Can whey from strained yogurt be used to inoculate milk for a new batch of yogurt

Question

I’m using 1/2 gallon of whole milk to make yogurt. How much whey to add to make yogurt

Answer 1

When making yogurt (a gallon at a time), I use one ice cube of frozen yogurt from a previous batch as the starter. The frozen yogurt cubes work even after being frozen for months.

If I'm getting low on cubes, I pour some of the freshly inoculated gallon into an empty ice cube tray. After it has cultured, I put it in the freezer. Once frozen, the cubes go in a ziplock bag and I'm good for another 12 yogurt batches.

And so on. I haven't bought starter for years.

I did originally have difficulty finding a commercial yogurt with enough viable bacteria to function as a starter. I believe most commercial yogurt is pasteurized a second time (after culturing) to extend shelf life. This kills enough bacteria that the yogurt doesn't function as a starter. After failing with 6 different yogurts, I found one which has worked well: Tree Island, a boutique yogurt.

In Canada, if a yogurt is labelled "Probiotic", it is required to have a certain concentration of viable bacteria in it. A few years ago, about half of all yogurts bragged about being "Probiotic", but not any more. My suspicion is the price premium for displaying the "Probiotic" label did not outweigh the cost of the shorter shelf life.

Answer 2

Using whey from strained yogurt can work as a starter culture, but maybe not as predictably. This is because whey usually has lower concentrations of cultures than the thick yogurt itself. This lower bacterial count might result in longer incubation times, less tang, or a thinner consistency. If you have yogurt on hand, it's probably better practice to stir some of that in. For 1/2 gallon of milk you wouldn't need that much, maybe a tablespoon or two.