The discussion of acid in wine can be a caustic topic amongst wine makers and, in particular, wine judges.
It is bandied around by those who are keen to espouse their wisdom on willing subjects. Comments on its levels and effects on the wine immediately elevate you into another level of “wine boffin”.
Acid and fruit sugars are a little bit like the yin and yang of Asian spirituality; one can’t exist without the other unless in the right harmonious balance. Too much acid, and you may as well have some lemon sherbet.
The most common fixed acids found in grapes are tartaric, malic and lactic, with acetic being known as volatile acid.
Heading back to chemistry 101, the pH is the measure of free acid, and the lower the number, the more free hydrogen ions are swimming around.
Sparkling wines range from pH 3-3.5, whites 3.2-3.6, and reds 3.5-3.7.
Where fruit ripens easily, such as in Australia, acid can be added to balance sugar levels. But in cool climates like France, you can add sugar, but not acid.
Acid is usually added at fermentation, but it can be mixed in at any stage.
In addition to balancing sugar, the other important job of acid is to help keep unwanted bacteria out, and to act as a long-term preservative.
An important bacterial process is the conversion of malic acid, which is tart like green apples, to a less hydrogenous state in the form of lactic acid.
Almost all red wine go through this process, while the only white to undergo this process is Chardonnay.
The wine maker can vary how much “zing” he wants his wine to have by cooling the process, or using some commercial techniques to stop the bacterial process.
One of the world’s great grapes that has lost favour, particularly in Australia, is Riesling. Acid levels are the backbone of this wine, and indicate its ability to cellar well.
Originally grown in Germany in less than ideal conditions, such as cool temperatures, slate and rocky soil with mountain goat terrain, Riesling is a magical wine.
Picked early, with low sugar and high acid, these drier styles will age for many years. They will display early floral and grassy notes that later develop hints of honey, nuts and kerosene-like nuances.
They also have low alcohol contents of 7 to 12 per cent. When left to ripen a little longer, high residual sugars are ethereally balanced by the acid backbone.
The super sweet dessert-style Riesling is achieved by over-ripening and the reduction of water by a fungus known as Botrytis, or by freezing, known as ice wine.
Australian Rieslings are the best value wine in the world. Spend $20 to $30, and you will get a wine that is a pure expression of the land and climate it comes from, with minimal wine maker influence.
It is a wine that will either drink well immediately with Thai grilled scallops or, as it ages, it will morph into an elegant, eclectic wine.
Jancis Robinson MW, a leading wine writer, has Riesling tattooed on her right forearm. I don’t think she has any piercings or rides a Harley though. Riesling is cool by her standards.
Clare Valley wines have a lime zest and full mouth flavour, while the other major Riesling region is Eden Valley, which has wines that have more lemon notes and sharper acid structures.
Tasmania makes cracking cool climate Riesling.
Dr Loosen Riesling 2012 ($22) – from Mosel, a large producer. Nice floral, lime and mineral notes. Balanced mouth sweetness with acid. Sashimi scallops match.
Valli 2012 Central Otago ($25) – Honeysuckle notes with limes. It feels sweet in the mouth, but with a nice dry finish. One of the few NZ wines with low residual sugars. Have with Brie or soft blue on toasted rye.
Henscke Peggies Hill 2013 Eden Valley ($18) – super citrus lemon/lime florals with a short sharp burst of fruit, followed by a lingering acid backbone. Battered fish and chips.
Leo Buring 2013 Clare Valley ($16) – The best value wine in Australia. Floral honeysuckle notes with limes. Gentle fruit expression with a crescendo of well-balanced acid.
Leo Buring 1996 Clare Valley (about $9) – an 18-year-old wine with a deep golden colour, honeysuckle aromas dancing around wafts of minerality and still but lively lime notes. Generous softened fruit characteristics, but still lively acids. Goats chees soufflé`. I couldn’t resist the challenge of old versus new!