What aging does to a hard cheese

Set a young cheddar beside a very old one and the gap between them can seem too wide for one kind of cheese. That gap comes from slow chemistry inside the wheel. The University of Guelph's cheesemaking e-book, by Arthur Hill and Mary Ann Ferrer, calls ripening the breakdown of proteins, fats and carbohydrates. That breakdown frees flavor compounds and changes the texture. The authors admit the process is only partly understood. They also give the range, from nothing at all for fresh cheese to five years or more for some hard cheeses.

Protein does most of the work

Casein protein gives cheese its structure, so when it comes apart, both taste and texture move. Hill and Ferrer describe three steps. First, enzymes called proteases cut proteins into small pieces called peptides. Some of those already have a taste, and bitter and brothy ones are well known. Next, other enzymes cut the peptides down to amino acids. Last, microbes in the cheese turn those amino acids into acids, aldehydes and sulfur compounds, and many of these taste good. In Cheddar, the Guelph authors say flavor and texture depend mainly on this protein breakdown and much less on fat.

Several things share this job. The milk brings its own enzyme, plasmin, which survives pasteurization. The rennet that set the milk keeps acting on the protein too. Starter bacteria add more enzymes as they die. Guelph gives a number for Cheddar. These bacteria can reach 500 million per gram in three or four days and fall to about 20 million by four weeks. The dying cells release enzymes that keep ripening the cheese. Other bacteria from the milk and its surroundings grow in their place.

How far all this goes is easy to underestimate, and work from Italy puts a number on it. Researchers at the University of Milan report that free amino acids make up more than 20% of the protein in hard cheese after 10 to 12 months. Guelph says protein breakdown leaves a cheese less rubbery, less elastic and easier to melt. Too much of it goes wrong, though. The same chapter lists bitter, putrid and brothy notes as the faults that follow.

Fat and sugar play smaller parts

Butterfat holds a lot of flavor because it carries an unusually wide mix of fatty acids. Guelph calls it the only natural fat rich in short chain fatty acids. One of them, butyric acid, is potent and needs to stay in balance with everything else. Enzymes set these fatty acids loose in a process called lipolysis. Microbes can then change them into other flavor compounds. Some styles lean on this more than others. Blue molds do a lot of it, and goat milk cheeses tend to show more of it. The main fat enzyme in milk dies with low heat, so it counts for most in raw milk cheese.

Milk sugar has the least to do with how an old cheese tastes. One day after making, most of the lactose has left in the whey or turned into lactic acid. In Cheddar, Guelph puts what remains at 0.3 to 0.7% on day one. It falls slowly to under 0.1% with age. Next to fat and protein, the authors rate its flavor role as minimal.

Losing water changes everything else

Water affects all of this chemistry. Guelph's rule is that a moister cheese ripens faster, with more chance of off flavors. Temperature pushes the same way. Firm and hard cheeses usually ripen at 10 to 15 C, or about 50 to 59 F. Cheddar often starts colder, at 4 to 6 C for several weeks, to hold back early bacterial growth. The authors add a general warning. Anything that speeds up ripening raises the risk of off flavors and shortens the time a cheese is good to sell.

What goes around the cheese matters too, and cheddar shows it best. America's Test Kitchen quotes Dean Sommer of the Center for Dairy Research at the University of Wisconsin-Madison on this. Block cheddars age in plastic and hold their moisture. Bandaged wheels keep drying, and oxygen reaches them and changes how flavor forms. Yeasts, molds and bacteria also grow on the rind.

Two makers give numbers for that drying, and they show how much it can vary. Face Rock Creamery in Oregon makes both kinds of cheddar. It says its clothbound wheel loses about a tenth of its weight in 13 months and ends up with the moisture of a parmesan. That drying is why it tastes drier and sharper than a block of the same age. Shelburne Farms in Vermont reports a bigger loss for clothbound in general, at 15 to 20% of body weight. It adds that its cave runs warmer and wetter than a normal aging room, which also affects how fats and proteins break down.

Where the crunch comes from

Those small crunchy specks in an old wedge are a direct result of everything above. In culture magazine, the cheese scientist Pat Polowsky explains that tyrosine and leucine are two amino acids set free as casein breaks down. They build into crystals in aged gouda, Parmigiano Reggiano and Alpine styles. Guelph says tyrosine crystals can reach 2 millimeters. The white haze or flecks on aged cheddar are usually a different crystal, calcium lactate. It forms when lactic acid pulls calcium out of the casein and both build up.

The Milan group ties the crystals back to water, since less of it can hold less in solution. As the water drops and amino acids and salts pile up, crystals come out. Both Polowsky and the Milan team say crystals do not directly add flavor. Polowsky's useful point is that they mark protein breakdown. Seeing them tells you the cheese has had real ripening time .

Older does not always mean better

Age on a label is only a clue, because makers judge their wheels one batch at a time. Wisconsin Cheese says Uplands tests each batch of Pleasant Ridge Reserve, since each one matures at its own pace. Only a small number of wheels go past a year and sell as Extra Aged. America's Test Kitchen says the same about cheddar. Makers test their cheeses to decide how long to age them, and one batch may turn out with a better crunch than the last. Jasper Hill Farm lists a range of 9 to 14 months for Cabot Clothbound rather than one fixed number, and it brushes, turns and checks the wheels along the way.