Dry ice is thrown into the tank once all the must has been flushed through the hose from the crusher to the tank. Dry ice is carbon dioxide (CO2) and comes in pressurised tanks just like helium or oxygen would. In this image you can see that the dry ice is "melting", releasing CO2 and the CO2 gas is spreading over the cap. CO2 is heavier than oxygen and therefore sits on top of the must, acting as a protective layer against oxygen oxidation. The must was then left over night, so that we could relax for a delicious dinner. The following day we took a 100ml sample to Damien's lab and measured that the must had a beaume of 14.02, pH 3.88 and total acidity 6.2.
1 degree Beaume (a measure of the specific gravity of sugar in the must) ferments to roughly one degree of alcohol.
pH is a measure of the concentration of hydrogen ions in a solution and is a logarythmic scale. The greater the concentration of hydrogen ions the lower the pH. Wine makers the world over understand that a pH higher than 3.65, will leave a wine prone to bacterial and non-sugar fermenting yeast spoilage (e.g. brett). The lower the pH the higher the hue of purple in a wine and the tighter the mouthfeel. A low pH also means when sulfur is added to a finished wine, less of that sulfur can be bound to molecules in the wine, meaning that a wine will have a higher "free-sulfur" content prior to bottling. Sulfur is added to almost all finished wines prior to bottling to reduce potential oxidation and to stabilise the wine from microbes. Free-sulfur molecules are not irreversibly bound to solids in the wine. More free-sulfur means greater protection from oxidation and therefore greater longevity of freshness in your wine.
Total acidity is a measurement of the total acid concentration (g/L) in a must or wine. Acid gives a wine structure and backbone.
After looking at the lab results it was decided that a slight acid adjustment would be made to the monty must, remembering that once the ferment is finished the red wine will eventually go through malolactic acid fermentation (naturally). Here malic (apple acid) is naturally fermented to lactic (milk acid) by lactobacillus bacteria. When this occurs the total acidity of the wine drops. Malo-lactic fermentation will be discussed in greater detail when our wines head this way.
