As I mentioned earlier, concentrated grape juice is ideal for making into wine in its own right. These concentrates are now of high quality and produce good results, but they do not present so much of a challenge to the home winemaker as do country wines. However, that is not the main point here. Rather, my emphasis is on the use of concentrated grape juice as an additive to country wine. Any finished wine, no matter what the ingredients, should have that quality known as vinosity. That is to say, it should have those characteristics which make grape wines so enjoyable: aroma, body, and the way it tastes in the mouth and after swallowing.
Clearly the most obvious way of getting these qualities in a finished wine is to include some grape juice in a must, the "usual" quantity being 9 oz (250 g); both red and white concentrated grape juices are available in this size of container. However, it is far more economical to buy a large container and use it as required - the concentrate will keep in a refrigerator if it is transferred to a sterile glass jar and sealed tightly once the can has been opened. (For safety's sake, it is better not to store half-empty cans.)
Some recipes call for up to one pint (600 ml) of concentrated grape juice - notably flower wines, where the flower petals alone contribute nothing but bouquet and flavor to a wine. On the other hand, some recipes do not need any grape juice, the ingredients themselves being able to produce a balanced must and a high quality, vinous drink. Bananas are one fruit able to impart body to a wine, and they are frequently used as a substitute or addition to grape juice. Their own flavor, however, is rather pronounced. This can be reduced by discarding the skins, chopping the fruit into water and boiling for about fifteen minutes, during which time the pungent chemicals responsible for the strong banana flavor are driven off. The body which the resulting liquor provides in a finished wine is due to the presence of unfermentable compounds in solution - chiefly glycerol-like molecules, which give a viscous appearance. Such compounds may actually be produced by the yeast during fermentation.
This is said to be one characteristic of the Sauternes yeast strain, and the great body of Sauternes wine is certainly one of the wine's most notable features. Raisins or sultanas were the old-fashioned substitute for concentrated grape juice, and they are still useful and very suitable. One pound (450 g) of raisins or sultanas substitutes for one pint (600 ml) of concentrated grape juice. Note, however, that the high sugar content of concentrated grape juice means less granulated sugar need be added to a must. The appropriate amounts are indicated in each recipe. Although many winemakers insist on the addition of grape juice to all their wines, I would not be so dogmatic. It can and does help to produce better wines, yet there are many recipe hooks which make no mention of it at all. I have included it in the recipes where it helps produce a better wine. The different varieties of concentrated grape juice are described later.
SUGAR IN HOME WINEMAKING
In winemaking, treacle, golden syrup and brown sugar are best avoided, because they impart distinctive flavors which may conflict with the flavor of the basic ingredients. Honey can be used in mead recipes. The best sugar to use is pure, cheap, granulated white sugar.
Don't be confused by names such as sucrose, glucose, fructose and lactose. Sucrose is the chemical name of ordinary white sugar. Sucrose is said to be a "two-unit" sugar because each molecule of sucrose is made up of one glucose and one fructose molecule joined together. Thus it follows that glucose and fructose are simple "one-unit" sugars. Yeast begins its fermentation of sucrose by splitting sucrose into glucose and fructose:
C12 H22 011 + H20 => C6 H12 06 + C6 H12 06
Sucrose + Water => Glucose + Fructose
Glucose and fructose are then fermented by the yeast the way described earlier. (You will see that glucose and fructose have the same chemical formula; they differ in the shape of the overall molecule.)
It has been claimed that yeast can be helped by the winemaker if he or she supplies the sugar already split into glucose and fructose, i.e. inverted. This is actually open to question, but if you wish to try it yourself, do not buy glucose (which is expensive), but invert the amount of white sugar specified in the recipe by boiling it in water with a teaspoonful of citric acid for ten minutes. The syrup should be allowed to cool and then used in the preparation of the must; it will have a pale yellow color. The acid is not affected by the boiling and therefore takes the place of the same amount of acid in the recipe.
Lactose is another two-unit sugar, but with one important difference to sucrose: it cannot be fermented by yeast. This is because yeast does not produce the enzyme necessary to digest lactose. As far as the winemaker is concerned, the important point is that lactose can be used to sweeten a finished wine without any danger of the yeast restarting fermentation. This is discussed more fully later.
Although yeast lives off sugar in the must, it is killed or inhibited if the sugar is present at too high a concentration. Thus the ideal winemaking practice is to add the sugar in stages: for example, a proportion of the sugar is added at the start of pulp fermentation and the remainder when the wine is transferred to demijohn.
In the making of strong wines which require over 3 lb (1.35 kg) of sugar in each gallon (4.5 litres), the sugar is added in even smaller doses - a technique which helps the yeast to achieve very high levels of alcohol. But whether the sugar is added in stages or all at once, it must be completely dissolved and well mixed into the wine. Otherwise it will sink to the bottom and form a syrupy layer on the yeast sediment. The yeast will then without doubt be killed. There are two ways of avoiding this.
First, the fermenting wine can be poured onto the sugar in a sterile basin and stirred well until it is dissolved (but without heating the wine, for that would also kill the yeast). Second, the sugar may be added as a syrup. The so-called "standard" syrup is made by dissolving 2 pounds of sugar in 1 pint of boiling water. This produces a total volume of 2 pints of syrup. Thus the addition of 1 pint of this syrup to the wine will effectively add 1 lb of sugar in a form which can easily be mixed into the bulk. However, to reiterate the point, it is important that this mixing is done thoroughly, or the dense syrup will simply sink to the bottom of the fermentation vessel and kill the yeast.
Always remember that there is an increase in volume when sugar dissolves in a liquid. In UK non-metric units, dissolved sugar occupies a volume in pints equal to exactly half the weight in pounds. For example, 2 lb of sugar dissolved in a must occupies 1 pint in volume; 0.5 lb of sugar occupies 0.25 pint in volume. In metric units, the relationship is not so convenient: 1 kg of sugar increases the volume of the liquid in which it is dissolved by about 630 ml.
Whether you add the sugar in stages or all at once, remember to allow for this increase in volume. Final topping-up can be done when any foaming has died away and all the sugar has been added.
Original posting date
01 January 2018