Starter Cultures, Coloring Agents, and Spores
Left alone, raw milk will spoil and become cheese-like, but the results are uneven and unpredictable. Because pasteurization kills most bacteria, pasteurized milk will not spoil in a way that produces cheese. As a result, starter cultures are used to introduce helpful bacteria that spoil milk in a controlled way before it is separated into curds and whey.
One of the first steps in converting milk to cheese is taking advantage of lactose. As milk ages, the lactose it contains turns into lactic acid, which in turn allows desirable and undesirable bacteria to develop. By using starter cultures to promote the development of lactic acid in fresh milk, cheese makers are able to control against harmful bacteria and promote the growth of beneficial microorganisms.
Two families of starter cultures are used to make cheese, mesophilic cultures and thermophilic cultures, both available in freeze-dried form from dairy-supply companies. Mesophilic cultures thrive at room temperature while thermophilic cultures require higher temperatures.
Not all starter cultures come freeze dried. Long before freeze-drying was available, cheese makers carefully preserved milk from one day to be used as starter cultures for the next day. This method is still used and is called using a mother culture.
Mespophilic cultures work best in moderate temperatures (50°–108°F), and are used when making fresh, bloomy-rind, soft, semisoft, and washed-rind cheeses. Thermophilic cultures survive at higher temperatures (68°– 125°F), and are used when making semihard, hard, and cooked-curd cheeses, such as mozzarella, Gouda, and Swiss. Some cheeses are made with a combination of mesophilic and thermophilic cultures. For example, Swiss cheese varieties use both cultures. They use thermophilic cultures to produce the right texture, but they also take advantage of a specific mesophilic culture that contains carbon dioxide. During aging, the carbon dioxide gas creates eyes, or holes, in the cheese.
Natural cheese color ranges from creamy white to buff and reflects the type of milk used. Goat's milk produces the whitest cheese, cow's-milk cheese is naturally cream to butter colored, and sheep's-milk cheese tends to have yellow, buttery tones. Even with this range, cheese makers have found it fun and interesting to experiment with different colors of curd.
One of the most successful and widely used food dyes is an extract of the seeds of the annatto tree, Bixa orellana. Grown in the tropics, the seed is commonly used for coloring dishes such as Spanish rice. You'll find annatto listed as an ingredient in cheeses that have been made for hundreds of years, like Mimolette, and in newer cheese products like Velveeta.
The beautiful French cheese Mimolette is one of the most famous cheeses colored by annatto. The cheese is aged in balls about eight inches wide and high, and coated with salt. After eighteen months of turning and aging, the salt and the curd develop into a natural buff-colored rind, forming a hard ball that looks almost impenetrable. However, when sliced open, a bright orange paste is revealed, making the entire cheese appear to be a brilliantly colored cantaloupe.
Natural colorings are also added to the rind of cheeses. For example, Drunken Goat, a semisoft cheese from Spain, is rubbed with red wine while aging. The result is a gorgeous purple rind set against a white goat's-milk cheese. It's a wonderful treat on a hot summer day. In the United States, the FDA allows the milk of some cheeses to be bleached and the curd to be colored by specifically approved natural and artificial food dyes.
When starter cultures are introduced, mold spores can also be added to produce rinds and molds. This technique is often referred to as seeding the starter culture. The two most common types of mold spores added to cheese are Penicillium candidum and Penicillium roqueforti.
Bloomy-rind cheeses have white, green, floral, and/or grey rinds that look a bit like velvet. Some cheeses like Bries and Camemberts have pure white rinds, while others, like Selles-sur-Cher and Valencay have bloomy rinds grown over layers of vegetable ash. Either way, the bloomy rind is the result of a mold spore called Penicillium candidum. In France, Penicillium candidum occurs naturally in aging caves, and these spores are harvested and reproduced for cheese makers around the world. The spores arrive in freeze-dried form and are added directly to the milk along with starter cultures, coloring agents, or both. Nothing happens to the curd right away, but while the cheese is aging it literally blooms with a soft, velvety white mold.
Not all blue cheese is called Roquefort. The name “Roquefort” is controlled by the
In France, some bloomy-rind cheeses are not inoculated with Penicillium candidum during the starter-culture phase. Instead, the cheeses are aged in rooms or caves that have been used for this purpose for decades, some for hundreds of years. Only one kind of cheese is aged in each cave or room, as the mold is part of the room and forms on the cheese without being introduced in any other way. To some, the results are indistinguishable from cheeses inoculated during the starter-culture phase.
The mold you see in blue cheese is grown by Penicillium roqueforti spores, which come in many varieties. Almost all blue cheeses are made with a strain of this spore. Again, these spores occur naturally in the caves of Roquefort, France, and are harvested, reproduced, and distributed worldwide in freeze-dried form. Penicillium roqueforti works differently than Penicillium candidum. Instead of growing a bloomy white rind on the outside of the cheese, it grows a bluish green mold inside the cheese.