How Cheese is Made Part II: From Milk to Curd

milk to cheese curd, cheesemaking Previously: How Cheese is Made Part I: Milk


How does milk become cheese? The process of converting milk into cheese is complicated but not as mysterious as it may seem. Simply put, making cheese is the process of concentrating the suspended solids in milk and turning them into something that can be easily preserved....while at the same time remaining pleasant tasting and convenient to eat. For the longer answer - keep reading.


If the name Louis Pasteur is familiar, it's because he's the man who invented the process named after him, pasteurization. Pasteur pioneered the idea of heating certain liquids like milk in order to kill potential pathogens.

Milk, taken straight from the animal, is considered a raw product. Once it has been treated with heat according to a variety of possible protocols perfected since Pasteur's time ( I won't bore you with the details here but go to the end of this post for a list of resources for further research) it is considered pasteurized. Some cheesemakers make cheese from raw milk, some from pasteurized, some from both.

You're probably already familiar with the heated arguments that surround raw milk production and consumption. In short, some believe that pasteurization destroys beneficial enzymes and bacteria inherent in fresh milk; others believe that safety requires pasteurization. Raw milk is regulated on the state level and its availability varies from region to region. In Washington, dairies may produce and sell raw milk if they are specifically licensed to do so. In Oregon, dairies may produce raw milk under certain very specific conditions (they may only milk up to three cows, they may not advertise sales of the milk). In any event, the arguments for and against raw milk and raw milk cheese are legion, and I will leave you to make decisions on that issue for yourself.

In both the United States and Canada, the law allows cheesemakers to sell cheese that's made from raw milk only if the cheese has been aged for at least sixty days. The idea behind the so-called 'sixty day rule' is that any potential lurking pathogens in raw milk - not that there are any necessarily, but if there are -  will have degraded after sixty days, at which point the cheese is considered by law safe to consume. There is much controversy in the cheese world about this rule; many cheesemakers and cheese aficionados feel that cheese made from raw milk is superior to cheese made from pasteurized milk.

The Transformatory Power of Cultures and Rennet

How do you turn milk into cheese? Two of the most important tools in a cheesemaker's toolbox are bacterial cultures and rennet. While there are as many cheese recipes in the world as there are cheeses, step #1 of the cheesemaking process usually involves the addition of bacterial cultures to milk. The importance of bacterial cultures to cheesemaking is vastly underappreciated by most people. Cheese cultures have a profound effect on the finished product, in fact, a cheesemaker can order cultures specific to the cheese that they want to make: so, for example, a cheesemaker will order gouda cultures to produce Gouda, a set of cheddar cultures for cheddar - you get the idea. A cheesemaker can hand pick cultures that will give a cheese more holes like swiss cheese, or make it taste more rich and buttery. Some cultures work in the presence of heat, some don't. So important are cheese cultures that, in some cases, their identity is a closely guarded proprietary secret - like the cultures that go into WSU Cougar Gold, which were first developed in the 1940s.

Once added to milk, cultures work their magic for a period of time that depends on the particular recipe involved. After that process is complete, the cheesemaker adds rennet. Rennet is really a collection of enzymes that act as coagulating agents, turning milk to the consistency of silky white custard. There are several types of rennet available for use by cheesemakers. Traditional rennet is derived from the lining of the stomach of calves. More recently, science has developed bacteria which are genetically engineered to manufacture rennet - so called GMO rennet. Cheesemakers may also use microbial rennet or thistle rennet, the latter a coagulating agent derived from thistle plants and used in Spanish and Portuguese cheeses (for more specifics on the various types of rennet see here).

Curds & Whey

And so, assisted by the carefully coordinated effort of cultures and enzymes and sometimes the application of heat, the cheesemaker's milk will separate into solids (curds) and liquid (whey). At this point, the cheesemaker will typically cut the curd into small pieces, maximizing the release of whey.

curds and whey

From here, a cheese recipe can take a variety of paths....the cheesemaker could simply drain the whey and be done, if she's making a fresh cheese like chévre or fromage blanc. Washed curd cheeses might be made by draining off the whey and gently washing the curds in a variety of substances like hot water or even beer....Gouda cheese is one example of a washed curd cheese. A cheesemaker might also heat the mass of curds and whey before draining off the whey, as is also done in the process of making Gouda (heat helps to drive more moisture out of the cheese curds, producing a final product that is more dense and uniform). Cheddaring is another option - a labor intensive process of piling, stacking and re-stacking cheese curd which causes the cheese curds to knit together and, cheesemakers say, is what makes cheddar cheese unique and so good.

Whey: What is it Good For?

What happens to all of that whey when it is separated from cheese curd? Whey is primarily water, but contains some leftover proteins and sugars like lactose that aren't bound to fats in the cheesemaking process. Some cheeses, like ricotta and gjetost, are actually made from whey - traditions that developed back when people found ways to use up every possible bit of a product rather than throwing it out. As you might guess, it takes quite a bit of whey to make a little bit of cheese, because there is not much protein left.

Some small cheesemakers, like Juniper Grove Farm in Central Oregon, feed leftover whey to farm animals like pigs. Some states allow farmers to spread whey on fields, where it acts as a fertilizer. (Note: next time you make cheese at home, save the whey and use it as a fertilizer in your garden). But for those farmers and/or cheese operations that don't have animals to consume whey, or don't want to raise pigs, whey presents a whole host of disposal concerns. It's not as simple as just sending whey down the drain, because the sugars and proteins in whey make it a potent environmental pollutant. Check out this publication for more details about the potential hazards and toxicity associated with whey and whey disposal.

Whey protein is actually useful in the food industry, which is why some large cheese plants like the one at Tillamook have their own whey management systems. Specialized equipment dries and concentrates whey into a powder that can be sold to food processing plants, which use whey protein to make things like cookies, cakes or protein drinks. In Wisconsin, enterprising cheesemakers have recently banded together and developed a cooperative whey plant that will process participating cheesemakers' whey so it can then be purchased by companies that use whey in their products.

Another interesting use for whey: whey wine.

Molds & Presses

cheesemaking moldsOnce a cheesemaker is finished separating curds and whey and manipulating the curds in the proper manner required by a given recipe, she will usually place the curds in some type of form or mold.  Curds might be gently ladled into the mold (as they are when making soft ripened cheeses) or pressed in with great force and pressure (as with hard cheeses like Gouda) to remove their moisture. Fresh cheeses like fromage blanc or chévre are usually just packed into cheesecloth and drained over a sink or other receptacle, because shape is not a priority for a soft, spreadable cheese.

Molds serve a variety of functions including the obvious - determining the shape of the cheese - as well as providing a means of controlling the rate of drainage, which will affect the final texture and flavor. As with other aspects of the cheesemaking process, the size and shape of a cheese mold involves a complex set of choices related to what type of cheese you're making and how it needs to age, how much moisture the curd contains and how much you want it to retain over time, acidity...and so on. These choices have a huge effect on the final product  - you can make the best cheese from the best milk in the world, but if you make a bad choice here your cheese will not age properly and will not taste good. For a cheesemaker, the choices never end!

More about the aging process in the next installment.



Raw Milk Cheese Association

University of Guelph Cheesemaking site on the acidification and coagulation of milk using bacterial cultures and rennet. You can also look find their in depth treatment of pasteurization here.

Where do cheesemakers buy culture and rennet? Take a look at Fromagex or Dairy Connection

Next: How Cheese is Made Part III: Affinage, or, the Art and Science of Aging Cheese