Exploring chemical reaction when making cheese with Norton's Dairy

What another lovely day spent at Nortons Dairy. The key to great cheese is the quality of the milk, which is where Nortons Dairy comes into its own with its own closed herd of cows. Their cheese as a result has a fuller, richer flavour.

No one knows exactly when cheese was first made, but it is believed to have happened at about the same time as the domestication of animals such as goats in the fertile crescent region of the Middle East around 6,000-7,000BC. A forgetful shepherd might have noticed that his neglected milk turned acidic and curdled into a thick yoghurt. This yoghurt could then be separated into solid curd and liquid whey. The whey provided a refreshing drink on hot journeys. The fresh curd could be salted to produce a simple cheese, maybe the first ever cheese.

Today I learnt that to make cheese you need an instant-read thermometer, some citric acid, to help acidify the milk; and some rennet to separate the curds from the whey. The active enzyme in rennet is special because it only acts on one type of milk protein: casein proteins. These occur in milk as clumps known as micelles, held together by a calcium "glue". The micelles have negative charges over their surface which makes them repel each other and so they stay separated in the milk. To form curds, either rennet or an acid is used to overcome these negative charges and create a network of casein proteins.

If an acid is used (for example vinegar, lemon juice or bacterially produced lactic acid) the micelles are broken up, the negative charges removed, and some of the calcium "glue" is lost into the whey. This allows the casein proteins to join together but in a weak network, forming brittle curds that are deficient in calcium.

Acid-curdled cheeses, such as cottage cheese, are usually eaten fresh, with the whey drained off and some salt added. They tend to have little flavour because many flavour-producing enzymes do not work well in these acidic conditions.

By contrast, rennet removes the negative charge on the micelles but does not break them up, allowing them to join together in a much stronger network and form more elastic curds. Cheese made from these curds can be matured for long periods of time, developing complex flavours. At Nortons Dairy they produce four flavours of cheese. Here you can see the Ladies busy packing their lavendar soft cheese.