Everything seemed to be normal up until the step where you microwave the cheese curds. Instead of melting together into an elastic ball of yummy mozzarella, the curds kept breaking into smaller and smaller grains, close to the consistency of ricotta. We kept checking the temperature of the cheese with an instant-read thermometer, and we were definitely getting it hot enough.
The cheese became a little firmer and more cheese-like after we gave up and let it sit for a while, but trying to microwave it again didn't do anything. It was still delicious on pizza, but just not quite what we were going for.
We have a few theories about what might have happened:
1. We did one step differently than the previous time: after adding the rennet and letting it sit, we re-heated the curds and whey to 105° while stirring gently. This was a step in the booklet that came with our kit that we skipped the first time because a note later in the booklet and an instruction on the company's website both said this step was optional.
2. We didn't have a good spoon for scooping the curds out of the whey. As a result, the curds became more broken up and we scooped up a fair amount of whey along with the curds. In our first cheese-making experience, we were able to drain off the excess whey as the cheese came together. This time, it seemed like the whey mixed back in with the curds and made it soupy.
3. Our milk was old, as in a day before the expiration date. We're not sure if this would affect the cheese-making, though. By the way, the milk was definitely not ultra-pasteurized.
4. We accidentally used an aluminum pan. Aluminum can react with the citric acid to create an off-flavor and discoloration, but we also wonder if it might have interfered with how the curds formed. Since everything seemed fine up until the microwaving stage, we're thinking this wasn't the problem. But you never know... (P.S. As far as we could tell, our resulting ricotta tasted and looked fine!)
Our best guess is that we stirred the curds too much, both during the re-heating stage and during the scooping stage. We're not sure why this would make such a difference - you'd think the cheese would just come back together after being heated in the microwave - but the company mentions over-stirring as the culprit behind a few different cheese-making mishaps.
Next time, we'll go back to skipping that re-heating step and maybe try upping the amount of citric acid.
Related: Top Five Things to do with Ricotta
(Image: Emma Christensen for the Kitchn)