Wednesday 6 January 2010
When I think of cheese, my mind returns to a mountain farm in the French Pyrenees with a spectacular view across a green valley to the snow-covered peaks that mark the border with Spain. From the farm’s small flock of dark-eyed Jersey cows, colourful goats and ignorant sheep came the most incredible cheeses.
I spent a month working on this farm. I took goats for walks with Iglo the farm’s shaggy dog of disorder, milked cows with rough tongues that would scour your face if you were looking the wrong way, and made cheeses: soft goat’s cheeses, gentle whey cheeses and beautifully round matured ewe’s milk Tomme. It was amazing to feel the warm fresh milk in my hands as it transformed from gentle liquid to soft, solid curds and then, with time, witness the development of such an array of flavours and textures.
The transformation of milk into cheese is one of the most extraordinary of all human discoveries.
No one knows exactly when, 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.
On that little farm where I worked in the Pyrenees, the sheep were milked by hand, the cows and goats by a combination of hand and machine. To taste this milk was to taste the flavour of the land on which the animals lived. This flavour imparted itself to the cheese, making it truly regional.
After the early morning milking the cheesemaking would begin. Our dirty farmyard clothes were exchanged for white coats and boots, our hair (and my beard) trapped behind hairnets. This was when the fun began, the mixture of cooking, chemistry and adventure that is cheesemaking. The basic stages are not complex but the variables are endless, which allows for the enormous variety of cheeses that can be found around the world.
Ripening or souring the milk
All of the cheese produced on the farm was made from unpasteurised milk. This meant that the first step happened all by itself. Bacteria naturally present in the milk would start souring it, converting lactose (milk sugar) into lactic acid. In cheese made from pasteurised milk these acidifying bacteria must be added.
Although pasteurised milk will acidify if left in the fridge too long, the bacteria that grow are unknown bacteria, possibly dangerous, certainly smelly. The types of bacteria added to acidify milk in cheesemaking are carefully controlled.
Pasteurisation was introduced, in part, due to urbanisation and the separation of people from the farms where milk was produced. Sources of milk became less reliable and illnesses such as tuberculosis were rife. Pasteurisation was a lifesaver. However, many cheesemakers (especially in France) argue that it is also a flavour-killing process because the bacteria, which persist into the drained curd, generate much of the flavour during ripening. But that is an argument for another time.
Curdling and coagulation
Getting up early in the morning to be faced with a giant cauldron of smooth, creamy, slightly soured milk from 60 ewes is an intimidating experience. But it was here that the cheesemaking really started. We needed Little Miss Muffet’s curds and whey and we got them by separating or “curdling” the milk using enzymes found in rennet. Curdling occurs when certain milk proteins clump together forming a web or matrix that traps water and fat.
The use of rennet may have been humankind’s first venture into biotechnology. Rennet was probably discovered when curd was observed in the stomachs of young animals during butchery, or possibly when the stomachs of certain animals were used as handy bags for carrying milk around.
Cheesemaking was either carried out in a calf’s stomach or with a piece of stomach in a vessel. In time cheesemakers learned to extract the enzymes using brine and now we can produce vegetarian rennet in a laboratory.
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.
On the farm we saw little of this fascinating science as, after adding the rennet, we went off to drink a morning coffee and eat hunks of fresh bread with honey for breakfast, leaving the rennet to do its work.
Cutting and cooking
On our return, the slight buzz of strong coffee still in our veins, the first of many magical transformations had occurred. The pristine liquid milk had solidified into a rubbery, ivory gel. Now I had to “cut”, or separate, the curds and whey by diving my (very clean) hands into the soft matter. I would grab handfuls of thick, custard-like curds and feel them break into tiny pieces in my hands, the warm, wet whey squirting out through my fingers.
Breaking up the curd helped remove the whey, giving a firmer cheese: the more was removed, the firmer the cheese. To make the farm’s special Tomme cheese the curds were gently cooked in their whey, giving a slight rubbery texture. The very rubbery texture of cheeses like Gruyère comes from more intensive cooking.
The small gas stove was lit under the giant cauldron and the curds and whey were warmed. They were stirred by hand and as the mixture heated I could feel the curds become rubbery between my fingers as more whey was driven from the network of protein molecules.
Salt can be added at this point to provide not only taste but also to inhibit the growth of spoilage microbes and draw out yet more water. Along with salt, mould spores can be added in various ways depending on the type of cheese to be produced. For Roquefort, the Penicillium roqueforti fungi were traditionally added in the form of ground bread left to go mouldy in the famous Roquefort Caves in the south of France.
Moulding and pressing the curds
Moving your hand though warm curds and whey is a strange experience. I was acutely aware that they must not overheat, but also distracted by the mixtures of textures and sensations within the cauldron. After letting it cool I would plunge my hands back into the mixture, forming the firm grainy curds into a giant white wobbly ball which – fearful of dropping – I had to quickly transfer to the cheese cloth in the colander-like mould. Here, the whey drained away though the cheese cloth with the help of a little pressure from another moulded cheese.
This process of moulding the cheese is critical: the shape of the mould, the application of pressure and the proportion of whey removed all have major effects on the final cheese, especially on its texture.
If you want a really dry, hard cheese (for example cheddar) you must “mill” or “cheddar” the curds. This means breaking the curds into very small pieces, which reduces the moisture content still further. More salt may then be added and the cheese squeezed in a giant press to remove yet more whey. Such pressed curds end up as very dry cheeses such as Cheshire.
For softer cheeses more of the whey is left with the curds. They have a moist, open, airy texture and hence provide great conditions for the growth of moulds that require air for growth. This can be an advantage for mould-ripened cheeses such as the beautifully blue-veined Stilton, but can also mean they spoil more rapidly.
Maturing or ripening
This is the final and slowest transformation. Here we can see how milk and cheese live on a knife edge between life and decay. If the milk is not pasteurised then there is life and growth at every stage, from animal to milk to cheese. But in the end it is a form of decay that gives cheese its flavours and textures. As cheeses age and decay they develop flavour and character, mould and even personalities.
However, given too much time a cheese can become harsh and coarse.
The lives of soft cheeses like Brie and Camembert are meteoric: their prime comes and goes within weeks. The white surface mould that characterises them produces an enzyme that penetrates the cheese, breaking down the casein protein network and transforming the chalky curd into the runny, smelly substance that we enjoy. Left too long, however, and the protein structure collapses into an unpalatable, stinky mess.
For harder cheeses the ageing process is prolonged for a few months to a year, or even, for really dry cheeses like Parmesan, several years. With more time, the decay of the casein proteins allows more flavour-producing chemicals to form.
First, the proteins break into medium-sized pieces called peptides and then into smaller amino acids. These can in turn be broken down into various, highly flavoured molecules called amines. At each stage more complex flavours are produced. For example amines can have smells ranging from spoiling meat to sulphur-like smells, or even ammonia. Though these scarcely sound appetising, bare hints of them build the complexity and richness of cheeses’ flavours and smells.
Alongside the breaking down of proteins, fats can also be degraded, particularly by blue-cheese moulds such as P. roqueforti. These fats become fatty acids, which in turn become smaller molecules with many of the characteristic smells and flavours of blue cheeses. Some fatty acids have a peppery effect on the tongue and an intense sheep or goat aroma.
The more diverse the cast of ripening enzymes, the more complex the resulting collection of protein and fat fragments and the richer the flavour. A flavour that is still of the land but has developed a life of its own.
Back on the mountainside in the French Pyrenees we would remove the cheese from the mould and transfer it to a cave kept at the correct humidity and temperature by the mountain air and a giant waterfall near its mouth. The cave smelled damp but clean. There was an earthy smell but also a background aroma of cheese that grew the longer you stood there, into an overwhelming, mouth-watering, nose-filling sensation. The walls, the shelves, the cheeses, everything was alive with enzymes, bacteria and moulds all working together to produce the incredibly complex flavours in cheese.
We would retire from work for the day to watch the sun set over the mountains with a glass of warm, fruity red wine and a slab of perfectly mature cheese on a piece of crisp French bread. All around would be the smell of spring, the sound of the cow bells as the animals came in for the night, and the gentle background rumble of the waterfalls that raced though the farm and gave it its name, La Ferme des Cascades.
Image by Susy Morris (http://tinyurl.com/pe8dhna)