Which culture do I need?

Cheese cultures are an important part of the cheesemaking process and their importance should not be overlooked. Yes, you can use something to acidify the milk, such as lemon juice or vinegar but the resultant cheeses will likely be bland and lack flavour.  From a safety point of view, it is also best to use a starter culture. The use of vinegar, lemon juice, tartaric acid or citric acid should really only be reserved  for fresh cheeses that have a low finishing pH. 

When starting out it can be a bit confusing as to which culture is most suited to the type of cheese you are trying to make - but once you get your head around the basics it’s not too tricky!

How do they work? Lactic acid bacteria present in the culture (when added to warm milk), begin to convert the sugars present in the milk (lactose), turning them into lactic acid and in doing so, lowering the pH of the milk. At the correct temperature, these bacteria multiply and crowd out unwanted bacteria such as Listeria. Listeria being less tolerant of acidic conditions therefore cannot gain a foothold in the milk/finished cheese. As well as adding flavour to the finished cheese and helping to reduce the risk of harmful bacteria, lowering the pH of the milk also helps the rennet coagulate the milk, turning it into curds and whey. 

There are two main types of starter culture, Mesophilic and Thermophilic. Mesophilic cultures (Meso from the Greek word for medium) are used when you heat the milk to a ‘medium’ temperature. Most cheeses use a Mesophilic culture. Mesophiles which are the bacterial strains present in the culture, will grow from about 20°C up to 40°C. 

For harder cheeses such as Parmesan and Gruyère and also Mozzarella, typically a Thermophilic culture is used. The Thermophiles found in these types of culture won’t grow below 30°C and can withstand much higher temperatures than 40°C. Some cultures have a blend of both Mesophilic and Thermophilic strains. With these types of culture, the Mesophiles will grow at the lower temperature and do their part before dying off at the higher temperature when the thermophilic strains will then take over and start their work. 

Mesophilic cultures tend to come into two main types, Homofermentative and Heterofermentative. Homofermentative cultures will convert the lactose into lactic acid (as mentioned above). Heterofermentative cultures also produce lactic acid but as well as that add flavour compounds and produce some gas - small holes in the cheese. If you look at the bacterial strains found in a Homofermentative culture, you will see that they usually contain two strains, Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris. Think of these two strains as the acidifying bacteria. Looking at a Heterofermentative culture you will find that they usually also have these two bacterial strains but then often have other strains as well. An example would be Lactococcus lactis subsp. lactis biovar diacetylactis and Leuconostoc mesenteroides. Think of these two stains as flavour and gas producing compounds. When starting out, if you have a basic Thermophilic, a Homofermentative and Heterofermentative culture, you’ll be able to make a wide variety of cheeses. 

Cultures usually come in two forms, DVI starters and cultures where a starter solution is required. The latter involves using the culture to make up a starter solution, of which a small amount of this solution is used each batch to acidify/flavour the milk. DVI stands for direct vat inoculation - or direct saucepan, pot or whatever you are putting the milk into to make your cheese! As the name suggests you add  this culture directly to the warm milk. The cultures themselves can be in powdered or granular form and sometimes also liquid. They are best kept frozen once you have received them. As well as freeze dried cultures there are frozen cultures. These are a little different and have to be transported in dry ice, making them more suited for commercial users rather than small scale producers. 

The cultures will either tell you how much milk they will inoculate or they will have a unit of measurement. For Danisco cultures this would be DCU (Dansico Culture Unit). Christian Hansen cultures are measured in U (units). For example, a 200U Flora Danica culture will be enough to inoculate up to 2000 litres of milk. 1 U = 10 litres. 

For smaller scale users it is necessary to divide the culture up. Using accurate scales and a sterilised container with a lid, tip the contents into the container and record the weight. If the weight of the culture is 20g and one sachet of this culture is enough for 500 litres of milk and you wish to use 10 litres of milk then you can do the following equation.

20g ÷ 500 x 10 = 0.4g. You’ll therefore need 0.4g of culture for 10 litres of milk. 

Hopefully that has given you a better insight into starter cultures and how they work. In my next blog we will look at cultures that produce a secondary effect in the cheese such as the white mould found on the outside of a Camembert or the blue mould found in Stilton.