Oh, and I discovered this today as I went to make some mozzarella.
Some cheese you can kinda wing it and not worry too much about the pH. Hole-less swiss seems to be one of those, it tends to be much less prone to error. Mozzarella on the other hand is not. If you want a good moz, your milk must be at 5.2 pH otherwise it usually just won't work.
Undaunted by this very real fact--a fact that I have confirmed many, many times by screwing up moz, I decided to go ahead anyway. This cheese consisted of 1 gallon 1% milk, 2 teaspoons of citric acid, 1/4 teaspoon of rennet, and 1/8 teaspoon of calcium chloride. The heating schedule was to combine all ingredients except rennet while the milk was cold, heat to 88F, add rennet, heat to 105F, then cut and drain. After that point you microwave the curds for 30 seconds at a time to extract more whey, until the curds are 130F. At that point, you should be able to knead and stretch the curds like taffy.
I knew something was a little off when at ~70F the milk was already coagulating. This meant I added to much citric acid, but from previous experience I knew this wasn't a dangerous amount of coagulation. I was probably at the upper limit of acid, but as long as it remained *mostly* liquid before I added the rennet I should be okay.
By the time I hit 88F, I thought I was doing pretty good (and in hindsight I was). I added the rennet, put the pot in a hot water bath, and slowly raised the temp to 105F. When I cut the curd I noticed that the curds were a bit grainier than they should be, but during draining they firmed up really well. Yet another sign of too much acid, but nothing to be done at this point.
When they curds are drained, the basic schedule for making moz is to microwave the curds for 30 seconds, drain off the whey, and flip the curds. Repeat this about four or five times till the curds become stretchy. If the curds disintegrate into grains then you are waaay to acidic. If you never get any stretch you are too base. I don't know of any way to correct this problem at this stage other than feeding the curd to your dog and starting over.
With this batch, it got stretchy, but not as stretchy as I wanted. It was still kinda grainy looking, but I could actually shape it into a nice looking ball. After kneading the cheese for a minute or so, I plunged it back into the saved whey with salt and put it into the fridge.
After sampling it, I can say I think this is the secret to 'firm' mozzarella. If you push the pH just a tad more acidic, you still get the texture and form of mozzarella, but it is much denser. I did some tests and it is also an excellent melter, and has a nice flavor to boot.
What to do with this kind of cheese?
If you are making mozzarella for a pizza, and only have a conventional oven that can get to 500-550F, making the moz with a pH of probably 5.1 should give you a good melter that won't make your pie soggy.
I love a good, creamy, wet mozzarella, but for home cooks in conventional ovens it's kind of a nightmare. I haaaaate it when a pizza is perfectly cooked on the edges, but still mushy in the middle. HATE HATE HATE!!! But I also hate store bought firm mozzarella, since it is always so salty. HATE HATE HATE!!! But this accident may have opened my eyes to a third way to get great cheese results in a regular oven, with a great subtle mozzarella flavor and no sogginess.
I'll report back with more findings :D