Walk into any cellar in the Loire valley during harvest time and the chances are you’ll see wooden barrels with lots of chalk scribbles on the side. So what are they and what do they mean?
Wine is the result of alcoholic fermentation. The sugar in the grape juice is eaten by the yeasts and transformed into alcohol and CO2 (which is allowed to escape for still wines and trapped in the bottle for sparkling wines).
Wines are often fermented in 400L oak barrels. The juice is transferred to them soon after pressing and there it stays until the fermentation is over.
So how do you know when it’s over?
Well, you measure the density of sugar in the juice using a hydrometer. As the alcohol increases and the sugar decreases, the density changes and that’s what written on the end of the barrels.
A sealed glass tube with a weighted bulb at one end is used to measure the density of juice, fermenting wine and completed wine in relation to pure water. This ratio is called specific gravity.
What you’ll see on the barrel is a list of dates and then beside them, the result of the measurment taken on that day.
Dry wines measure around 0,990 specific gravity so you may see 990 or on this barrel – 994 on the 21/12/2020.
The figures chalked on the barrel show measurements taken near the beginning of fermentation and then you see the density drop over time. It gives the winemaker a good idea of how fast the fermentation is going and how much sugar is left in the fermenting wine.
