperature at 115 F will give a tarter yogurt. Lowering the temperature will encourage the growth of S. thermophilus and produce a milder tasting curd.
You can experiment quite a lot....
Whether you're a science buff or a foodie, fermenting milk is interesting. I happen to be both..... so I do LOADS of experimenting with different cultures, methods and recipes. :)
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