Acidity is ability of a substance to release hydrogen ions upon dissociation in water. It is measured as a PH value, which represents the negative logarithm of the hydrogen ion concentration. The PH values range from 0 to 14; 0 being most acidic and 14 the least. PH of 7 is neutral, which means the solution is neither acidic nor basic.
Each organism has a well-defined acidic range and optimum PH value for ideal growth. For wine yeast, saccharomyces celevisiae, the PH range is between PH 3.0 to PH 4.0 with optimum around PH 3.5.
This is an acid loving microorganism.
The following table lists some of the common fruits with their approximate PH values:
Apples 3.0-3.4
Cherries 3.3-4.1
Lemons 2.2-2.4
Plums 2.8-3.1
Apricots 3.7-4.1
Grapefruit 3.0-3.4
Lime 1.7-2.0
Raspberries 3.2-3.6
Bananas 4.6-4.8
Grapes 3.4-4.2
Peaches 3.4-3.6
Wines 2.8-3.8
Blackberries 3.3-3.7
Jams 3.4-4.0
Pears 3.5-4.1
From this table, you can correlate the acidity of each fruit to the optimum PH range of the yeast.
Remember, the addition of sugar and water will dilute the acidity, which needs to be compensated.
Once you have prepared the must, measure the acidity using litmus paper. This is a simple, inexpensive, yet relatively reliable measure of acidity.
If the juice is low in acidity (high PH) adjust it using acidic fruits such as lemon or lime. You can also purchase a blend of acids from your wine supplier for this purpose.
For musts that are too acidic (low PH) you can adjust it by doing one of several things:
- Blend some of the fruit and lower acidity (high PH) to bring it to desired level;
- Dilute the must using water and sugar.
This is a preferred method since it is quite effective, as well as increasing the amount of wine being produced.
- Add 1 teaspoon at a time of buffers such as calcium carbonate or sodium bicarbonate (baking soda).
Wines low in acid will taste flat and uneventful. On the other hand, wines with too much acid will taste bitter with definite, pungent after taste. For this reason the acidity of must, hence wine, plays a critical role.
Some of the common organic acids found in fruit are:
- Tannic Acid (Tannin) – most abundant in grapes and oak trees; good cleaning agent in wines and produces a typical, pleasant, dry after taste. If too much, the wine will be bitter; If not enough, flat and tasteless.
- Ascorbic Acid (Vitamin C) – excellent antioxidant added to wine to prevent oxidation of alcohol.
- Citric Acid – most abundant in lime, lemon and berries; has a clean crisp taste. This is the favourite of them all. In fact, if you need to increase the acidity (lower PH) add lemon or lime.
- Tartaric Acid – main acid found in grapes. Small amounts improve the keeping quality in wine. Usually percipitates in form of tartrate salt. If too much, it produces a sharp, acidity flavour.
Bon Voyage
