Deep Dive on Acidity

Posted on February 10, 2009

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Wine Grapes

The whole Saunders family is inflicted with some nasty virus, so my sniffer is broke this week.  I have a riesling on standby for TNs as soon as my sinuses clear.  Until then, I thought I would dive into one of the big mysterious elements of wine structure for me: Acidity.  I often hear it associated with “freshness” and “liveliness” or “refreshing qualities” – that doesn’t work so well for me.  I want to get into it a little more, understand it technically.

Grapes have naturally occurring acids – the three important fixed acids are malic, tartaric and citric.  Other acids are present – lactic, succinic, butyric and acetic acid.  I’m working under the 80/20 rule so I’m not getting into the others.  Of note is acetic though – it’s a volatile acid found in vinegar.  You’ll see the wine fault VA referred to – this is the overabundance of acetic acid.

Tartaric acid is a relatively rare organic acid.  The quantity of tartaric acid in a grape is pretty much static from flowering to harvest.  It doesn’t get metabolized through normal respiration processes.  Certain varietals naturally produce berries with higher levels of tartaric acid.  This particular acid plays a key role in wine making – keeps the fermenting must at a pH level low enough to keep out nasty bacterias, and it helps preserve the wine after fermentation.  It also helps stabilize the colours. Tartaric acid provides tartness to wines – it’s actually used to add “sour” flavour to many food products!

Malic acid is found in many plants and berries.  Most folks associate malic acid with green apples because it really gives you that flavour profile.  Concentrations of malic acid are also varietal dependent, but it actively participates in metabolic processes within the grapevine.  Just before veraison (grapes start to turn colour) the concentration of malic acid in grapes reaches its peak.  As respiration continues, and the grapes continue to ripen and malic acid is metabolized.  In cooler climates, nighttime temperatures are low enough to slow respiration and malic acid is preserved in the grapes. In warmer areas, respiration continues to consume it more quickly, and can metabolize most of the acid by harvest.

Malolactic fermentation is used to convert malic acid to lactic acid.  It involves inoculating the wine post alcoholic fermentation with a specific bacteria.  The bacteria  will consume malic acid and produce lactic acid.  While malic acid is responsible for that green apple tart taste, lactic acid is much rounder, richer – it is the acid in milk!  Diacetyl is produced as a result of this chemical process, and is responsible for a buttery kind of smell.  I’ve most often experienced oaked chardonnays that have gone through MLF – most recently Hidden Bench’s Chardonnays – and the best examples of the process are rich, buttery, luxurious wines.

Citric acid is present in very small quantities in grapes and rarely makes it to the wineglass.

What does all of this mean?  This leads up to pouring a nice glass of wine.  Can you smell acidity?  VA is a wine fault you can smell – normal acidity some folks say they can get, I don’t know if I ever have.  Drinking a wine, you get that tart/sour kind of feel around the front of your tongue.  It should balance with the fruit flavours, tannins and alcohol in the wine.  A wine with not enough acidity is often called “flabby” – easy to find in some cheap warm climate chardonnays. You’ll drink it and get a lot of fruit but think something is missing.  Wines with too much acidity are sharp – I’ve had some sauv blancs that are over the top acidic, and a really young bandol – in both cases it was almost like drinking a carbonated beverage it they were so acidic.  Your tongue will curl, and may seem bitter depending on the other components in the wine.

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