Watson: Pray tell Sherlock – the answer to what?
Sherlock: Simple, Mr. Watson, the answer to malo-lactic fermentation.
Watson: Malo what?
Sherlock: You see, Mr. Watson, there are many types of fermentation. The best known is the fermentation of grape juice or other fruit with yeast added to create wine. The yeast transforms the sugar into alcohol and voila! – you have wine.
Then there is the fermentation of a wine/alcohol base to produce vinegar. This little beast of a yeast called aceto-bacter feeds on alcohol. Methinks it must get tipsy. For cooking, cleaning etc you get pure vinegar or acetic acid, red and white wine vinegar, even mead vinegar. Not too great for the home winemaker as a bottle of wine is worth more than a bottle of vinegar.
Furthermore dear Watson, nature provides dozens of types of yeasts in the wild, especially in the summer and early fall. When fruit fall to the ground, the hungry air born yeasts will feed on it. The sugar in the fruit will ferment, CO2 will bloat the fruit and it will expand, giving the birds a lovely meal! This may explain birds flying into windows…
Also, there is bread. Think about it for a moment. Yeast is added to bread dough and it ferments producing CO2 – which causes the dough to rise.
Watson: But Sherlock, what is your point?
Sherlock: Oh sorry chap, by all means. Malolactic fermentation is just another type of fermentation. Just a lot less common than most others.
Depending on the weather, soil and humidity – among other factors, some grapes will contain more malic acid than usual. But wine has the ability to adjust itself. This type of fermentation occurs during the initial fermentation and sometimes continues to take place after the wine has been bottled several months later. Commercial wineries, in order to avoid this, will cold chill the wine at 2 degrees celcius in order to accelerate the process. This can occure in all wines.
But for the home winemaker, things are a bit less simple. The process has 3 stages.
1) The wine will turn cloudy – especially visible in whites.
2) The cloudy wine will coalesce and form flakes.
3) The flakes will join and form little granules that look like grains of salt.
These salt granules are called "diamonds of wine" once they settle. Home winemakers who first experience this process panic. They go 'tally-ho' with the wine and think they have failed.
Wrong move. The wine is perfectly good and – better yet, has balanced itself as part of the aging process. For good measure, the wine should be left open for a bit to let any gas leave before sipping. That's because the gas produced by this fermentation (not CO2) is quite foul. So Watson, email this to Moonshiners – the explanation is a diamond.