Grain Alcohol See Neutral Spirit.

Galactonuric Acid A weak acid which forms long chain polymers which, when esterified with methyl alcohol, becomes pection.

Galactose A sugar which is of importance to the milk-drinker. One molecule each of galactose and glucose form lactose - the sugar of milk. This sugar is used in winemaking to sweeten wines, since wine yeasts cannot metabolize it.

Gallic Acid One of the tannins. Together with catechol and ellagic acid it is responsible for most of the astringency in a red wine. As it readily combines with gelatin, it follows that fining with this agent will remove this acid and produce a smoother softer wine.

Gallon The basic unit for winemaking in the US, Canada and the UK. Care must be taken between the different volumes of US (3.8 L) and Imperial (4.5 L) Gallons.

Gallon, US consists of 8 pints, each of 16 fluid ounces. One gallon US equals 0.83 Imperial gallons; or 3.78 liters.

Galvanized Iron is made by dipping clean iron into molten zinc. This zinc covering forms carbonates by reactions with the atmospheric carbon dioxide. Since carbonates are soluble salts, they will dissolve if in contact with an acid medium, such as wine. Apart from causing hazes, the use of such containers is to be deprecated, as zinc is a toxic metal.

Gas A chemical state, in which an element or compound is in a fluid state. Unlike liquids, gases have no definite shape or volume. They are all soluble to some degree in water; hence tap water contains oxygen which can be utilized by an unestablished yeast colony.

Gay Lussac A French chemist who was the first to hypothesize the fermentation equation; one molecule of sugar yields two molecules each of alcohol and carbon dioxide. Also the name given to the Continental scale of alcohol content. One percent alcohol equals 1 percent Gay Lussac.

Gelatin, Fish See Isinglass.  

Glass A translucent, non-reactive substance which is ideally suited to winemaking, since it has no taints to confer on a wine (so long as it is clean). See Carboys. See Secondary Fermenters and Accessories

Glass, Maturing in Unlike wood, glass has no pores in it to allow access of oxygen to the maturing wine. The only oxygen it receives is in minute amounts through the cork, and at racking times when it receives such large quantities as to be in danger of over-oxidation. However, despite this, for the average amateur glassware is still the best material, if not wishing to become involved in cooperage. But, extra time will be required for optimum oxidative changes, by comparison with casks.

Glasses Whatever may be said, there is only one glass suitable for drinking wine, one large enough to hold a reasonable quantity, with a slight tulip shape so that the bouquet does not escape to the atmosphere. There are designs for glasses of every type of wine, which are impressive but not essential. For the one glass person, it is hard to beat the tulip tasting glass. 

Glucose The most important hexose monosaccharide to winemaking. It is constituent of all disaccharides encountered in winemaking and in long chains it forms starch, cellulose and dextrins. Once released from its disaccharide, glucose enters the fermentative pathways to yield alcohol. Residual sugar (sweetness) in a wine is usually glucose or fructose.

Glyceric Acid One of the substances produced as a step in the metabolism of sugars. A hexose is broken down to two three-carbon sugars (trioses), which are then changed to glyceric acid or glycerin. The latter remains in the wine unchanged, while the glyceric acid continues in the fermentation pathway.

Glycerin of Borax See Borax, Glycerin of.

Glycerol The chemical name for glycerin.

Glycogen All living things store food. Yeasts are like man in that they store it as glycogen, which is composed of long chains of glucose.

Grain All cereal plants yield grain. They are of limited value in winemaking, since their main use is in giving body to a wine, and bananas or grape concentrate are both far superior. Cereals contain starch and, to prevent hazes from this, amylase must be used. Grains are low in acid so that assay and correction are needed. Also, they are low in nitrogenous salts, so, if nutrients are not used, the resultant wine will be high in fusel oils and hangover potential. Do not believe it when told that cereal wines get stronger after maturing. Once a wine has finished fermenting its alcohol content will not change (unless fortified).

Grain for Body tend to confer an unpleasant bouquet and taste on a wine, so that it is better to use bananas or grape concentrate instead.

Graisse The French word for Leuconostoc infection.

Gram The metric unit of weight which is defined as the weight of 1 cc of water at 4¦C. It is about 1/30th of an ounce. See Appendix XII.

Granulated Sugar See Sucrose.

Grape Concentrate for Body and Vinosity Most amateur wines will benefit from a few ounces of grape juice per gallon. Depending on the wine style planned, the amount will vary from 420 ounces per gallon, the light bodied requiring less, up to the full amounts of clarets, dessert or port type wines  See Additives

Grape Juice fermented produces white wine, irrespective of the color of the grape, indeed, much of the French white wine is made from red grapes. Red wines are obtained by pulp fermentation of red grapes.

Grape Tannin See Tannin.

Grapes To the amateur winemaker, the grape is merely another ingredient for wines. To the snob, they are the only ingredient for wine. It is incontrovertible that grapes as a lone ingredient produce the best wines, but country wines at least as good as lesser vintages can be produced from the garden. Even though the grape does not require blending with other ingredients it may still in poor years require chaptalization. One the whole, grapes have sufficient acid, nutrients, sugar and water to produce wines without any additions except for the yeast.

Gravity is not a true scale of measurement, but is used as an abbreviation of Specific Gravity. It is the amount by which the Specific Gravity is above or blow 1.000; i.e., a Specific Gravity of 1010 is a gravity of 10, while a Specific Gravity of 0.996 equals a gravity of û4.  See Appendix VI

Green Vegetables can be used as a base ingredient for country wines. However, acid and nutrients are essential, since these plants are lacking in both.

Green Vegetables, Preparation of Like most vegetables, these require boiling for about half an hour before blending the must. Most vegetables wine require long maturing.

Gums are complex carbohydrate compounds which, if present in a wine, will cause a haze. They are broken down by pectic enzymes.