Cheese flavor and texture begins with choosing the right bacterial culture

To some extent you might think of cheesemaking as farming conducted at a microbial level. The character of a cheese is mostly derived from the nature of its microbial populations, so cheesemakers, like farmers, carefully nurture their desired crops of bacteria, yeasts, and molds. Bright orange washed-rind molds or striking blue veins easily get our attention, but most often it is actually the invisible population of lactic acid bacteria that shapes the flavor and texture of a cheese.

To understand how this happens, it’s essential to know that the first stage of almost all cheesemaking is the acidification of the milk. Starter cultures are simply strains of lactic-acid-producing bacteria that are added to the milk to ensure a prompt and controlled acidification. During the make these bacteria digest the lactose in the milk, creating lactic acid as a by-product. This is a kind of fermentation; it is one of the key variables that the cheesemaker observes to monitor the progress of curd.

However, the bacteria of the starter culture also have a significant role to play in the maturation of the cheese. During aging, the starter bacteria trapped in the formed curd die off and their cell walls break open, releasing enzymes that break down the fats and proteins within the cheese, thereby creating the flavorful and aromatic compounds that give a cheese its character. The breakdown of proteins by these enzymes also helps give soft cheeses their smooth, pliant texture. Similarly, in Swiss-type cheeses, the starter cultures will include strains of propionic bacteria, which in the later stages of cheesemaking consume some of the lactic acid (produced by their fellow bacteria) and release carbon dioxide gas, which slowly forms the holes (“eyes”) characteristic of many cheeses.

While cheesemaking is possible with no starter culture—simply by letting the indigenous lactic acid bacteria sour the milk—in practice almost all cheesemakers prefer the security of a more consistent and reliable acidification. Starter cultures can take many forms. At one end of the scale, the cheesemaker might retain some of the whey from the previous day’s make and use that to start the acidification. (This is a legal requirement for some cheeses, like Comté and Parmigiano-Reggiano, and a common technique used for many lactic goat’s cheeses from France.)

Alternately, dairy technology companies like Danisco sell freeze-dried, powdered starters for direct vat inoculation (DVI, also known as direct vat set or DVS). These are known strains in specific and consistent proportions that can just be sprinkled into the vat of milk. The websites of these companies offer a bewildering variety of different starters, each with their own flavor and acidity profiles. However, their very consistency and simplicity of use is also their greatest weakness; they are now ubiquitous.

In search of greater diversity of flavor, some cheesemakers in England who make British regional cheeses have taken to using old-world-style commercially cultured liquid “pint” starters. These are more demanding to use—they have to be bulked up in sterile milk—but they offer complex, undefined mixes of strains. The delicate liquid starters are kept frozen in liquid nitrogen, then grown at the creameries under precisely controlled conditions in reconstituted skim-milk powder. One English company, AJ & RG Barber Ltd., opened its laboratory in the 1990s to ensure the continued availability of the traditional pint starters when the big dairies began moving over to DVI. Chris Griggs of Barber Ltd. is proud of the link that these starters provide with the cheesemaking of previous generations: “The starters themselves must have been isolated from all over the West Country as cultures which happened to make good cheese. I would guess that the oldest are from the 1970s.”

It’s important to remember that all starter cultures were initially found in nature somewhere. Even the most industrially made sachet of freeze-dried DVI starter is simply something a laboratory has selectively grown from an original sample. Indeed, with starter cultures it is not so much what you use as how you use it. If the milk at a creamery is blandly sterile and receives a high dose of a single-strain starter, the resulting cheese will be monotone in flavor. However, the same starter culture used in a small dose to kick-start the acidification of good unpasteurized milk, rich in its own healthy microflora, will result in a cheese that expresses its own uniqueness, rather than the packet from whence its starters came.

Written by Francis Percival
Illustration by Jacqueline Rogers