What is a Starter Culture?

Starter cultures are generally bacterial, and they are added to the milk at specific temperatures to ripen it. What they actually do is slowly (the slower the better, in fact, as more desirable flavours and structures are generated) acidify the milk by converting the lactose sugar present into lactic acid. Before the modern era of cheese making, these bacteria would have been one of a number of natural microbes contaminating milk. Over time cultures or strains have developed from the practice of using the whey from a successful batch of cheese making as the starter culture for the next batch. Today very finely controlled cultures are grown in labs around the world for quite specific outcomes, such as buttery taste, holes in cheese, texture, etc.

There are two groups of starter culture: mesophilic and thermophilic. Mesophilic bacteria like moderate temperatures, so you’ll find recipes for cheeses using them call for milk to be at a temperature of around 30C (86F), which is the temperature they are most proficient at converting lactose to lactic acid. Thermophilic bacteria, as the name suggests, prefer warmer conditions, and you’ll see recipes using them need milk temperatures of around 42C (108F).

All together there are 16 broad types of bacterial starter which can be purchased from cheese making suppliers as either pure strains such as meso I which has just one bacterium type within it and is suitable for making cheddars, to Aroma B which has a blend of four bacteria and is used to make Camembert, amongst others.

Buying cultures for making cheese at home is a straight forward process. There are a number of suppliers which can be found through a search engine selling pre-blended and packaged cultures. They generally stay away from technical names and instead have the more helpful convention of saying ‘culture for goats cheese’ or ‘starter culture for Parmesan’ which makes it easy to know which to order. The better suppliers will als tell you about any additional cultures needed or conditions which must be maintained for the starter to work well.

One frustration that you are likely to experience comes from the small quantities of milk we deal with when making an individual cheese at home. Generally, a sachet of starter culture will be enough to treat anything up to 50 or 100litres and it will only contain a teaspoon or two of starter powder, of which you’ll need just a fraction. A great tip for really accurate measuring is to invest a small amount in some (very) small measuring spoons which go down to an eighth or quarter of a teaspoon, that way you’ll be ensure the right amount of culture for the qunatity of milk you are using.

On the positive side of the quantity issue is that cultures can be stored for up to two years in the freezer (although you should always pay attention to the instructions from your supplier) but keep in mind the golden rule: your bacterial starter must always be kept dry! Even the smallest amount of moisture getting into the packet will spoil the whole amount.

It is possible to create a mother culture of your own, which can then be used to create your own starter cultures (very similar to the process of using a sourdough starter in bread making), but that is an article for another day.

So, for virtually all cheeses, if you have the right milk, rennet and an appropriate starter culture you’ll have almost all you need to get going. However, there are one or two additions that might be relevant, depending on the type of cheese you’re making and the milk being used, and we explore those additional cheese making ingredients in the next beginner’s article.