The Science of Liver
THE SCIENCE OF LIVER
Science helps us to understand what liver is, and how to cook this offal to appreciate it the best. Don't miss the tips!
In the succulent and variegated world of offal, liver is the unquestioned protagonist. It owes this popularity to its particular composition. Anatomically speaking, liver is a gland, which serves multiple functions, the main ones being the storage of glycogen, protein synthesis and the production of bile. Hence its typical flavour, a delicate mix of sweet, bitter and acidic tastes which lend themselves to being enhanced in an endless number of recipes. Strictly speaking, it is possible to consume the liver of all those animals which normally provide us with nourishment, fish included, but the ones we are most familiar with come from pigs and calves since they are cheap, widely available and easy to cook.
THE CHEMICAL COMPOSITION OF LIVER
While differing from one species to another, the consistency of liver is always quite similar, this being something a skilled cook has to bear in mind. In particular, it is rich in glutathione and thiols. The former is a tripeptide made up of the amino acids cysteine, glycine and glutamate (which is the salt of glutamic acid) and is partly responsible for the “metallic” taste of liver. The latter are alcohols to which we owe the characteristic smell of this gland. During the cooking process, the two compounds have no small impact on the taste and aroma of this dish. To mitigate this somewhat aggressive flavour, it is a good idea to leave raw liver to marinate in an acidic substance, such as lemon or lime juice, or even vinegar. This will actually limit the oxidation of glutathione and thiols during the subsequent cooking process.
HOW TO COOK LIVER
There is no perfect way of cooking liver. To avoid errors and give your creativity free rein, you need to bear a few simple rules in mind. The first one has to do with consistency. Raw liver is gelatinous owing to the considerable amount of water it contains (about 70%) trapped by a dense network of proteins (20%) and fat molecules (4-5%). This means that it must be cooked rapidly at a high temperature. “Stewing” liver or subjecting it to a long slow cooking process leads to its dehydration, which makes the fibres tough and the resulting dish dry and difficult to chew. The more daring foodies like to eat very fresh calf’s liver served raw, cut into thin slices and dressed with oil and salt, but it is not necessary to go that far to enjoy this particular type of offal at its best.
Take Venetian-style liver for instance. In the eating houses of the celebrated lagoon city, the recipe differs from the one to be found in cookery books, and the basic rule is that the liver must be barely “seared”. Take half a kilo of pig’s liver (but nowadays calf’s liver is used to the same extent) and cut it up into strips. In the meantime fry two sliced white onions in 50 grams of butter over a very gentle heat. When half cooked, add three spoonfuls of white vinegar and one spoonful of water. Then increase the heat and add the liver, cooking it for no more than five minutes, before seasoning with salt and a generous dose of black pepper. Most important: the liver hasto be consumed immediately and never, never reheated. Rather than this, it would be better to eat it cold.
Piping hot, on the other hand, is the ideal temperature for Milanese-style liver, which is a sort of variation on the traditional breaded cutlet theme. The calf liver slices are used whole. They must be dried and then dipped first in beaten eggs and then in breadcrumbs, pressing the crumbs down to make them adhere well. Finally the liver slices are fried in plenty of groundnut oil but only for a few minutes, as in the previous recipe. Season with salt when cooked.
Time is precious also when preparing liver the Berliner way. First of all, peel four red apples and remove the core, before cutting them into slices about one centimetre thick and sprinkling them with lemon juice. Then take the slices of calf liver, add salt and pepper, dip them in flour and fry in a little butter for a couple of minutes on both sides. Heat some more butter in a saucepan and gently fry two large sliced onions to which you will also add the apples and, when these are cooked, a couple of spoonfuls of vinegar. The liver is then served with the onion and apple compote.
Leberwurst, on the other hand, is a type of sausage made from pig’s liver. It is not simple to make at home and it calls for very fresh cuts of meat. Practically, you take the pig’s offal comprising liver, bile ducts and gallbladder and blanch it in boiling salted water. When cold, it then hasto be minced with one third of its weight in raw liver, together with various spices and herbs. Finally the mixture is piped into a sausage casing and used fresh for spreading on bread. ---Try these recipes and you will realize what wonderful flavours a humble piece of liver can offer.