Grape juice and the resultant wine contains quite a number of acids, the main ones being malic and tartaric.
The amount of acid in a wine is known as titratable acid (TA) and the acid strength is known as pH. Acid is an important component of wine contributing to taste (balance) as well as the chemical reactions that take place during the wine making process both natural and winemaker induced.
Malic acid is very tart and somewhat unstable in wine.
To improve the acid taste and increase the stability of wine it is prudent to convert this malic acid into the softer and more stable lactic acid, particularly in red wine.
This is done by introducing lactic acid bacteria (LAB) either as a culture or by natural means from the bacteria already present in the winery.
We use an Oenococcus oeni culture which is added to the fermenting must.
These little fellas (the white ones) get to work 'consuming' the malic acid and turning it into lactic acid and carbon dioxide. The evolution of this gas is the reason the process is called a 'fermentation'.
Improved wine stability comes about from not letting this process happen when the wine is in the bottle with obvious dire results ie. blown out corks and shattered glass.
MLF however will not take place in the presence of sulphur dioxide which is added to wine as an antioxidant and antibacterial agent. You see this as 'Preservative (220) Added' written on a wine label. This means we have to leave the wine unprotected until the MLF process is complete.
This is always a bit of a nail biting time in a simple Vin de Garage winery so this is the reason we add a culture ie. to get the process going and finished as quickly as possible.
The only sure way to detect if MLF has occurred is with a paper-chromatographic test.
In the meantime Vintage 2011 continues with the Semillon racked off the fermentation lees (dead yeast cells) and bentonite (clay used for stabilization and clarifying) residue and sulphuring. Now we just wait until all the remaining solids settle out and the wine clarifies. This may necessitate another racking or two plus sulphur additions.
The Tempranillo has gone through MLF and has been racked off the fermentation lees, sulphured and egg white added to begin the clarification process.
We are waiting for the Pinot Noir to complete MLF.
It continues to rain and rain. So far the Cabernet Sauvignon is holding up but experience has shown that a 'collapse' of bunches can occur virtually overnight eg. splitting.
So we are ready to pick at a moment's notice. It could be we are forced to make Rose' from this grape variety this year.
Only time will tell.