by Tom Stobart
Oka, occa or oca (Oxalis tuberosa) is a native of the South American Andes – Ecuador, Bolivia and Peru. It is an important food tuber in South America with the typical shamrock-shaped leaf of the genus and whitish or brownish tubers. It grows quite well in the European climate and is said to have gone wild in parts of France. The tubers are acid when fresh, and in the Andes they are dried for several days in the sun before use to dissipate the acid. Although oka was introduced into England in 1829, it has never become popular. Larousse Gastronomique suggests parboiling and sautéing it in butter. Leaves and shoots can also be eaten in moderation, but like any Oxalis should be watched for oxalic acid.
Ysaño or añu is a South American tuber (Tropaeolum tuberosum) closely related to the nasturtium (T majus). A perennial climber, it is widely grown as a decorative flower, but there are mixed opinions about the culinary value of its knobbly yellow tubers. In Bolivia, they are claimed to be a delicacy if they are frozen after boiling, but another view is that they are just nasty.
Ulluco (UIlucus tuberosus) is another tuber from western South America. The plant is a half-hardy perennial which may be attractive to people who like uncommon vegetables. It has been grown in Britain. The small pink or yellow tubers are planted in the spring and lifted in the autumn after frost has killed the foliage.
Patra (India)
Pour boiling water over 100 g (4 oz) tamarind, leave it to cool and sieve the pulp from the seeds and fibre. Mix the pulp with 50 g (2 oz) gur (brown sugar), 150 g (5 oz) *besan flour, 1 teaspoon powdered turmeric, 1 teaspoon powdered coriander, 2 teaspoons powdered chilli (to taste), and 1 teaspoon *garam masala. Add water to make a thick mixture of spreading consistency, and salt to taste. Cut out any thick stem and veins from 12 taro leaves (arvi), but otherwise keep them whole. Lay the first leaf glossy side down and spread a layer of the paste on the rough side. Put another leaf shiny side down on top and spread it. When you have a stack 6 leaves thick, interspersed with the besan spread, roll it up like a Swiss roll and secure it with thread. Repeat with the remaining 6 leaves. Steam the rolls for 35-45 minutes (pierce them to see if they are tender), then remove the rolls, cover them with a cloth and allow them to cool, but while they are still warm, cut them in slices 1 cm (½ in) thick. Deep fry the slices to a red-brown colour and serve them garnished with 2 tablespoons chopped green coriander leaves, 2 tablespoons grated coconut and wedges of lime or lemon. This is a well-known dish in Bombay – spicy, sweet-sour and unusual.
Curried Yam (Suram)
Peel the 1 kg (2 lb) elephant’s foot yam, cut it into cubes and leave it to soak in salted water for 2 hours. Drain, dry and fry it. In a separate pan, fry together 1 teaspoon each of coriander, cumin and chilli gently until they are brown (but not burned). Add the yam, give it a turn and cool it with a dash of water. Add 25 g (1 oz) tamarind pulp or yoghurt when the yam is almost cooked. Sprinkle with chopped green coriander leaves before serving. Yam cubes may also be steamed, lightly browned in oil, then mixed with yoghurt, chopped green chillies and coriander leaves, seasoned with salt and a pinch of ground cumin seed, and served as a raita with curry.
[Yam – French: igname German: Famwurzel Italian: igname Spanish: ñame]
YAM BEAN. See yam.
YARD-LONG BEAN. See cowpea.
YAUTIA. See yam (yautia).
YEAST. Men used yeast for thousands of years without knowing it was composed of a mass of living organisms. Yeasts are single-celled, microscopic fungi. They commonly multiply by budding off daughters – a few kinds simply split in two like bacteria – but they also go in for sexual acts occasionally, so can form hybrids. To resist adversity (such as drying or too much alcohol), they can form *spores, for survival (not for multiplication). The atmosphere always has yeasts floating in it, and they are also introduced into the kitchen on fruit and vegetables. They drop into anything that is left uncovered.
Different species of yeast (and different strains within the same species) have individual characteristics. From a kitchen viewpoint, we can classify yeasts as wine yeasts, brewer’s yeast, baker’s yeast, wild yeasts and others. For rapid multiplication, yeasts need a good supply of air, but fermentation rather than growth is encouraged by the absence of air. Air is usually excluded during fermentation (and is often excluded naturally by the carbon dioxide that is produced), because air would encourage the bacteria that turn alcohol into acetic acid. lt is worth noting that as fermentation is caused by enzymes made by the yeasts, the process can go on even when the yeasts are dead, though treatment that kills yeast is likely also to destroy the enzymes. More heat than you can stand with your hand (the temperature for making 50°C or about 120°F) will quickly kill yeasts, even the spores, but they can stand being frozen, which is why yeast and bread dough can be kept for some time in the freezer. On the other hand, they need warmth to multiply – 25°C (77°F) is about right – and they prefer an acid medium of from pH 3.0-6.0; pH 5.3 is right for beer-making. Yeasts vary in their tolerance to alcohol (which they make themselves). It is no chance that man prizes yeasts that will thrive in a goodly amount of alcohol and calls the rest-the species which cannot hold their liquor- wild yeasts. Yeasts are inhibited by carbon dioxide gas under high pressure, a fact that is useful in the bulk storage of fruit juice in an unfermented state before filtration and bottling.
Bakers’ yeast (Saccharomyces cerevisiae) can be bought fresh, as a compressed tan, clay-like substance, or as dried active yeast granules. Fresh yeast is not a pure culture, but contains fully active vegetative cells which will start to multiply immediately when mixed with warm sugary water at about 37°C (100°F). It will store well in the refrigerator for 10-14 days. If frozen, it should be used quickly after it has defrosted: it is most practical to package it for the freezer in 15-30 g (½-1 oz) lumps. For bread, 20 g (¾ oz) of yeast per 1 kg (2¼ lb) of flour is sufficient, although for fast, light results, more can be used. However, according to Elizabeth David, the more yeast that is used, the quicker the bread will dry and the less flavour it will have.
Active dry yeast has a considerable shelf life even at ordinary room temperature, but, being in an inactive state, takes a little longer to get going. This yeast should be softened in warm water or milk at about 43°C (110°F), but if it proves stubborn about behaving as its packet says it should, add a little sugar, glucose or honey and a squeeze of lemon to the liquid. For baking, fresh yeast is replaced by half of its weight of dried yeast.
Yeast cultures can be kept alive indefinitely by feeding them with sugar and starting up new bottles weekly with a bit of the old culture, as was once generally done and still is in out-of-the-way places. Such are the ‘hops’ used by Australian drovers, and these yeast stocks usually produce *sourdough bread.
For some reason, many people fight shy of using yeast, but it is easy to handle. The usual reason for failure is getting the dough too hot and so killing the yeast, or keeping it too cold, in which case the yeast hardly has a chance to function. Keep the dough nicely warm, like a baby, and the yeast should work. One touch of perversity is that yeast, like people, may become sluggish in very hot weather. If bread is heavier than usual during a heat-wave, add marginally more yeast than the recipe demands. And to test whether a yeast dough has finished its first rising, make a dent in the top of the dough with a finger tip. If the dent puffs back up, it should be left to rise further, until it does not spring back to the touch. Then it is ready to be punched down.
Brewers’ yeast. There are two categories of brewers’ yeast. One works mainly on the surface of the vat and is used for making most types of British beer, the other works more slowly and coolly on the bottom of the vat and is used to make lager and American beer. Serious home brewers must try to get the right type of yeast for the type of beer they wish to brew. Certainly never use ordinary bakers’ yeast if you can help it, as the flavour will be very inferior (although some dried yeast packages give instructions for doing so.)
Wine yeast (Saccharomyces ellipsoideus). Until fairly recen
tly, winemakers relied on the yeasts that occurred naturally on their vines; strains of yeast were associated with different types of wine. Today with more scientific control there is a tendency to introduce pure cultures of the strains required. Wine yeasts influence the taste of the wine (although a champagne yeast used on sugar and water will not make champagne). Ever since wine-making became legal in Britain, it has been possible to buy suitable strains of yeast for various styles of wine from shops catering for home wine enthusiasts. This has resulted in great improvement in flavour- you can even buy sherry yeasts which give the correct skin or flor on the surface of the vat. It is also possible now to increase the alcoholic strength of the drink, as one of the important differences between wine yeasts and other types is their ability to tolerate alcohol. Under special laboratory conditions, they have produced a concentration of up to 20%, but 10-14% is more normal. Wine yeasts come in powdered, granulated or tablet form, as well as in liquid yeast cultures.
Wild yeast (Saccharomyces spiculatus) and yeasts of the genera Torula and Pichia. The wild yeasts are a nuisance to winemakers as they create bad flavours. They are usually quick off the mark, but luckily are quite sensitive to alcohol and are inhibited when the concentration reaches about 4%.They are much more sensitive to sulphur dioxide (see preservatives), than wine yeasts, so even though the number of wild yeast cells on one grape is often around 10,000,000, as compared with 100,000 of the wine yeasts, they are easy to control – 100 parts of sulphur dioxide per million is adequate. But this treatment of wine is frowned upon – there are legal limits to sulphur content in most countries. France allows up to 450 parts per million, but as little as 300 parts per million can be detected by taste in white wine. Another method of controlling wild yeasts is with alcohol. If the alcohol content of the must is brought up above the 4% mark by adding wine, then the wild yeasts will stop growing. Among other wild yeasts, some of the Pichia species are commonly seen growing on the surface of pickles, where they form a white skin or flor (as sherry yeasts form a flor on sherry). Though it is harmless, such a skin should be removed, because after a time it will create flavours in the pickles.
Yeasts in milk. There are usually yeasts in milk and they are sometimes responsible for creating unpleasant yeasty tastes in cottage cheese and yoghurt. They play a minor role in the microbiology of certain cheeses and are involved in the making of some sour milk products. An example is a yeast called Saccharomyces taete, which is necessary in making Swedish rangmjölk or täte, a sour milk product containing up to 0.5% alcohol. The correct souring of the milk depends on a bacterium called Streptococcus lactis which works in conjunction with the yeast, for the yeast will ferment milk sugar to alcohol only in the presence of lactic acid bacteria. Such symbiotic behaviour makes it far from simple to understand what goes on in foods made by the action of micro-organisms.
Health food yeasts. During World War II, many inmates of prison camps managed to stay alive by growing yeast, which is rich in protein, phosphorus, potassium and some of the B vitamins. Health food yeast is usually dried and dead (which it should be). It may be brewers’ yeast or Torula yeast, which is even higher in nutrient value and more tolerable. Some yeasts are debittered to make them more palatable. It is usually recommended, that yeast be taken in orange juice in the hope that this will mask the taste, but I prefer to take it stirred into a cup of Marmite, which itself, being made of autolysed yeast, will marry tolerably with dried yeast in flavour. Yeast tablets are fairly useless, as you can rarely take enough for them to be effective.
Yeast nutrient. Yeasts require small amounts of nitrogenous material and minerals for proper growth so in some circumstances it is recommended to add a yeast nutrient to the culture. Yeast nutrient may be bought or it can be made up as follows:
Citric acid 130 g (57%)
Ammonium sulphate 60 g (26.3%)
Potassium phosphate 30 g (13.2%)
Magnesium sulphate 8 g (3.5%)
Use this at the rate of 3 g per litre (¼ to ½ oz per gallon).
[Yeast – French: levure German: Hefe, Bärme Italian: lievito Spanish: levadura]
YEAST EXTRACT has been made since the turn of the century. It is not an extract in the usual sense of the word because it is not extracted from proteins an the yeast cells have been broken down. The breaking down can be done either by chemical treatment or biologically by autolysis, in effect salt-digestion by the yeast’s own enzymes.
The simplest way of breaking down the yeast is by hydrolysis which is brought about by warming it with dilute hydrochloric acid. A 1- 5% solution is used at a temperature of 30-100°C (86 -212°F) for anything from 30 minutes to 2 hours -the various different manufacturers use different combinations, time, temperature and acid concentration. When hydrolysis of the proteins to amino acids is complete, the hydrochloric acid is neutralized with caustic soda to form common salt, but the mixture is left slightly acid because a slight sourness helps to mask the bitter taste of yeast, which most people find nasty. Careful filtration helps to take out even more of the yeasty bitterness. The clear liquid is concentrated by boiling it at 60°C (140°F) under reduced pressure until the extract will set to a paste on cooling. Flavourings such as celery are frequently included to make the result more palatable. A more modern chemical treatment which modifies the proteins less, is to digest yeast with ammonia under pressure for some 7 hours. The ammonia is then allowed to evaporate.
The autolytic process is more complex and may involve adding sugar, blood, starch, gum arabic, phosphates and other substances. These processes are usually trade secrets.
Yeast extracts contain useful amounts of Vitamin B1, and B2, and a number of amino acids, plus choline and other essential food substances that are found in yeast, but they are not a complete protein food. Yeast extracts such as the British Marmite are sold for use as spreads or flavourings, or to make hot savoury drinks.
YELLOWS. See sugar.
YERBA. See mate.
YOGHURT. This sour milk product has been introduced to almost the entire world in the last four decades. It may have originated in Central Asia, but is now traditional over a large area of Asia and south-eastern Europe, although for historical reasons Americans and Britons usually associate it with Bulgaria. Even the characteristic bacterium is called Lactobacillus bulgaricus. At the turn of this century, Elie Metchnikoff (1845-1916) the famous Russian microbiologist, proclaimed yoghurt to be almost the elixir of life. His theory was based partly on the longevity of tough, yoghurt-eating Bulgarians and partly on the scientific fact that the lactic acid in sour milk discourages putrefactive bacteria. Metchnikoff lived at a time when poisons from the putrefying contents of the human gut were blamed for ill health, a process of auto-intoxication. So the Victorians helped nature with frequent and massive doses of castor oil, cascara and Gregory powder, not to mention an occasional enema. As a result, survivors still suffer from constipation. In spite of his yoghurt, however. Metchnikoff lived to be only 71. The yoghurt bacterium does not survive in the human gut (although that of acidophilous milk does better) and auto-intoxication seems to have been over-rated as a source of illness. What is sure is that yoghurt is much more rapidly and easily digested than raw milk, and its mild acidity falls kindly on the stomach. In an hour, only 32% of raw milk is digested as against 91% of yoghurt, and the lactic acid content helps in the assimilation of calcium and phosphorus. Yoghurt is correctly made from sheep’s, goats’ or cows’ whole milk, sometimes even from thin cream, but not, even in part, from reconstituted dried milk. It is a modern trick to add skim milk powder to give more body to the yoghurt. But then, the yoghurt of the supermarket does not have much likeness to the good yoghurt you can eat in Turkey. This is thick (it can be cut with a spoon) and never runny; it should be smooth, not grainy and with whey running out. It is even called ‘sweet’, although by its very nature it must contain some lactic acid. It should certainly never be very sour or bitter, although sour ‘old’ yoghurt is called for in some Indian recipes.
&n
bsp; Making Yoghurt
I) Apparatus.There are many gadgets on the market, ranging from metal boxes lined with heat insulator and containing a set of pots (including a little one for the starter) to electric yoghurt makers in which temperature is maintained by a heating coil and thermostat. All that is traditionally necessary is a pot or bowl, which should hold 1-2 It (1¾-3½ pt) of milk, a plate (or a sheet of cling film) big enough to cover it, and some wrapping to keep it warm. The wrapping may be a tin lined with cushions, a hay box or (as I use myself) an expanded polystyrene box of the type used for frozen foods. Wrapping in newspaper and then a blanket is a good makeshift. A vacuum flask is not recommended unless the yoghurt is to be turned out into a cloth after it has clabbered.
2) The starter. It is not necessary to buy a starter. A little taken from any pot of plain yoghurt will do as a starter, provided it contains live bacteria. Very little is needed – 1 teaspoon of starter per 1 It (1¾ pt) of milk- and too much starter makes sour or grainy yoghurt. The starter should contain Lactobacillus bulgaricus and Streptococcus thermophilus, which both grow well at 40-45°C (104-113°F).This is more than the ‘luke-warm’ that is usually recommended. The temperature should be measured with a thermometer (after stirring the milk to get the heat even).The classic, though much less reliable way is to dip in the knuckle of your little finger. When you can dip it in and count to ten slowly with some discomfort but without snatching it out with a scream, the temperature will be roughly right for yoghurt.
3) The milk Sheep’s milk and goat’s milk are normally used in the Middle East, which has comparatively few cows. The milk should be brought nearly to the boil before use or alternatively may be boiled for a while to concentrate it by reduction to a creamier state.
4) Method. Pour the boiling milk into the bowl or pot (which should first, like the spoon you will use, be scalded with boiling water). Leave it to cool until it reaches 45°C (113°F). Mix a teaspoonful or so smoothly with the starter, then pour it back into the milk and give a stir to distribute it evenly. Cover it with a plate and completely surround the pot with the insulation. Take a look after 5-6 hours and quickly wrap it up again if the milk has not clotted. Overnight is sometimes too long. When it has clotted, take it out of the wraps and put it preferably in a cool larder or, when it has cooled, in the bottom of the refrigerator.