See the notes (and example) below the tool for some tips concerning simplified sugar, water and acid corrections.

Musts are produced by crushing fruit or grapes. Here we assume all stem materials have been removed.

Tannin is found in grape skins and in the skins of a few fruits like blueberries.,loganberries and blackberries. Wines made from certain fruits do not have significant amounts of tannin. If the wine being fermented is red, and the fruit is low in tannin, grape tannin should be added, particularly if the wine will be high in alcohol and acidity for wine stability and a balanced taste. Addition of tannin allows minimal amounts of sulphite to be added in order to provide stability. If the wine being made is white or rose, then tannin is not normally added. But in this case, to prevent spoilage and oxidation, the amount of sulphite that is added should be the correct amount for a white wine. The guidelines produced by the sulphite tool may be used. A normal nutrient adddition should be made when making fruit wines. For red wines from low-tannin fruits typically one can add 1 teaspoon (5 [ml]) per every 5 liters of must before fermentaion. See the fruit wine design tool for more accurate amounts to add to red wines made from different types of fruit (or mixtures). Many fruits contain pectin (especially apples). Fresh pectic enzyme may be added to prevent hazes. Use the amounts recommended in the fruit wine design tool or follow the recommended amounts (see package etc.) for the enzyme you are using.

Basic Sugar and Acid Corrections Tool for Musts

Increasing the amount of sugar in the must will increase the juice's specific gravity (SG) and the alcoholic strength of the finished wine.

Increasing the amount of water in the must will decrease the SG and alcoholic strength and will also decrease the total acidity of the finished wine.

If total acidity has to be reduced by the addition of water, then some added sugar may be needed to maintain a reasonable amount of alcohol. Remember that at least 10 percent alcohol by volume is required to protect the wine from spoilage organisms. And the higher the alcohol level the more stable the wine will be. Remember also that wine should contain at least 6 grams per liter (measured as tartaric acid equivalent) of total acidity to prevent a dull taste and to protect against organic spoilage. White wines are more subject to spoilage and typically have a few grams more per liter (7 or above). Another type of acidity measurement is know as "pH". This is of even more importance in preventing spoilage, but in the case of pH, low values are better. Another tool (the sulphite tool) provided for calculating reasonable amounts of sulphite. It uses the pH (if available) to determine optimal amounts of this vital addition (potassium metabisulfite) which assists yeast to compete with bacteria and molds, prevents spoilage and reduces oxidation.

Increasing the amount of tartaric acid (or acid blend) with increase the total acidity of the finished wine by the amount shown. It is assumed that the must contains mainly tartaric and malic acid (the usual composition for grapes). For citrus or other types of fruit, it is better to use the fruit wine composition tool in order to find the amount of acid, sugar and water to add. This is because fruit other than grapes typically contain acids that are partly or entirely consumed by yeast in the fermentation. In addition certain other vital components such as yeast nutrients and tannins are not present in most types of fruit. Fruit wines are best made by recipes based on the experience of experts.

Each type of wine yeast has a particular level of alcohol which it can tolerate before it stops fermenting. Some special types of yeast can reach over 20 percent alcohol, particularly if the extra amounts of sugar required to do this are fed slowly into the secondary fermentation and other conditions such as nutrients, temperature and acidity are close to optimal. It is much more usual for yeast to stop fermenting at about 15 percent alcohol.

If sugar remains when the yeast stops fermenting, the wine will be sweet. Most producers of wine yeast make this information available. Ask where you buy your yeast if this information is not available on the package. Many books contain charts or tables with this type of data. See our book reviews for examples. The tool for simple sugar and acidity corrections uses the input (or default) fermentation limit to predict the finished wine's sweetness (in the usual units of grams per liter). Remember that each 1 gram per liter means 0.1 percent (by weight) of residual sugar. See also the tool for measuring percentage alcohol of a finished wine which attempts a more sophisticated prediction of residual sugars.

Example 1: "Wild" grapes with high acidity and low SG

We discover some wild (possibly native North American) red grape vines while camping and gather some to conduct a wine making experiment. On crushing, we discover that the grapes produce a must with a specific gravity of 1.052 and a total acidity of 12.0 grams per liter. The must volume is 37.5 liters. We plug these values into the correction tool and experiment. Because of the high acidity, we turn on the malolacic fermentation (check box) as this will help reduce acidity. We add water to reduce the acidity and sugar to increase the alcohol using the sliders. We find that if we have add about 14 liters of water and 8.2 kilograms of sugar the predicted acidity becomes about 6.5 and the potential alcohol about 12.6 percent. Uncheck the malolactic box to estimate the final acidity if malolactic fermentation does not occur. In order for malolactic fermentation to occur, the pH must be suitable, the aging temperature moderate to warm and the sulphite levels low. The sulphite tool makes predictions regarding the possibility of malolactic fermentation based on amounts of sulphite added provided that a pH reading is available. Since the grapes are red,there is probably plenty of tannin available (even with the added water) but we will add yeast nutrient in the amounts recommended on the nutrient package (or instructions). It would probably also be a good idea to add perhaps a half liter of grape concentrate. As a suggestion, add the concentrate first and then take new SG and acidity measurements. Then use the new measurements in the corrections tool. Remember, a measurement is always superior to a calculated prediction ! The advanced corrections tools permit predictions including concentrate additions.

Example 2: "Hot" California grapes with low acidity and high potential alcohol

We obtain 6 "lugs" (about 98 kilograms) of very ripe red California grapes. We carefully discard any unsuitable grapes. After crushing (stems removed) we get about 67 liters of must. The SG is measured at 1.109 and the total acidity at 4.8 grams per liter. These numbers are entered into the corrections tool which predicts 15.3 percent alcohol. The yeast that we prefer could be inhibited by this high potential alcohol resulting in a stuck fermentation. Our taste preference is also for less alcohol and a more balanced wine. We will prevent malolactic fermentation with suitable sulphite additions (see the sulphite tool) so we leave the malolactic box unchecked, By experimenting with the sliders, we discover that by adding 14 liters of water and about 160 grams of tartaric acid we should get a wine with about 12.5 percent alcohol and 6.5 grams per liter total acidity. We add tartaric acid rather than acid blend as insurance against low acidity caused by an unwanted malolactic fermentation. At the alcohol level predicted, any precipitation of potassium bitartrate will not reduce the acidity below critical levels (in terms of total acidity). The tool calculates final acidity including an estimate of bitartrate precipitation. We add yeast nutrient according to the nutrient's instructions and sulphite the must at crush and when racked from gross lees etc. to prevent malolactic fermentation (see sulphite tool).