Craft and science: the cheesemakers

Guests at Irish embassies on St Patrick's Day didn't only pass around the shamrock, there was something else on the menu. They were invited to tuck into a range of Irish cheeses, Durrus, Coolea, Cashel Blue and Knockanore smoked cheddar.

For them it was all about the taste, but in reality achieving the complex cheese flavours not only showcased Irish food, it showed how cheesemaking is a blend of tradition, craft and science.

A seemingly minor difference in milk can have a big impact on cheese, says Dr Michael Tunick, a US chemist whose book The Science of Cheese comes out next month. "Anything the cow eats gets carried over," he says. "Hundreds of flavour compounds have been identified in cheese."

That Irish cows feed on pasture matters. Conditions during processing are even more important – they determine which microbes thrive.

Dubbed the "wine of food", cheese is fermented by microorganisms deliberately added after milk gels due to rennet, an enzyme originally obtained from calves' stomachs. Whey is drained off and the curds are treated to encourage or discourage the growth of bacteria, fungi and yeast, giving us the 2,000 cheese varieties.

"It is probably one of the most complex industrial fermentations because you cannot make cheese from sterilised milk," says Prof Paul McSweeney, cheese scientist at University College Cork. "In most industrial processes you kill off the microbes by sterilising. You can't do that for cheese and that makes the microbiology more interesting."

Cheese dates back to at least the sixth millennium BC and was a way of preserving the nutritious value of milk. But cheese is also incredibly dynamic involving thousands of microorganisms and hundreds of flavour compounds, which develop with age. Understanding microbiology helps with consistency.

More than 1,400 scientific papers mention cheddar in their title, yet it is still impossible to guarantee how a batch will taste or know if it will develop into tangy mature cheddar. Understanding the microbiology helps with consistency though.

Blues and cheddar
Sheridan's Cheesemongers supplied the four farmhouse cheeses as their cheeses of the month. The presence of microorganisms is obvious in blue cheeses such as Stilton.

While tasting Cashel blue in Sheridan's in Dublin, manager John Leverrier says they let the wheels mature for 14 weeks. Dormant spores of the blue mould grow when the cheese is skewered and oxygen enters; the mould, Penicillium roqueforti , traditionally came from stale rye bread and was sprinkled onto Roquefort cheese.

Roquefort is distinctively French, but no native cheese survived our turbulent history. “Old Irish literature mentioned names of certain cheese and whether they were hard or soft, but no details of how they were made,” McSweeney explains.

Cheddar is an internally bacterially ripened cheese, meaning microbes don’t grow on its outside; instead it ripens inside, as enzymes break down fats and proteins, releasing flavour compounds. “What we think of as cheddar is the combined effect of a large number of compounds. Some are more important than others, such as sulphur-containing compounds like methanethiol,” says McSweeney.

After acid has developed, cheddar cheese curd is cut into small pieces, salt added and the curd pressed. “You wouldn’t recognise freshly-made cheddar,” says McSweeney. “It takes time for the flavour to develop and strong flavoured cheddar is older, though you can’t set out to make mature cheddar because there is still a bit of serendipity in how the cheese ripens.” Adding salt helps determine which bugs survive in a cheese.

Ireland’s late return to cheese manufacture had an upside; a wealth of knowledge was tapped to create our own varieties of European-style cheeses. Farmhouse cheese production is relatively small in Ireland, says McSweeney, but it has had a big impact on our cheese culture.

One example is Durrus, a semi-soft cheese with a mottled orangey rind, creamy texture and earthy flavours. This is a rind-washed cheese, a sort first created in European monasteries perhaps 1,000 years ago (see panel). The colouring is produced by bacteria and yeast, encouraged by wiping the outside with a damp cloth and storing it in high humidity. Durrus is eaten within weeks.

Coolea, on the other hand, is a gouda-style cheese made near Macroom that can be aged two years to give a milky sweetness. “Gouda is a long-lasting cheese. It was made to trade with and the Dutch would have traded it long distance,” explains Sheridan’s owner Kevin Sheridan. Gouda can age for a hundred years, becoming dry and flinty.

Sheridan's also stocks Irish buffalo mozzarella, made using a herd of more than 200 Italian water buffalo grazing in Toonsbridge in Cork. "Cheese is such a fantastic mix of science and artistry, " says Sheridan. "Making artisanal cheese involves science and instruments but also feel, touch and taste to make decisions."

Limburger: the 'dirty sock' cheese
Limburger is a northern European cheese which smells of dirty socks. Such cheeses are smear ripened; their outside is wiped with bacteria such as Brevibacterium linens. There is a scientific explanation for the odours. The surface of human and animal skin is the more natural habitat of the bacteria that is applied to the Limburger.

You might be put off by the foot odours or yuk factor of B linens, but scientists say it produces compounds that kill food poisoning bacteria as well as some moulds and yeasts. This kind of cheese originated over 1,000 years ago in monasteries.

“A lot of cheeses were made by happy accident,” explains cheese expert Michael Tunick of the US Department of Agriculture. “Where you leave milk lying around or a piece of cheese sitting in a vat, naturally occurring bacteria or mould comes and settles on it.”

Smelly Limburger actually has quite a mild flavour side. The pungent aroma is caused by extensive breakdown of fats which generates lots of short-chain fatty acids. Butyric, caprylic and capric acids give the rancid, sweaty aromas; these are prime contributors to foot odour too.

The Irish cheese Gubbeen has a pinkish rind with a white bloom – this crust is a triple-layered bloom of different organisms. The first is yeasts, next B. linens. The rind is finally topped with a bloom of white mould. Gubbeen is described as having a nose of mushrooms, nuts, bogs and forest floor.