How Is Wine Made? | Let’s Start with the Grapes

From Grapes to Glass Part 1

Jane Masters MW is Opimian’s Master of Wine


What impacts the flavours and styles? What makes a wine taste the way it does and how do I find more wines that I like? 


Wine is essentially fermented grape juice. The natural sugars in grapes are used by yeast as an energy source to live. During the alcoholic fermentation, yeast converts sugar into alcohol, producing at the same time aromatic flavour compounds and carbon dioxide. It sounds so simple — so what makes for the large variety of wine flavours and styles? In other words, what makes a wine taste the way it does and how do I find more wines that I like? These are questions I will be exploring over several articles, starting with the basic building block: grapes.


Most quality wines are made from grapes from the Vitis Vinifera species, of which there are thousands of varieties. These include varieties grown for eating and for winemaking (which tend to be smaller, rounder grapes with thick skins and high natural sugar). As grapes mature in late summer, they naturally build up sugar, acidity levels drop, and flavours develop. Hot dry climates generally produce grapes with higher sugar levels and lower acidity than cool regions. These parameters are monitored by winemakers when deciding when to harvest.


If all the sugar is fermented the resulting wine is dry. Approximately 18 grams per litre (g/l) of sugar produces 1% ethanol, hence the higher the initial sugar content, the more alcohol will be produced. Most dry wines range between 12 and 14% in alcohol. Fermentation can be arrested intentionally, or it can stop naturally, leaving residual sugar. Depending on the amount of sugar, the wine will be more or less sweet, ranging from several grams to wines with several hundreds of g/l, in the case of dessert and fortified wines.


Alcohol itself is sweet and this is why some dry wines can taste sweet. Try tasting a solution of 12% ethanol in water and you will find it decidedly sweet — with even higher alcohol, the sweetness is masked by a burning sensation. Alcohol also adds weight—– a feeling of richness or viscosity — it does not “feel” the same as drinking water. Water feels thin, while alcohol adds to the structure or shape of a wine. The balance between sugar, alcohol and acidity components plays an important part in how wines are perceived. A wine high in alcohol and low in acidity becomes flabby and lacks vibrancy. Acidity in wine is due mainly to tartaric, malic, lactic and citric acids which vary in their proportions. Each has a different acid strength and flavour. Wines with the same total acidity may be perceived differently depending on the ratios of different acids. While cool climates generally produce wines higher in acidity, in hot regions tartaric acid can be added by the winemaker.


Texture and weight can also come from phenolic compounds in grapes, most of which are in the skins and pips. For most white wines and many rosés, grapes are crushed soon after picking and the skins discarded so the flavour is coming from the pulp and juice alone. With red wines (and the current trend for orange wines made from white grapes), fermentation is carried out in the presence of the grape skins. Tannins and other phenolics add structure and texture to a wine, giving wines an ability to mature. Yet tannins can also have a drying or astringent effect on the tongue as they react with saliva in the mouth (think stewed tea and the skins of walnuts). A certain amount of grip adds length and presence, too much and the wine becomes aggressive. Grape varieties such as Pinot Noir are relatively low in tannins whereas Cabernet Sauvignon and Syrah have higher levels.


Wine is usually more aromatic and flavoursome than the fresh grapes used to make it. Wines contain thousands of aromatic components produced by yeast from non-aromatic molecules in the grapes. Some of these may be present in miniscule amounts yet still have an impact on wine flavour. Some may be common to all wines, and others are distinctly characteristic of a particular grape variety. For instance, Sauvignon Blanc displays passion fruit, gooseberry or cat pee aromas and Cabernet Sauvignon is associated with blackcurrants. How grapes are grown, the climate and level of ripeness has a bearing on wine flavour and intensity. Taking Sauvignon Blanc as an example, picked earlier it has greener, grassy, more pungent aromas due to methoxypyrazines. Left on the vine a bit longer, more grapefruit and passion fruit aromatics are produced from thiols. Deciding when to pick the grapes clearly impacts not only the alcohol and acidity level of the wine but its flavour potential. How this potential translates into the flavour of wine produced depends on how the grapes are subsequently handled… but that’s for the next part of the story.