In searching for another vein to mine on the subject of “water in food”, I’ve yet to find anything as compelling as cured meats. They (usually) taste good, require some skill to make, look great in photos, and have proven useful for bribing co-workers. More than that, cured meats are excellent examples of how water activity applies to real products. They allow us to see how water activity is affected by salt concentration and drying, and how it relates to product taste and texture.
Still, there’s one product that might be similarly useful and also tasty: cheese. I like cheese as much as the next guy, although a quick trip through the cheese-making blogosphere turned up a recipe for home made Velveeta that I’m unlikely to try. Cheese-making already happens pretty close to where we live – Washington State University is home to Cougar Gold Cheese, a rich white cheddar that the Department of Food Science has been making for decades. The question I have is whether water activity testing can tell us interesting things about cheese during the process of making, molding, and aging.
The one hangup is that cheese is a high-moisture product. Water activity readings work best on semi-dry to dry products. This won’t be a big problem for us, though, because of another instrument my company sells that focuses on that “wet” range of water activity. The instrument is called the WP-4C, and technically, it measures something called water potential. Water activity and water potential are the same thing, just expressed in different units. For people that study water in soil, they’re only interested in the 0.985-1.000 aw range, because any water activity lower than that causes the plant to wilt. Because of that, it’s just easier to use water potential units to discuss plant-usable water.
In any case, the WP-4C will allow us to measure tiny changes in water activity in the high range. It’s accurate to +/- 0.001 water activity units, so even when we’re looking at small changes, we’ll know something has changed.
Like the cured meats, I bought a book on home cheese-making, and I’m in the process of acquiring the equipment I’ll need. First up: farmhouse cheddar, which turns out to be a simplified version of cheddar. Our goals will be the same as with the cured meats: understand how water activity readings relate to product properties like taste, texture, and “done-ness”. We’ll also look at mold growth as a function of water activity, something that is even more important for cheese than it is for cured meats.