Crumbly should be easy! Low humidity will do that.
If the cheese is waxed, larded, or vac bagged, moisture isn't lost into the atmosphere and humidity has little or no effect on the texture. More acidity is the primary way to achieve a drier, "crumbly" cheese. Just cook a little longer before draining or cheddar a little longer so the pH drops to where you want it. I like my cheddar a little smoother, so I don't let the pH drop quite as much. A pH meter really helps with consistency.
Whey contains lactose, which the bacteria "feed on" and convert to lactic acid. Ripening, cooking, draining, washing, cheddaring, and pressing are all tools to control pH and the outcome. When you drain a cheese, you are removing a big portion of the "food" available to the bacteria. Washed curd cheeses like Colby remove lots of lactose. That's why Colby is a milder, smoother cheese than Cheddar. Pressing also removes whey and helps control ongoing acidification. That's why I'm not a fan of extra long pressing times with lower weights. The longer a cheese takes to press, the longer it takes to get out excess whey, and the lower the pH. If it's a brined cheese, then the cheese has a much longer time to acidify before brining.
