Acidity, Alcohol & Sugar

Grapes nearing ripeness

We’re moving on to structure in the Oxford Course on Blind Tasting. The structure of a wine is generally a more reliable indicator for identification of a wine. Structural elements of a wine are present on the palate and don’t include aromas and flavours. They include: acidity, alcohol, residual sugar, body, oak, tannins and length. This week we focused on the first three.

Acidity, alcohol and residual sugar in a wine are all related to each other. To generalise, as the grape ripens, its sugar levels (glucose and fructose) increase and its acidity (tartaric and malic) decreases. Harvest time is thus important in attempting to achieve a balance of both these facets. Both cool and hot climates have their challenges, and different approaches to harvesting are required.

In the winery, the sugar undergoes fermentation into ethanol. Sometimes, (for various reasons) not all the sugar is fermented into alcohol, and thus we have residual sugar left in the wine – giving it a sweetness.

Defining ‘sweetness’ in a wine can be difficult. Ripeness of fruit flavours can be present in a wine and come across as a sweet without there being any residual sugar in the wine at all. Technically, when we say a wine is ‘sweet’ we mean there is residual sugar present, interacting with the sweet tastebuds on our tongue. Determining the difference  between this ‘fruit ripeness‘ and absolute ‘sugar sweetness’ is (unfortunately) a matter of experience. There is no substitute for drinking plenty of wine!

Acidity is registered on the sides of your tongue. Lusciously sweet wines (Sauternes for example) can often hide acidity. If you’re in doubt about the acidity of a wine, hold some of the wine in your mouth for a while. Pay attention to the sides of your tongue, and to what degree they are ‘tingling’ in response to acidity. Acid also makes you salivate, and the degree to which this occurs can also be a good indicator of acidity. All wines are acidic, so, as ever, you need to calibrate your tastebuds to what is an ‘acidic’ wine and what is low in acidity. Again – drink plenty of wine!

My personal method of examining the alcohol level in a wine is to breathe a little air over the wine as it is held in your mouth (ideally without choking and spluttering!). You’ll soon learn to detect a burning sensation at the back of your throat in response to ethanol fumes being aerated through the wine. The more swiftly that burning sensation comes, the more alcoholic a wine.

My next post will cover the wines we sampled at this week’s tasting. Good examples, I think, of all the elements of acidity, alcohol and sugar.


About James

Dr James Flewellen is a biophysicist, award-winning wine writer and educator based in London. Keep up to date with his writings and tastings at
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5 Responses to Acidity, Alcohol & Sugar

  1. Neel Burton says:

    Great tasting today. 2009 looks like a great vintage in the Rhone, with the Coudoulet de Beaucastel already standing out. Some more great tastings coming up this week… what a great time we are having! Thank you for posting.

  2. Pingback: Acidity, Alcohol & Sugar – the Wines | The Oxford Wine Blog

  3. Pingback: A selection of sweets | The Oxford Wine Blog

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