The current make notes that I've posted in some other threads use a floc of 3.5, so if one were to reduce that to say, 2.75 or 3, that would be the first change. To build up the acidity, I would suggest increasing the amount of time during the cheddaring stage (after draining the whey, keeping the curd cake warm in the pot) to something like 2 hours, flipping and stacking the curds every 20 minutes or so. The other possibility is to also increase the cooking time before draining the whey as well.
I would not do a big jump on the floc so I would go with 3 for a drier cheddar. Learning to make THE cheese that you want is trial and error sometimes, and you don't want to change more than one variable at a time or you won't know what worked, or didn't work for you.
Acidity is going to be your biggest change factor for "crumbly" anyway. Cheddars are the one category of cheese that I won't make without a reliable pH meter. I have done enough cheddars now that I can tell by feel when a curd mass is approaching the correct pH range. The curds will start sticking together much more aggressively and become more difficult to mill or break apart. But I always use a meter to get more consistent results. Otherwise your finished quality will be all over the place. And it's not just the pH at salting/hooping or the pH of the finished cheese that counts. You should drain traditional cheddars at around 6.1, so you do NOT want to keep cooking to reach the desired salting pH. That will just make your curds drier and harder to meld in the hoop. Cheddar as long as it takes to reach your terminal pH. Depending on the cultures that you use, that will take more or less time, so this is a great example of why simple time based recipes don't give the best results.
I do 5 different English Cheddars - Cheshire, Derby, Gloucester, Lancashire and Wensleydale. I salt Cheshire at 5.4 and I salt Wensleydale at 6.0. The others are in between. The Cheshire is dry and crumby. The Wensleydale (which uses an Aromatic meso culture) is much sweeter, creamier, and easier to slice. I actually do a partial washed curd on the Wensleydale to reduce the acidity even more.
Over time, acidity is generally balanced out with aging and the pH actually goes back up. However there are a few hard cheeses that are traditionally eaten young and can benefit from some creative pH management. Caerphilly and Lancashire come to mind first. When eaten young, both of these cheeses are acidic and tart. My English customers love them that way, but many Americans do not. So you can control both the early and longterm outcomes by simply adjusting starter, draining sooner, washing the curds, and/or hooping at higher pH.
