What exactly is overworking the curd?
What effect does the manner and timing of salting have? I mean that if I hit the target ph of 5.4 (this is in the whey not curd, right?) at the end of cheddaring, and I begin salting, is there a lot of variation depending on how I salt? e.g. 3 rounds of adding salt at ten minute increments, 1 big dump of salt and then mix, or other approaches.
I was making jack this past week using my new ph meter and was at the point right before adding cold water to drop the temp after cooking the curd. The ph finally was 6.21 and I started draining the curd and I decided to monitor the ph while I was draining and the bottom just fell out. I was at 5.8 before I could get the whey down to the curd and start adding water. I was not expecting that kind of rapid change either. Are the points that linuxboy pointed out as the most critical also the most difficult to manage? It seems that I need a quicker method of whey draining.
Overworking the curd causes curd shattering. You experienced this when your ice cream mixer was going at too many RPMs. Like Ben said, fat is released and you will get a dryer cheese. Healing curd before stirring helps to minimize shattering.
Manner and timing of salting has to do with hitting a final salt content in the cheese. For example, if you dump all the salt in at once, it will help the curds expel more whey. Well, all that whey will wash away some of the salt and the final internal salt percentage will be less than if you salted at 5-10 min increments. Commercially, incremental saltging is most often used for practical reasons. The curds need to be coated evenly, so a third or half the salt is spread out on top, the curds are tossed with a large pitchfork, which takes 5-10 mins, and then more salt is added. For home application, I suggest the same approach. You want even salt coverage in at least two applications. Let the whey drain after salting, pour it out, toss the curds, and add more salt.
Yes, target pH is of whey at the closest point possible to the curd. Meaning whatever liquid the curd expels. You couldn't accurately measure actual curd ph, anyway. To do that, you'd need to pulverize the curd and use an emulsifier, then measure. If you press the pH meter to the curd, you'd be testing the pH of the whey that the curd expels, vs the whey in the pot. There is a slight difference in that the whey leftover acidifies faster than in the curd.
The interesting pH behavior you experienced with the jack most likely has to do with the water addition or the acidification rate of your starter. Milk has a lot of buffers in it. If you add water, the buffer capacity may be decreased as ions come out of solution (this is less likely), leading to a faster drop. Another possibility is that your starter acidifies faster after it hits a pH of 6 (this is most likely). The way you figure this out is to look at the acidification curves. If you don't have one from your supplier, ask for it, or make one yourself by plotting pH vs time in a cheese. If for a normal, non-washed cheese the acidification is more steady, then you know it was the water that led to the drop.
Just another quick note... you could drain whey earlier than 6.2, but in most cases, it is impossible unless you make the curd very small and heat up quickly. By the time you can drain whey, the pH will likely be 6.1-6.2. If it's less than that, use less starter next time, and hurry up and finish draining
Ben, ambient room temp influences knitting in the mold and acidification post drain. Of these, the knitting or lack of it contributes to crumbliness. If the temp is lower, you need more weight or to press for longer for the curds to knit. If your curd was at 80 degrees for knitting and cheddaring, you're doing well. Commercially, the vats are heated while cheddaring takes place.
Ideally for most styles, what you want is to knit the curds well together right away (that initial hour while the curds are hot is crucial) but without using too much weight or the water content will not be the same throughout the cheese, then let the cheese sit for a bit so the remaining lactose can be digested. If there's too much lactose, other bacteria can eat it and the cheese has less preserving capacity.
Phew. long post.