Cheese in Depth: Equal Parts Art and Science

Pasteurization and Fermentation: the first steps in cheesemaking

Welcome to Part 2 of the “Cheese In Depth” series. In the first installment, we explored the variations between the three most common dairy breeds for cheesemaking: cows, sheep and goats.

Now we take it a step further, looking at the first stages in the cheesemaking process, from the handling of the milk through the creation of the curd. If this feels like a flashback to high school science class, it’s not surprising. Cheesemaking is equal parts art and science.

As we learned last month, cheesemakers use fresh milk as their medium for creating edible art. The optional first step in the process is pasteurization. Louis Pasteur, a French microbiologist, first tested the eponymous process in 1862, leading to breakthroughs in food safety and palatability.

The process involves heating and rapid cooling of milk during which natural bacteria and microflora in the milk, both beneficial and potentially harmful, are reduced significantly.

Unpasturized or raw milk cheeses are legal for sale in the US as long as they are aged 60 days or more. Some of the finest cheeses in the world like Parmigiano Reggiano, Gruyère and Roquefort are legally required to be made with raw milk.

Cheesemaking is a fermentation based process and has much in common with production of other fermented foods like wine, beer and bread. Fermented foods are produced or preserved by the action of microorganisms.

As in winemaking, where sugars are transformed into alcohol with the addition of a fermentation starter, namely yeast, in cheesemaking, the addition of starter cultures converts milk sugar, or lactose, into lactic acid, acidifying the milk. Because the lactose is converted to lactic acid, those who are lactose intolerant can enjoy all but fresh cheese which retains a trace of lactose.

Starter cultures also add flavor and may impact the texture of the finished cheese. Once the cultures are added to the warm milk, attaining the proper pH takes several hours as the bacteria multiply.

Many of the starter cultures are various species of the genus penicillium and are a distant cousin of the antibiotic penicillin. Penicillium candidum produces the characteristic white rind on brie and camembert. Penicillium roquefortii causes the distinctive blue veining in Roquefort and other blue cheeses.

Many people notice similarities in flavor between the white rinded and blue molded cheeses and even note subtle medicinal flavors. Not surprising due to their close relation in the world of molds and medicine.

When the milk is sufficiently acidified, the cheesemaker adds a small amount of rennet, an acid of plant, animal or microbial origin. Traditional rennet was derived from the stomach acid of young cows, sheep or goats. Some plants such as thistle will also coagulate milk.

Rennet contains the enzyme rennin which, in the span of about 30 minutes, severs the protein structure of the milk, causing them to coagulate or clump and bind together. During coagulation, milk is transformed from a liquid to a semi-solid state, similar to soft-set gelatin. Coagulation produces solid curds (protein) and whey, a liquid that is mostly water with some residual proteins.

These preliminary stages of cheesemaking – from the addition of the starter cultures and rennet, through the transition from liquid milk to a solid mass – are the same regardless of what type or style of cheese is being made.

From here, how the cheesemaker handles the coagulated milk and how it is aged will determine what sort of cheese is being made and impact its appearance, aroma, texture and flavor. This will be the subject of Part 3 - From Curd to Edible Art.