Why didn't my ricotta curdle?

Question

I've been making my own yogurt for a while – 1-2 quarts of whole milk, 12 hours cooked, into 1-2 pints after straining it all day. A few batches ago I started saving the whey. Today I tried to make ricotta from it: I heated the whey (one big pickle jar, probably about 24oz but I didn't measure, plus the extra whey from today's one-quart batch). Heated it on the stove to 195 F, added vinegar, stirred it, left it for a while, no visible curdling happened. Poured it through a strainer with a lot of layers of cheesecloth on it, the liquid that came through was about as cloudy as it was at the start and there were no curds I could see.

Any idea?

Answer 1

According to the US Department of Agriculture's FoodData, there is 0.76 g of protein in 100 g of acid whey (whey from drained yoghurt; whey from cheese production is "sweet").

According to the same source, a quart of acid whey weighs 984 g, so 24 fl oz weighs 738 g, and therefore contains 5.6 g or 0.2 oz of protein total. Even if none of it passed through your cheesecloth, that might not be enough curds to see; in any case, you'll need a lot more whey before the process is worthwhile.

Sweet whey is not much better at 0.85 g / 100 g; usually when people talk about making ricotta at home they are actually making some other type of fresh cheese from whole milk rather than whey. Real ricotta is almost always a by-product of making other cheeses in far larger amounts.