IT is then that one needs to employ a fermentation trap. This is a simple device, being in effect an air-lock, and we illustrate what is undoubtedly the most popular and commonly used pattern, a glass U-tube with two bulbs.
This is inserted in the bung or cork of the fermenting vessel so as to be an airtight fit (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 lightly grease the glass trap's stem 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 glass 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 will 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 in the trap glycerine of borax, 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 the flies access.
The fermentation 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. Of this, naturally, we are wholly in favour!
The air-lock is also a valuable indicator as to when fermentation is finished.
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 the trap with quite a musical "blup . . . blup . . blup. " This, you will find, is quite fascinating to watch. 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 air-tight 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. Rubber bungs are best; corks need to be waxed.
There are several other patterns of air-lock on the market (we illustrate one or two), and you will eventually decide for yourself which you prefer, and may well even make your own. A plastic or glass 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 back into the wine, which is bad for the wine and worse for the temper.
This can be avoided by using two phials instead of one, and coupling them as shown in the diagram.
Two plastic tablet-phials of any sort will do (those such as yeast is supplied in are ideal) and you will also need some tubing such as is supplied for use with tropical fish tanks. This is easier to use than glass, because it is smaller in bore and can be bent to shape in hot water. The diagram is self explanatory; all joints, of course, must be air-tight. The pressure is allowed to escape by means of a tiny hole drilled in the second phial with a red hot needle or fretwork drill. (If small glass bottles are used cut a V-groove down the side of the cork instead.) The twin phials can be secured by means of sticky tape.
During fermentation carbon dioxide will bubble out through the solution as with other traps, but if the pressure in the fermenting vessel drops below that externally, the sulphite is sucked back only into the first phial, and not into the wine.
Another simple idea is to use an ordinary rubber balloon, stretching it over the neck of the bottle. 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.
We illustrate a kind of trap used on the Continent and becoming increasingly popular over here because it is made in clear, non-fragile material, and is unbreakable in ordinary use, far more so than the rather fragile glass models. It consists of a cup into which the tube from the fermentation jar rises, and inverted over the top end of the tube is another smaller cup. Sulphite solution is poured into the trap as shown, 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.
THE essential thing to realise about winemaking. is that the most important and central factor is the YEAST. 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.
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