lunes, 13 de agosto de 2012

Making Home Made Wine (Fermentation)


FERMENTATION OF WINE

By C.J.J. Berry (Editor, The Amateur Winemaker)


The alcohol which we seek as an ingredient of our wine is a by-product of the yeast’s process of self-reproduction.

When the yeast is put into a sugary solution, it begins to multiply vigorously, and in the complex chemical processes which ensue, the sugar is converted roughly half to alcohol by weight and half to carbon dioxide (the bubbles).

The first, the aerobic (‘with air’) fermentation, will be comparatively vigorous, perhaps with some froth, but may last only five or six days. The wine will then settle down to the secondary, anaerobic (‘without air’) ferment, which will be much quieter and which towards the end may be barely discernible. This may last two, three, or four months, or even longer.

Temperature plays an important part. Above 38°C (100°F) the yeast will certainly be killed; at too low a temperature it will ferment only very slowly, if at all. A fermentation should be started off at about 21°C (70°F), the secondary fermentation should be at about 16°C (65°F), and the finished wine should be stored at 10°C to 13°C (50-55°F). So the temperatures are easy to remember - 20°, 15°, 10°C (or 70°, 60°, 50°F). A slow quiet fermentation usually produces better wine than a fast, over-vigorous and short one, and there is no need to be fussy within 2°C.

During the secondary fermentation it is wise to employ a device called a fermentation trap, or airlock, which both cuts off the air supply to the yeast and protects your wine from bacterial infection, of which more later.

As the fermentation proceeds, so the alcohol content increases, until finally it reaches a concentration (usually about 15-16 per cent alcohol by volume) which is such as to inhibit the yeast, preventing any further activity. Any sugar still left in the wine then remains only as a sweetening agent. Once the fermentation is finished the wine will not normally become any stronger no matter how long it is kept, although it will undoubtedly mellow with maturity.

THE FERMENTATION TRAP

It is thru that you need to use a fermentation trap, or airlock, to protect the ferment; it will let gas pressure escape but admit no air.

The trap, incidentally, has a secondary purpose. The yeast, for the reproductive process which it first employs, needs oxygen.

When, by means of the fermentation trap, we cut off its air supply, we force it to turn to a secondary method of self-reproduction which it can use without oxygen, and which is appreciably more productive of alcohol.

The airlock is also a valuable indicator as to when fermentation is finished. It is a simple device. The U-type with two bulbs and the cup type. Both are now made in plastic; the former can still be bought in its glass form. Whichever sort you use, it is inserted in the bung or cork of the fermenting vessels so as to be an airtight tit (this is important, or the lock will not work), and a good tip is to use rubber bungs rather than corks to ensure that there is no leakage.
It is advisable to grease a glass trap’s stem lightly and hold it in a thick cloth when pushing it home, to avoid the risk of breakage and a hand badly cut by jagged glass. The bottom of the stem must be above the level of the fermenting liquor; a half to three-quarters of an inch is normally sufficient, as long as the liquor is not frothing so vigorously as to force it out through the trap.

The U-bend of the trap is then filled with water, to the bottom of the bulbs, and in the water is dissolved one-eighth of a Campden tablet. Thus, even if a vinegar fly gets into the water and meets an untimely end, your wine will be safe, whereas if you have plain water in your trap it may become infected with the bacteria from the dead fly. In that case, since the inner end of the water is in aerial contact with your wine, it is still possible for your wine to be infected. So always use this small quantity of sulphite in the bend of your traps, and renew it every month or so. Alternatively, use glycerine of borax in the trap, which is less volatile and will not deteriorate. Yet another method is to use plain water, but to plug the top of the trap with a tiny tuft of cotton wool to deny dust and flies access.

As the wine ferments, it gives off carbon dioxide, which quickly builds up a pressure within the fermentation jar or bottle, and then pushes its way through the solution in a U-type trap with quite a musical ‘blup. . . blup. . . blup'. As the ferment proceeds, the bubbles will pass ever more slowly until finally the solution in the trap remains poised and no more gas passes. It is then a good idea to move the jar into a warm room for five or six days to see if any further activity develops. If not, it can be assumed that the fermentation has finished, but make sure that your cork or bung is still airtight and that gas is not escaping through it or from its junction with the tube of the trap, or naturally the trap will not work.

The cup type of lock has become increasingly popular in recent years and is available in several patterns. Many like this type of lock because it is not so fragile as the glass bubbler, it consists of a cup into which the tube from the fermentation jar rises, and inverted over the end of the tube is another, smailer-diameter, cup. Sulphite solution is poured into the trap and when gas is given off by the ferment it lifts the inner cup up and down to escape beneath its rim, through the solution. As with the glass bubbler, you need to inspect the trap from time to time to make sure that it still contains plenty of solution, and that too much has not evaporated.

MAKING YOUR OWN

There are several other patterns of airlock on the market and you will eventually decide for yourself which you prefer, and may well even make your own. A plastic tube leading down into an aspirin bottle or yeast phial containing sulphite solution and secured to the fermenting vessel with sticky tape will answer quite well as long as you remember to remove the phial before uncorking the jar. If you do not, the sulphite solution will be siphoned back into your wine as you withdraw the cork and thus reduce the pressure inside the fermenting bottle. It should be noted that this minor disaster can also happen if the pressure inside the fermenting vessel happens to drop below that of the surrounding atmosphere; the sulphite in the trap will be sucked into the wine, which is bad for the wine and worse for the temper.

Another simple idea is to use an ordinary rubber balloon, stretching it over the neck of the jar. The pressure of the gas will inflate the balloon, and when inflation ceases the ferment is finished. For wide-necked jars or crocks one can use a sheet of polythene, secured with a stout rubber band. This, too, will be bulged out by the pressure of the gas which will escape from beneath the band.

These ideas are quite useful in the initial stages of fermentation, when the must often tends to foam quite vigorously, and can froth out through an airlock and down the side of the jar, making an awful mess. True, it is easily cleaned up and the rinsed airlock replaced, but it is even simpler to take the precaution of using a plug of cotton wool or a piece of polythene plus an elastic band, which can be thrown away, instead of an airlock. It also helps to stand the jar on a tray, to collect any yeasty overflow, and to pop a plastic shopping bag over the whole to prevent any splashes on nearby walls. After four or five days the ferment will have quietened and you can have a final clean-up and insert a ‘proper’ airlock.

Some winemakers content themselves with plugging the neck o the fermentation jar with cotton wool throughout. It is an excellent idea for the first few days of fermentation, when the yeast needs plenty of oxygen to multiply, and when the use of cotton wool may simplify tidying up if you have an overvigorous, frothy fermentation, but it is not a good practice thereafter. As the fermentation slows, and the amount of carbon dioxide given off decreases, the possibility of infection by airborne bacteria increases and there is no visual indication as to how the fermentation is progressing. So it is always wise to employ some form of airlock, however primitive.

YEAST

The essential thing to realise about winemaking is that the most important and central factor is the yeast. The scientific name for yeast is Saccharomyces, or sugar fungus. Baker’s yeast is S. cerevisiae, and true wine yeasts are S. cerevisiae var. ellipsoideus. The whole of winemaking practice really comes down to the matter of providing ideal conditions for the yeast, a living organism, to thrive and multiply. To do that the yeast must have sugar, it must have warmth, it must have oxygen, it must have a certain amount of nitrogenous matter, vitamins, and some acid. The ideal ‘recipe’ will provide all of these; if any one of them is lacking the ferment may ‘stick’, or temporarily stop.

WINE YEASTS

One of the big strides which has been made in winemaking is that there are now available to the amateur many excellent varieties of special wine yeasts, in either culture or tablet form. Their value is unquestioned, for there are innumerable varieties of yeasts, all with different characteristics, and just as some are more suitable for baking or beer-brewing, so others are better for the production of quality wine. A good wine yeast has a high alcohol tolerance i.e. it will allow the wine to ferment further and be that much stronger before it succumbs. It will form a firmer sediment, making racking much simpler, and it will be less prone to impart `off´ flavours to the wine.

These yeasts are laboratory-cultured from the yeasts on the grapes in the place of origin, and it is great fun to experiment with them, and see the different nuances of flavour than they confer.

It is naturally advisable, when using these specialised yeasts, to employ them in `musts´ which will be sympathetic to them, i.e. a Port or Burgundy yeast in a red wine such as elderberry, sloe or damson, and a Champagne yeast in a sparkling wine. The beginner will do best, however, to experiment first with a good general-purpose wine yeast. You can also obtain a fairly good range of yeasts especially suitable for lager, beers and ales.

Many winemakers still adhere to baker’s or brewer’s yeasts, but it is a pity to do so without having tried some of the excellent true wine yeasts now on the market. They are certainly worthwhile for one’s ‘special’ wines and are by no means as expensive as they at first appear, since they can be propagated and carried on from one wine to another. Wine yeast, granulated yeast, yeast cultures, yeast tablets, baker’s yeasts, brewer’s yeasts ... all will make wine of varying quality, and which yeast you use is a matter of personal preference.

Wine yeasts are sold in various forms, granulated, as tablets, and as compounds complete with nutrients. Many of them nowadays are so good that they can be added direct to the must, and the fermentation will get going right away, just as it does with baker’s yeast.

Baker’s yeast, brewer’s yeast or granulated domestic yeast can certainly be added direct to the must, when the liquid is lukewarm (about 21°C). They will give you a vigorous and frothy ferment, which is very encouraging if you are a beginner in that you will know the ferment really has got going, but it does not make for high-quality wine. Much of the wine’s possible bouquet will be carried off with the rush of gas generated. If you wish to use such yeast, use it at the rate of 1 level teaspoonful per gallon.

But I firmly recommend you to start straight away with wine yeasts. The fermentation will be much less ‘showy’, and sometimes only just discernible as tiny bubbles round the periphery of the liquid in the jar, or by the movement in the airlock, but better wine will result.

Beginners often worry about exactly how much yeast to add but as long as you have enough to get the fermentation going reasonably quickly the quantity is not critical, since the first thing the yeast does is to multiply rapidly. Thus, when making, say, five gallons, you do not necessarily need five times as much yeast as for one. Either make up a starter bottle, or, if you are adding the yeast direct to the must, double or treble the quantity. Individual suppliers provide detailed instructions with their yeasts, so there is no need to worry; you will find it quite simple.

HOW YEAST NUTRIENT HELPS

To obtain the best possible fermentation the yeast, like most living organisms, must have both food and oxygen. Like human beings, it needs both vitamins and fresh air. The ideal medium for fermentation is pure grape juice, which contains all the nutrients, or foods, that the yeast requires, but some of the musts are deficient in them, and it is therefore wise to add a nutrient to give the yeast a ‘boost’, the nitrogenous matter.

You can obtain several good proprietary yeast nutrients from trade sources, but if you are likely to be making wine regularly and in reasonable quantities, it will pay you to make up your own. Buy a 250 g jar of ammonium sulphate BP (NH4)2S04 and one of ammonium phosphate (NH4)3P04 and use half a level teaspoon of each in each gallon of wine. This will provide all the nitrogen and phosphate that the yeast needs, and the chemicals will always be ready to hand in your cupboard.

The other invaluable nutrient which has a wonderful effect upon the vigour of a fermentation is Vitamin B1, or thiamine, as you can quite easily prove for yourself by adding it to some trial gallons. Buy it as tiny tablets (3 milligram size) from your chemist (they are sold under various brand names) and use them regularly following the recomendated rates per gallon.

This addition of nutrient to the must does certainly enable the yeast to carry the fermentation just that little further, and is a great help in the production of strong, dry wines, and in the avoidance of oversweet wines.

Other good general purpose nutrients to have by you are potassium phosphate and magnesium sulphate. Often, too, plain malt extract (not the cod liver oil variety) can be used advantageously at the rate of one dessertspoon per gallon to get a fermentation away to a vigorous start, but it is wisest to restrict this practice to red or dark, full-flavoured wines, since it will impair the flavour and colour of light, delicate ones.

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