I know a big deal has been made out of pH, and rightly so. It's a very useful indicator. But the truth is that there are many valid pH ranges for a cheese style and that pH is an indicator of what's going on underneath the surface. The truth is that for just about all cheeses, there are 3-4 valid ranges for the critical points, and its important to know what they are and more importantly what they represent. Time is also important, so is temp. pH is more useful as an indicator for when something has gone wrong and needs adjustment for the final recipe, and as a quality control point. It shouldn't be used as a sole criterion for making decisions.
In general, when using a standard 1 U/DCU per 50 liters:
The pH at adding rennet should be about 6.5. Normally, it will be around here anyway, unless your milk is off. Very fresh milk may be slightly higher. Goat's milk may be slightly lower.
The pH at draining whey varies with the cheese style. For cheeses that have a high final calcium content, and very little micelle degredation, the pH is 6.2-6.4. These cheeses are the alpines and high heat thermophilic. They also include tommes. For cheeses that have moderate calcium content, this is the vast majority of cheese, the pH range should be 6.0-6.25. This is when you should drain whey and start packing the curds together, either under the whey, or in the mold. Typically, you want a moderate amount of calcium content so the curds fuse together well. For ladled cheeses, like brie, same thing, you "drain" at 6.0-6.1.
Next key aspect is the pH at salting or brining or other action. This should just about always be 5.4. The exception are lactic cheeses and cheeses that need lactic acid to feed mold, like bries and blues. You mill and salt cheddar at 5.4. You brine a tomme at 5.4. The 5.4 is important because it represents the point where a moderate amount of acidity has built up. You need this acid to help preserve the cheese, for the cheese body, for proteolysis, etc.
Last aspect is more of an aside, and it is pH at finish, right out of the mold. For lactic and blue/brie, this should be 4.6-4.8. It should be that because this is the point where milk precipitates and all the charge on the micelles has been neutralized. This means enough acid has been built up to ensure the cheese ages properly and the mold eats the lactic acid evenly, not forming too dry or too liquified of areas.
The drain pH influences the final pH, because at drain you are removing easily available lactose, yet some lactose is trapped in the curd.
If you need pH numbers for a recipe, just post. But for all the talk about pHs importance, it's more important to pay attention to the key tipping points I just wrote about. I've posted before more about the science and what happens at those tipping points if you want to read more.
