Madeira A generic name given to wines which are heated prior to maturation. The heating processes cause Caramelisation of the residual sugar.

Maderization See Caramelisation.

Malic Acid The principal acid in applies, whence it gets its name. This is one of the main acids in grapes, being especially prevalent in the unripe fruit. As ripening occurs the malic acid content falls. In some of the northern vineyards the malic acid level never falls greatly, so that the malo-lactic reaction is encouraged. Malic acid is a bitter acid and if predominant will produce a sharp wine. Its use is chiefly in esterification.  

Malo-Lactic Reaction and Bottle Fermentation Sometimes the malo-lactic fermentation occurs after bottling. If it is discovered, the wine should be put back under air-lock to prevent explosions. If a petillant wine is wanted, then the wine should be racked into clean (non-sulphited) champagne bottles where there is no danger of the pressure breaking the bottles.

Malo-Lactic Reaction, Conditions for A young wine which has a high malic acid content is the first requirement. It must not have been filtered or sulphited (the bacteria will be removed by such a process), and the wine should be dry. Any residual sugar will be broken down to the bitter sugar mannitol.

Malt Barley, after partial germination and kilning, is known as malt. It is used in some recipes, but its main use to the winemaker is as the dried extract for preparing starters.

Maltose The principal sugar of barley which is only slowly fermented by wine yeasts.

Mannitic Infection occurs in stuck ferments at high temperatures. The bacteria (one of the lacto-bacilli) breaks down fructose to mannitol. Prevention is by ensuring sufficient acid in a well prepared must and protecting against infection. There is no cure for this condition and it is best to discard the wine, should it occur.

Mannitol A sugar with a bitter taste produced by on of the lacto-bacilli. If a sweet wine undergoes a malo-lactic fermentation, there is a chance that mannitol will be formed.

Mannose A sugar which is commonly found as a constituent of plant protein. It is fermented by wine yeasts.

Marc The French word for pulp after it has been pressed. See Brandy.

Marriage During maturation the constituents of the embryonic wine interact, so that when it is ready for drinking, all the components harmonize with each other. This process is somewhat poetically called the marriage

Maturation and Acidity Apart from the bactericidal effect of a correct acidity, the proper acid balance will benefit the wine during maturation as the succinic and malic acids esterify to form compounds which will eventually aid the bouquet. A wine which is low in acid will not improve. Instead it may develop a medicinal taste. An over-acid wine will mellow during maturation and although a lot of time is needed it should eventually become drinkable.

Maturation and Esterification A long, slow process which involves the joining of acids and alcohols to form compounds which play a large part in flavor and bouquet. The acids required for esterification are malic and succinic. The latter is a by-product of fermentation, but its addition in small amounts will certainly aid the process. Ester formation takes place largely after bottling ( it is a reduction process) and it is to encourage this reaction that quality wines should be allowed a year or so in bottle before tasting.

Maturation and Oxidation See Oxidation and Maturing

Maturation and Reduction See Reduction.

Maturation and Tannin During maturation, the tannin content of a red wine falls. Some is oxidized; some joins with protein and other constituents in the wine; and some will precipitate out of the wine. The overall effect of this will be the lessening of the astringency and, since the tannin content takes a long time to fall to a palatable level, a better quality wine, due to a longer period for other constituents to marry with each other.

Maturation in Bottle See Bottle Maturing.

Maturation in Bulk A wine matured in small carboys will mature faster than in large ones. This is because the volume/surface area ratio dictates the amount of oxygen that can be absorbed by the wine for oxidation reactions. Ideally maturing should be a slow process to allow reactions to occur and the old and new compounds to blend together. Thus a carboy with a large volume will supply less oxygen and the process will take longer.

Maturation in Cask See Cask Maturing.

Maturation in Glass Provided the wine receives oxygen by, firstly, a cork bung (although the amount is small it is significant), and, secondly, by regular racking, it will mature satisfactorily. The end result will not be as good as with cask maturing but it will be quite acceptable. The possible reason for this is that the wine matures at an uneven rate, unlike the slow constant rate in cask.

Maturation Temperature should ideally be about 55¦F (10¦C). Warmer than this will mean that chemical reactions, which go faster at a higher temperature, will progress too fast, with the result that the wine will mature too quickly for quality.

Maturation, Chemistry of During this time malic and succinic acids are esterified; fusel oils broken down to acids and aldehydes; small amounts of acetic acid formed; and aldehydes and alcohol join to form acetals.

Maturation, Conditions required The bottle cellar is ideal for maturing, provided that it is dark and dry and cool.

Mead Derived from a Greek word meaning wine, it has come to mean a drink made from fermented honey. Its relatives, such as metheglin (spied mead) and melomel (fruit and honey) are not accepted as mead by purists.

Measures For winemaking, it is necessary to be able to measure weight to an ounce accurately (less than this should be performed with solutions or beam balances). Volume measurement requires 100 ml calibrated jars, containers, gallon jugs. Most of these can be borrowed from the kitchen. See Appendix XII for weight and measure conversion charts.

Mechage The French word for burning sulfur wicks in barrels.

Medicinal Taste An off-flavor, variously described, which once tasted is never to be forgotten. It is due to a lack of acid in the must. Prevention is by acid control in the must. A cure may be possible by sweetening, but the safest treatment is discarding the wine.

Medium Not the genie who predicts the quality of future vintages, but a solution or jelly for growing yeasts. A medium must contain foodstuffs, nutrients and vitamins and must be sterile.

Melomel A wine made with fruit juice and honey.

Meniscus All liquids have a surface tension which is the property which keeps them liquid. Without this, they would become gases. The effect of this is to cause the liquid to rise or fall slightly where it meets the walls of a container. It is important to ignore the meniscus in S.G measurement. The S.G is taken at the point where the main level of the liquid lies and not at the top of the meniscus. Failure to appreciate this may give rise to an error of 5-6 in the gravity.

Meso-Inisitol A compound which is not a true sugar, although it has a similar structure. It is important to vitamin to the yeast and the use of malt in the starter will supply sufficient.

Metabisulphite The chemical radical from which Campden tablets are made and which is the storage form of sulfur dioxide, the active sterilizing agent. When placed in water it is broken down to bisulphite which then liberates sulphur dioxide gas. The word is usually abbreviated to sulphite or bisulphite. The subject is fully discussed under the former heading.

Metabisulphite, Sodium and Potassium The commercially available preparations of sulphite are sold in powder forms as the sodium or potassium salts, or as Campden tablets (potassium salts). See Campden Tablets.

Metabolism The term given to the series of chemical reactions in which foodstuffs are broken down to yield energy and waste products

Metal Haze See Casse, Metallic.

Metal, Dangerous Do not use toxic metals such as lead and brass. Non-toxic but haze causing metals such as copper and iron should also be avoided.

Metal, Fining of is possible to the professional using EDTA (ethylene diamine tetra-acetate). This method is safer than the one involving the use of ferrocyanide, which is a deadly poison. For the amateur it is sometimes possible to effect a degree of cure with the use of 5% citric acid. 

Metallic Casse A haze due to metallic compounds entering solution in a wine

Metallic Taste A descriptive term for the distinctive off-flavor due to metal contamination. A wine so affected does have a definite taste of metal. See Diagnosis of Faults

Metheglin Spiced mead. The word is derived from the Welsh word meaning medicine.

Meths A fuel composed of ethyl and methyl alcohols and a foul smelling substance, pyridine. Despite its toxicity (see Alcohol, Methyl), it is still drunk by some addicts. It is used in winemaking as a test solution for the presence of pectin.

mg The abbreviation for milligram (one-thousandth of a gram).

Micro-Organism Any unicellular plant or animal which cannot be seen by the naked eye. They have a wide range of functions. For the winemaker, two classes of importance are the yeasts and the bacteria.

Mildew An infection of plants which, if it affects grapes, will ruin the crop. See Botrytis Cinerea ; See Mould.

Mineral Any inorganic salt or metal. They are of importance to yeast reproduction and metabolism as vitamins, catalysts or co-factors. See See Calcium ; See Magnesium ; See Phosphates ; See Potassium ; See Sulphite