Citramilic, galacturonic, glucuronic, gluconic, ketoglutaric, mucic, oxalic and Succinic acid are found in many fruit wines in trace amounts and contribute to TA - total acidity.
The proper acid level in a finished wine will also help to minimize effects of oxidation.
In oxidation, oxygen changes the chemical composition of the wine. When a wine is oxidized it discolors and browns.
When oxidized, the taste changes to something resembling cough medicine in extreme cases. Excessive acidity can also produce an intensely sour wine not fit for swine.
Fruits vary widely in acid content. Particular types of fruits fall within certain parameters - grapes for instance will have a certain range of acidity that they fall under. Tartaric and malic acid are about 90% of their acid content. However there are multiple variables that alter their acidic content- those grown in warmer climates will have a lower acidity and higher sugar content than those grown in cooler weather. Similar variables follow for all fruits.
The amount of fruit used also effects the overall acid content of the batch.Peaches, Apricots, Plums, Strawberries, sweet melons require 16 to 18 lbs of fruit to yield a gallon of juice. Grapes, Blackberries, Raspberries blueberries, currants, gooseberries, pineapple 12 to 15 lbs. Some recipes call for a higher water to juice ratio so this also is variable.
Combine the varying acidity of fruits, the amount of fruit used should make it apparent that controlling your juices acidity from the get go is vital.
How to Check the Acidity
Litmus papers are the simplest way to check the acid content of your juice [must] , they give you a rough but fairly accurate picture. They are easy to use and relatively inexpensive. For Home winemakers they are the most cost effective and efficient way to go.
Litmus papers are chemically-treated strips which change color when wine is added. The color indicates the pH. Dip the strip in the wine, wait several seconds, then matching the color of the litmus paper with those on the chart gives you a reasonable approximation.
Litmus papers aka pH strips are not without some drawbacks. They only you give a rough idea of the total amount of combined acids in the juice.
They do not tell you which acids are present. You may have an elevated amount of Tartaric acid in relation to others for instance - but the total amount of combined acids is still within acceptable parameters. This is a rare case - but would lead to a very tart even sour wine.
The most accurate method used to test the acidity is by titration. It sounds very technical - but it's actually very simple. Titration is a process to determine the concentration of unknown substances in a liquid. Titration kits measure specific acids within the juice. The kits themselves vary somewhat among manufacturers so it is best to read directions and manuals provided with individual kits rather than relying on generalized information.
Adjusting the acidity
Raising acid levels
Raising the acidity is done by adding acid - really ? - ya think ?! You simply add more acid. Acid Blends in a soluble granulated form are readily available and are are used by most winemakers.
They are also available individually -
Tartaric Acid, although found in abundance in grapes, is not found in all fruits. It is the dominant acid present in grape wines and controls their pH. It is sometimes added to wines where the primary base ingredient is lacking in tartaric acid.
Citric Acid Sometimes added to a post fermentation wine to boost acidity, it adds a fresh taste to the wine if used in moderation. If over used it can create an unwelcome synthetic taste as it conflicts with other components. Citric acid over time breaks down into other acids that degenerate into diacetyl which promotes oxidation and can destroy the flavor of a wine.
Malic Acid - Wines high in Malic Acid have a taste similar to green apples or unripened fruit. All fruits contain some level of malic acid , and a good portion is lost in the fermentation process. It is most commonly added to White wines in moderation as some people believe that it compliments their flavors. However I would not suggest adding it to any others as it has no true advantages over a balanced blend.
To Lower Acidity
You can dilute it with a mixture of sugar and water. 4 cups of sugar per gallon of water. This must be done prior to adding yeast. If you've already added the yeast tsk tsk tsk - shame on you.
Acid neutralizers are available commercially but seldom needed. They generally consist of calcium carbonate, potassium bicarbonate or acidex.
Calcium Carbonate as well as potassium bicarbonate reduces the sharp taste and unpleasant tartness by neutralizing acids and causing them to drop out of the wines solution in the form of tiny crystals. Calcium Carbonate is added before racking and the acid reduced wine is simply racked / siphoned off the sediment. One teaspoon of Calcium Carbonate per gallon of wine, will lower the total acidity (TA) by .10% tartaric.
You can also wait till after fermentation and dilute the wine with a similar wine. Some people add more water - if you're fond of Kool Aid go for it.
Acidex is another product that reduces the acidity of wine. Wine must be Clarified before it can be used. Acidex is processed calcium carbonate, it is double-salt seeded and designed to reduce both tartaric and malic acids in must or wine . Calcium Carbonate only reduces tartaric acid. Double salted is a solution formed by crystallizing a solution of the two salts.