Fruit composition

Qualitatively, the composition of different fruits is roughly the same, but quantitatively, huge differences can be observed depending on the fruit nature, but also the variety, le climate, the mode of culture...

The substances of interest for the wine maker are:

Water: 80-85%.

Fermentable sugars: sucrose, glucose, fructose (20-200 g/L).

Non fermentable sugars et polyalcohols: sorbitol, inositol...


Acids: tartaric, malic, citric (2-45 g/L).

Pectin [ Mixture of methylated polygalacturonic acids. By enzymatic hydrolysis, the pectin releases toxic methanol. It forms a net that traps the juice, rendering it viscous, so decreasing the yield at the pressing stage. ] .

Proteins, amino acids, food source for yeasts that will transform them in other substances.

Tannin [ The word tannin applies to various badly defined compounds, often polyphenolic acids esterified by a sugar. The tannins are very widespread in a lot of plants, mostly barks, fruits, tree leaves, oak wood...
The oenological trade tannin is mostly extracted from oak apple, sometimes also from grape skin.
The tannin has a typical astringent savour and a characteristic subtle odour. It is an amorphous pale yellow to brown powder. The tannin is essential in a wine: it is necessary for the wine clarification (min. 3 g/10 L juice). It forms insoluble compounds with proteins and metallic ions, starch and a lot of alcaloids. It also contributes much to the wine keeping. The tannin content of wines varies from 350 mg/L in white wines up to more than de 3 g/L in red wines. Ageing wines in oak casks increases their tannin content. ]

Flavouring matters: the flavour conveys taste and odour to the fruit. It is a messy mixture of hundreds of different substances, most of them present as very small traces. It contributes to the fruity of a wine.

Dyes (anthocyanes).

Mineral salts: necessary for the yeasts life. Some fruits are rich in them, other not enough and it will be necessary to add some salts to the sap for the yeasts feeding.


Methanol: very ripe fruits always contain small amounts of methanol. It is formed by hydrolysis of pectin before fermentation.


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