Everybody has heard of fermentation. Every take-away you've ever eaten has reminded you of its bilious existence.
It's that unpleasant business where the tucker you eat is broken down by micro-flora resident somewhere below last years hiatus hernia. This reaction releases quite a lot of heat, and copious amounts of gas as well as providing you with the energy needed to catch and cook your next meal.
So to, with wine. Primary fermentation, or, as it's better known, alcoholic fermentation, is the process through which the accumulated sugar in ripe grapes is converted (mostly) into alcohol and carbon dioxide. There is a direct relationship between the ripeness of the grape and the alcohol content of the wine. In a country like Australia, with its amazing sunshine, responsible for prodigious sugar levels in ripe fruit, this is cause for celebration. In fact, locally, it is illegal to add sugar to crushed grapes before or during fermentation.
Not so in France. Although the amount of chaptalisation (sugar addition) is controlled, the practice is widespread. In Burgundy, there is some suggestion that this habit is responsible for the remarkable body and mouthfeel of some not so obscure, and not so lowly priced wines. Chaptalisation certainly doesn't play second fiddle in the many lesser wines of this area.
However, while the French turn an official blind eye to sugar addition, they myopically peer down their collective noses at our habit of adding acid. Except in the very coolest areas of Australian viticulture, (eg. Orange, Ballarat, Launceston),it is common practice to toss a bucket of tartaric acid into the must at the crusher to raise the acid level in the finished wine. While a moderate addition may be as low as 1 gram per litre of juice, much more is needed when grapes are overripe and are showing high pH levels. Adding acid helps produce better balance in the wine, and a low pH helps to stabilise the brew once primary fermentation is completed.
There's an awful pong creeping out of our barrels at present. It's a strange sort of stale beer and mushroom smell which would almost be enough to make even a Foster's drinker pause between gulps. It happens at about this time every year. In fact I make it happen. It is a little recognised but useful secondary fermentation called the malo lactic fermentation. Many a home bottler who has uncorked a robust sparkling burgundy, when what was put down could loosely be called 'claret', is unhappy witness to the might of the 'malo'!
Grapes, particularly from cooler areas, have a fairly high malic acid content. This acid not only adds to the tartness of the finished wine, it is also an unstable acid, subject to attack and breakdown by malic 'eating' bacteria. If a wine is bottled containing malic acid, unless it is processed under completely sterile conditions, there is a good chance that malolactic bacteria or, even worse, acetobacter, will present the wine waiter or host with an indelicate choice. In fact, the pong can be so pungent, and the fizz so effervescent, that the description 'off' is entirely appropriate. Some fast talking or a handy sink is usually the order of the day.
Where does it come from, this malolactic bacteria? Well, it appears. Like most things vinicultural, malolactic bacteria are a natural part of life. Like hares and mildew, bearded dragons and lightning fast brown snakes in the aviary, when there is a food source, they are about, whether you want them there or not. In older, established wine regions, the population of yeasts in the vineyard and winery make inoculation for both fermentation and malic conversion unnecessary. In newer regions like the Central Ranges of N.S.W, the practice is to seed ferments with selected strains of pure cultures to help this process.
When is it done? The best time to encourage a clean malo in wines high in malic acid is to introduce a selected culture of malolactic bacteriasoon after the peak of the ferment so that you can have some control over not only the strain of bacteria dominating the secondary ferment, but also the progress of its development. A check is kept on the course of the reaction until all of the malic acid is removed and the wine can safely be bottled. What usually happens to the wine is that the aroma, (which is primarily a reflection of the variety of fruit used) becomes less varietal and more vinous. That is, the wine takes on a more complex character on the nose and loses some of the overtly fruity characteristics that typify a new wine. It will also taste less acidic and more well balanced, all of which contributes to a better beverage for you and me to enjoy. And that's what good winemaking is all about.