I don't have a lot of experience, but I've been thinking about this quite a bit recently. I've been making a tomme (originally from Caldwell's book, but lately trending toward's Linuxboy's recipe: https://cheeseforum.org/forum/index.php/topic,1591.0.html (https://cheeseforum.org/forum/index.php/topic,1591.0.html)) and what I've been really surprised about is how easily the curd knits. My 500g cheese will easily close with 500g - 1kg of weight on it (at most 0.15 psi!) I highly recommend reading through that massive thread, linked above. I think I've learned as much about cheese making there than anything else I've read.
So a couple of things (based on my understanding of the theory rather than my non-existent experience ;-) ). The consistency of the curds depends on the following (among possible other factors):
- The speed of flocculation following adding rennet
- The amount of time you wait before you cut your curds (i.e. the multiplier of the renneting time)
- The size of the curds at cutting
- The temperature of the whey when stirring
- The acidity of the whey when stirring
- The vigour with which you stir
- The amount of time that you stir
"Flocculation" refers to the point at which the milk gets thick enough that it is starting to gel. You can test it by floating a plastic cup in the milk. When you can't spin the cup any more (because the milk has gelled), that's the "flocculation time". There is a youtube video buried somewhere in the thread above showing exactly how to do it. The "multiplier" is the amount of time you wait before cutting the curd as a multiple of the flocculation time. So if it took 15 minutes to flocculate and the multiplier is 3.0, then the total time to cutting the curd should be 45 minutes. However, if it takes 20 minutes to flocculate, then the total time should be 60 minutes. This allows you to adjust waiting times to get consistent results even when your milk changes on you. It's better than the "clean break" test because it is not subjective and is easier to explain.
When you cut the curd is super important. If you cut early, more fat and whey will leak out because the gel is not hard. If you cut late, the curd will retain more moisture and fat. Measuring flocculation time and knowing the desired multiplier will help you determine *how clean* of a break you want (because sometimes it should be super clean and sometimes it should not be clean at all).
Flocculation time is governed by a number of factors: temperature, acidity, amount of rennet, amount of dissolved calcium, the amount of buffering the milk has and probably a number of different factors. I don't really understand the reason, but it seems that faster flocculation times cause drier curd. In linuxboy's tomme recipe, he specifies a target flocculation time of 15 minutes. This allows a fair amount of moisture to be retained (Caldwell, on the other hand recommends a 12 minute flocculation time with a 3.5 multiplier). Anyway, the higher the temp and the more acidic the milk, the faster the rennet will work.
Linuxboy also makes a point that the *drop* in the pH before renneting is vitally important. My imagination of the reason is that the drop in the pH indicates how much of the calcium phosphate buffer has been chewed through by the acid being formed by the culture. Linuxboy recommends that for a tomme you should wait until the pH drops 0.15 before adding the rennet. This is important because it will govern the speed at which the milk will acidify after that point -- and therefore will govern the speed that the milk will gel. The more of a drop you get, the more calcium phosphate has been used up, and the faster the milk will acidify.
Once you have the curd gelled and have your timing set up right, the next is how much you cut the curd. Larger curds will retain more moisture than smaller curds. After cutting, it's important to let the curds "heal" for 5-10 minutes. At that point, if the curds don't shatter, it's a matter of expelling whey. That depends on the temperature, acidity and how much you stir. The more of each, the faster the whey is expelled. However, if the whey is expelled too fast, the outer surface of the curd dries out before the whey inside the curd can move to the outside. This is called "case hardening". When that happens, the whey inside the curd can't get out any more and you are left with whet curds that don't knit well.
So to regulate the consistency of the curd, it's a matter of paying attention to the temperature, acidity, curd size, and how vigorous you stir. The relationship between temperature and acidity is particularly important. The higher the temperature, the faster the cultures acidify the curd (they are still working). However, higher temperatures also expel whey faster, so you are getting a double whammy. You need to plan ahead to think what kind of curd size you want so that they don't shrink too much or too little. You can also vary the amount you are stirring. Less stirring means less whey is expelled.
As the curds shrink, the skin gets harder. At the beginning the curds will squish under their own weight and become an inseparable mass. If you cook for a long time, the curds will be hard and they will need a low of weight to consolidate. If you are trying to get a particular consistency in the cheese, but want the curds to knit under their own weight, then you need to consider that tightrope.
There really are a lot of tricks for consolidating the curds. You can form a mass in the whey and then transfer it to the mould. You can even put the mould in pot and transfer the curds into the mould under the whey.
So having said all that, Gavin Webber's bel paese recipe uses thermaphilic cultures at 42 C and no ripening period. So this means that there is no drop in pH before renneting and therefore we're going for a relatively long flocculation target (which he unfortunately doesn't measure). However, notice that the temp (being thermaphilic) is quite high and so it will acidify more quickly than if we were using a lower temp. The set time is 40 minutes. I'm going to guess that he's going for a 20 minute flocculation time and a 2.0 multiplier. So we expect the break to be a bit sloppy. And in fact it is! But notice that he cuts it anyway and then says that perhaps he should have waited. (I'm not sure if he is correct -- and it would be interesting to speculate the pluses and minuses).
Now he's using a whisk to cut the curds. This will result in a very small curd size. Note, though, that a whisk has fairly large gauge wire. I've found that when I use a whisk and the curds are hard, that the curds tear rather than cut. I *think* that had he waited for a "cleaner" break he would have actually introduced potential problems with that whisk. But because the curds are very soft, they can cut easily with the whisk.
I think we should again be thinking about the rationale here. We've got a long flocculation target, and a short multiplier. We have a high temperature and a small curd size. So we're trying to dry out the curd a bit. However, we have no acidification time, which means that we're being careful not to dry it out *too* much. There is also only a 30 minute cook time. This is going to retain moisture. Thinking ahead, I think what's desired is to cut the curds very small with a soft curd, transfer it to the mould and then let it ripen in the mould. The acidification in the mould will expell whey and since he curd size is small the whey will drain freely. This is why you see the apparent contradiction of everything pointing to a dry curd, but then not pre-acidifying and only cooking it for a short time.
Now on to your problem. The curds are knitting in your pot where they are not knitting in Gavin's pot. Mainly his curds were drier and I'm going to *guess* it's because you "fixed" his "not a clean break problem". However, I hope you can see that there are a variety of different potential solutions and the one you pick will alter the cheese, but maybe in a good way. I don't have enough experience to say what I think you should do, but I hope this gives you some ideas for things you can try yourself..
Mike, a wonderful summary of a number of key issues - well done. I will add a couple of qualifications to your excellent information based on my experience.
Quote from: mikekchar on March 12, 2019, 01:17:41 AM
"Flocculation" refers to the point at which the milk gets thick enough that it is starting to gel. You can test it by floating a plastic cup in the milk. When you can't spin the cup any more (because the milk has gelled), that's the "flocculation time". There is a youtube video buried somewhere in the thread above showing exactly how to do it. The "multiplier" is the amount of time you wait before cutting the curd as a multiple of the flocculation time. So if it took 15 minutes to flocculate and the multiplier is 3.0, then the total time to cutting the curd should be 45 minutes. However, if it takes 20 minutes to flocculate, then the total time should be 60 minutes. This allows you to adjust waiting times to get consistent results even when your milk changes on you. It's better than the "clean break" test because it is not subjective and is easier to explain.
In my experience, the flocc test has proved to be very inconsistent/hard to use with store-bought P&H milk. I had decided that I must be doing something wrong, though for the life of me I could not figure out what--every time I tried, there was never a very clear point of flocculation to set as the flocc time. Then I had the chance to try some raw milk. What a revelation! In more ways than one--but one was that the flocc test actually worked exactly as described. In comparing notes with some other members, it seemed that my experience was not alone. But of course, store bought milk can vary from place to place, brand to brand, so YMMV.
Quote from: mikekchar on March 12, 2019, 01:17:41 AM
As the curds shrink, the skin gets harder. At the beginning the curds will squish under their own weight and become an inseparable mass. If you cook for a long time, the curds will be hard and they will need a low of weight to consolidate. If you are trying to get a particular consistency in the cheese, but want the curds to knit under their own weight, then you need to consider that tightrope.
Though the curds become drier and thus "harder" with greater cooking time, note that temperature also plays a role in how willing curds are to knit. When making a high-temp, low-moisture cheese such as a parmesan, as the temperature rises above around 110°, it becomes very challenging to keep the curds from knitting up, even when actively stirring--if you miss including curds in one area for more than one sweep, they clump up and have to be broken back apart, sometimes with the help of the edge of the cheese ladle. After enough stirring and cooking, they do get dry enough that it is not so difficult. But even then, I find that pressing parmesans (or other thermo cheeses that are pressed before salting) actually requires relatively low pressures to get a good knit - even though dry, the heat in the curds makes them very ready to be cozy with their neighbors. :)