(And Port Style Wines)

This tool also predicts residual sweetness etc.

Advanced Potential Alcohol Adjustment Tool

Temperature Adjustments. Hydrometers are calibrated to work at specific temperatures, typically roughly 15 C. Using uncorrected measurements taken at other temperatures may lead to errors and the tool will apply these corrections if the measurement temperature is entered. Brix measurements should always be made at the instrument,s calibration temperature (20C) but we recommend the use of temperature compensated instruments which are now available at reasonable prices. Once you use this instrument a few times you will not understand how you ever functioned without it !

Stems Stems (at least some) are often left in the must during the primary fermentation. They increase the must volume but not the final amount of wine produced. More important, stems introduce a great deal of tannin and other bitter substances. Powerful red wines with very high acidity and lots of alcohol are often fermented with a considerable percentage of stems left in the must. Typically, the wine produced may need to be aged five or ten years before it has "mellowed" enough to drink. If such a wine is not balanced by very high extraction of color and flavours it may never mellow ! So this type of winemaking is best left to those with the very best supply of noble grapes and the large amounts of capital required to cellar wines for several years. Some grapes may produce very high levels of tannin even with all stems removed. Certain types of grapes like tannat (used to make Madiran) have been deliberately developed with this property. Since a lot of tannin comes from the seeds, the amount of tannin in the wine may be reduced by removing the seed after two or three days of primary fermentation. Generally, the longer the seeds are exposed to the fermentation the more bitter the extraction products. This is why it is a good idea to limit the use of seed in a second fermentation (see making false wine). Unless you are able to measure tannin each day, only experience with specific grapes can guide you in the refined use of stems and seeds. Top winemakers often have a superior sense of taste and use it to detect subtle changes during fermentation. Human taste buds are sensitive to bitterness. Try tasting your wine during fermentation. If you experiment and keep accurate notes you too may become an exceptional winemaker. If you are a member of a winemaking group, you may be able to learn several times faster by tasting several fermenting musts and the resulting wines each year.

Fermentation Limits and Yeasts. Cultured wine yeast are able to survive much higher levels of alcohol than can most "wild" yeast found on grapes. They are also able to better resist the effects of sulphites making them much more compatible with modern winemaking methods. This means that cultured wine yeasts are the best insurance against "stuck fermentation's". If the yeast you use cannot convert all the fermentable sugar in the must (because the alcohol level reached inhibits them), the resulting wine will be sweet rather than dry. In some wines, this is what is wanted. But in most cases this is a serious flaw and can lead to organic spoilage. Some wine yeasts can ferment to over 20 percent alcohol ! Particularly if the extra amount of sugar needed to get this much alcohol is added over several days during the secondary fermentation. If the yeast that you are using has a maximum alcohol tolerance much different from the tool's default, enter the correct value in the text area provided. Then the tool will indicate conditions when you are likely to get a sweet wine by predicting a non-zero sweetness.

Port Style Wines Certain wines are only partly fermented. The fermentation is stopped by adding a strong distilled spirit (brandy etc.). In this case, the fermentation limit is low and is determined by the winemaker not the yeast. After the fermentation is terminated, the winemaking differs from that for a typical wine and you should consult a book for details (see our book reviews). Although this method typically leaves a lot of sugar unfermented, the wine is stabilised by its high alcohol level. If you want to try making this type of wine, you need to know how much spirit to add (and when) which is what the tool does (among other things) You will also want to predict certain final properties such as sweetness and the amount of wine that will be produced. The tool can make these predictions because it permits the specification of a maximum fermentation limit and the addition of spirits. It also predicts the must SG at the point that you will need to add the spirits (that is, at the fermentation limit chosen). Note that other major issues such as acidity also need to be handled differently. Since the tool permits the addition of concentrates and water before fermentation, it is recommended that total acidity level be tested again after all additions and before the primary fermentation. Since distillation of spirits removes most of the important acids found in wines, the winemaker will probably want ot start with a must of higher than normal acidity. Then when the spirits "dilute" the wine the final acidity reached will be lower. High alcohol levels mean that the wine's organic stability is less dependant on acidity so that in this case acidity mainly an issue of taste. Generally, higher amounts of residual sugar, require more acidity for a balanced taste. Yeasts experience stress under high acidity but since the fermentation alcohol level will never be very high, many types of yeast will perform well enough to make this type of wine. In order to make good port style wine, the winemaker needs to have a sound understanding of the fermentation fundamentals and clear goals (acidity, sweetness etc.) for the final product. Why not find out the sweetness, alcohol level and acidity or your favourite style of port and see if you can make a similar product.

Tartaric Acid and Acid Blend A wine's acidity is adjusted by adding either tartaric acid or a blend of tartaric, malic and citric acids. Since malic and citric acid may be entirely consumed during fermentation (particularly in malolactic fermentation) the choice of which to add can only be made in connection with decisions about malolactic fermentation. Citric acid is cheap but since it is consumed during fermentation the reasons for adding it before fermentation are subtle (at best). Fortunately, although some acids are consumed during fermentation, other very important ones such as succinic acid are created. This acid is responsible for giving wine its main characteristic "acidity taste". In addition, acetic acid (vinegar) is produced. Vinegar is often referred to somewhat politely as "volatile acidity". A tiny bit of volatile acidity may add to a wine's complexity but amounts detectable by taste are a major flaw. This is avoided by using modern sanitation and fermentation methods. Fortunately for winemakers, the total acidity of a wine ofen does not decline very much even when certain acids are lost. This is partly because the total volume of wine produced is quite a bit less than the volume we start with (remember part of the sugar escapes as carbon dioxide, there is some evaporation etc.) so that on a grams per liter basis the final acidity tends to take care of itself. Looking at acidity from a spoilage point of view, it is the wine's pH that is critical. Because wine is "buffered solution" of salts and acids (remember any of that chemistry 101 you took?) , if we start with a suitable pH we usually also end up with a suitable low pH. One thing that wine makers sometimes worry about is the precipitation of added tartaric acid in the form of potassium bitartrate. This happens because tartaric acid is less soluble in water containing alcohol (wines). This is the reason for the old rule of thumb which specifies that not more than two grams per liter of tartaric acid should be added to a must. The precipitation of bitartrate tends to happen slowly and is encouraged by lower temperatures. This is another good reason to age wine all winter in a cool place. The tool assumes an average amounts of bitartrate will be precipitated in producing an estimate of the wine's final total acidity. Remember, measurement of properties (like acidity) produce facts while calculated predictions are an educated form of speculation ! If you really need to know, measure the acidity after fermentation. Minor acidity corrections are sometimes conducted after fermentation. Any citric acid added at this stage may stick around and even add complexity to the taste (in small amounts).

Concentrate Strength The tool permits the addition of concentrate which is generally superior to a sugar addition but is also more expensive. If you do not know the strength of the concentrate the tool suggests a way to measure it. Alternately, you can always let the tool use its default concentrate strength value and do a quick specific gravity check before fermentation. Then, if necessary, do a fine adjustment treating the new mixture as if it were just another must.

Spirits and Units Spirits strength (brandy, vodka etc.) is most reliably stated in percent alcohol by volume. If the spirits you plan to use have a strength given only in "proof" units then you will need to determine which type of proof is being used. There are at least four types of proof in use (and probably several other variants). The tool permits the strength to be input in two different types of proof. Use the percent alcohol figure whenever possible. Spirits hydrometers can be purchased fairly cheaply and these will allow you to measure proof directly and (hopefully) indicate which system they use. There are several instruments available with more than one type of scale and this may require somewhat careful use.