Cheese is a great example of human diversity and ingenuity. From the desert to the Swiss alps, five simple ingredients—milk, bacteria, rennet, salt and time—have been turned into thousands of types of cheese. So how about a closer look at some of the steps involved in making cheese: the image above shows just a few of the more common varieties we eat.
The key ingredients to make a curd: acid and rennet
To turn milk from a liquid to a solid, we use acid and/or the addition of the enzyme rennet.
In most cases, the acid is produced by “starters”: lactic acid bacteria (LAB) that break down lactose and turn it into lactic acid. In addition to lactic acid, LAB and other cheese-making bacteria and moulds produce substances such as carbon dioxide, acetic and propionic acids, acetaldehyde, diacetyl and ethanol. These develop cheese texture, aroma, flavour, and colour during the aging process.
…but first, a close-up look at casein
To understand how lactic acid and rennet work, it’s important to look at the microstructure of milk protein: casein. There are four types of casein called α1, α2, β and κ. These are arranged in teeny-tiny, spherical networks called micelles, with the casein cemented together by nodes of calcium phosphate. As the diagram below shows, κ-casein with their negatively charged tails are arranged around the surface of the micelles. The negatively charged micelles repel each another, keeping them in suspension.
With the presence of lactic acid, the negative charge on the κ-casein is neutralised with the result that micelles can come close enough together to form a bond. Because calcium is lost from the micelles due to the drop in pH it does not aid in the bonding; the resulting curd is weak. A good example of this type of cheese is ricotta.
Rennet works by trimming off the negative tail of κ-casein and again, the casein micelles are no longer repelled by each other and bind together. Because calcium hasn’t left the micelles as the pH hasn’t dropped so low, it takes part in the bonding process and the resultant curd is stronger. The milk fat and whey (water, lactose and soluble whey proteins) are embedded in the casein curd. If LAB are present, they are also trapped and continue to produce acid within the curd. The picture below is from a great article that looks at cheese at a microscopic level: the white is the casein curd, the yellow blobs are fat globules and the light blue spots are bacteria.
Removing the whey…
Once the curd is formed it is cut, stirred, heated, drained, pressed and salted in a multitude of variations, depending on the type of cheese being made. These steps remove the excess whey. Generally the lower the water content, the longer the life of the cheese. The final cheese yield is proportional to the original fat and protein content of the milk.
Aging: where the magic really happens!
Whole businesses are dedicated to the art of aging cheese. Cheeses are wrapped, waxed, washed or left plain and stored for weeks to years, at various temperatures and humidity. During this time the casein and milk fat are broken down into their molecular building blocks: amino acids, ammonia, sulphur compounds, acids, alcohols, phenols, indols, amines, aldehydes, free fatty acids, ketones and carbon dioxide. These compounds create flavour and aroma and modify cheese texture. As you can see in the photos below, Camembert cheese undergoes quite a transformation!
#EatMoreCheese
One way to support our dairy industry is to eat more dairy products, and this includes eating more cheese! There are lots of ways to get more cheese into your day:
- Have a bagel with cream cheese or quark for breakfast
- Make Anzac yoyos for morning tea: mix cream cheese with a little golden syrup and sandwich two Anzac biscuits together
- Have Cheddar cheese and marmalade on toast for lunch (aka Cheese à la Marian)
- Make a salad of watermelon, feta and mint for an afternoon snack
Schooling @ home ideas
While home cheese making is fun to do, a lot of cheese types are hard to make unless you buy the starters, rennet and equipment. But ricotta is easy to make at home. This site has a step-by-step recipe for ricotta and also has recipes for ricotta-based sweet and savoury dishes.
Another cheesy idea is to stage your own cheese tasting! Buy 4 or 5 different cheeses and cut them into squares. Pick at least a couple that you haven’t tried before. One by one, write down what flavours you can taste and what textures you feel. Here are some examples to get you going: peppery, fruity, mushroomy, ammonia, garlicy, vegemite, salty, fishy, sweet, nutty, buttery, bitter, smoky, spicy, salty, acidic, cowy, grainy, smooth, creamy, rough, crumbly.
Happy tasting!
