Terminology
| Fermentation | Typically refers to the conversion of sugar to alcohol using yeast under anaerobic conditions. A more general definition of fermentation is the chemical conversion of carbohydrates into alcohols or acids. When fermentation stops prior to complete conversion of sugar to alcohol, a stuck fermentation is said to have occurred. |
| Hydrometer | A hydrometer is an instrument used for determining the specific gravity of liquids. It is usually made of glass and consists of a cylindrical stem and a bulb weighted with mercury or shot to make it float upright. The liquid is poured into a tall jar, and the hydrometer is gently lowered into the liquid until it floats freely.
The point where the surface of the liquid touches the stem of the hydrometer is noted. Hydrometers usually contain a paper scale inside the stem, so that the specific gravity (or density relative to water) can be read directly in grams per cubic centimeter. In light liquids like kerosene, gasoline, and alcohol, the hydrometer must sink deeper to displace its weight of liquid than in heavy liquids like brine, milk, and acids. In fact, it is usual to have two separate instruments, one for heavy liquids, on which the mark 1.000 for water is near the top, and one for light liquids, on which the mark 1.000 is near the bottom of the stem. The function of the hydrometer is based on Archimedes principle that a solid suspended in a liquid will be buoyed up by a force equal to the weight of the liquid displaced. Thus, the lower the density of the substance, the lower the hydrometer will sink. Some historians credit Hypatia of Alexandria with the invention of the hydrometer although there is little evidence to support this. |
| Must | The ‘must’ is what the wine is called during the different stages of fermentation prior to it becoming wine or fruit wine. |
| Specific Gravity | The density of a liquid relative to the density of water. Must should be prepared to a SG of 1.09 – 1.10 for a dry wine. |
| Stuck Fermentation | A stuck fermentation is where a fermentation has stopped before completion; i.e., before the anticipated percentage of sugars has been converted by yeast into alcohol or carbohydrates into carbon dioxide. Typically, a stuck fermentation may be caused by: 1) insufficient or incomplete nutrients required to allow the yeast to complete fermentation; 2) low temperatures, or temperature changes which have caused the yeast to stop working early; or 3) a percentage of alcohol which has grown too high for the particular yeast chosen for the fermentation. Corrections to stuck fermentations may include: 1) repitching a different yeast 2) incorporation of nutrients in conjunction with the repitched yeast; 3) restoration of accommodative temperatures for the given yeast. |
| Tannin | Tannins (mainly condensed tannins) is found in wine, particularly red wine. Tannins in wine can come from many sources and the tactile properties differ depending on the source. Tannins in grape skins and seeds (the latter being especially harsh) tend to be more noticeable in red wines, which are fermented while in contact with the skins and seeds. Tannins extracted from grapes are condensed tannins, which are polymers of procyanidin monomers. Hydrolysable tannins are extracted from the oak wood the wine is aged in. Hydrolysable tannins are more easily oxidised than condensed tannins. Recently, a study in wine production and consumption has shown that tannins in the form of procyanidins, have a beneficial effect on vascular health. The study showed that tannins suppressed production of the peptide responsible for hardening arteries. To support their findings, the study also points out that wines from the regions of southwest France and Sardinia are particularly rich in procyanidins, and that these regions also produce populations with longer life spans. |
| Wine | An alcoholic beverage made from the fermentation of unmodified grape juice. The natural chemical balance of grapes is such that they ferment without the addition of sugars, acids, enzymes or other nutrients. Although other fruits like apples and berries can also be fermented, the resultant "wines" are normally named after the fruit (for example, apple wine or elderberry wine) and are generically known as fruit or country wine. |
Note: If there is a term in this "how to guide" that you don't understand and would like further explaination please contact the cellar operator for clarification.