The quality of a wine derives from the grape. By the time we’ve planted the grape vines, it’s wine harvest season, which in Italy goes from late August to October or even up to November, for the so-called “late harvest”. In fact, in late summer the grapes are ripe enough and contain a good balance of sugar (which increases over time) and acid (which tends to decrease). At this stage we can proceed with the grape crushing and winemaking.
But, how do we know when the grapes have reach the desired quality? First of all, we will have to collect samples, picking bunches of grapes from different parts of the vineyard. We will then need to press them with a small press, to obtain 250ml of juice and with the hydrometer, measure their gravity (density) to detect the content of alcohol of the wine after fermentation. In Italy, we use the Saccharimeter Babo thermometer, which shows 10 sugar grams for every 1000 grams of liquid. After writing down its Babo degrees, subtract 4 from this number and multiply it by 0.85 (for white wines) or 0.80 (for red wines).
Pour the liquid in a flap at the end of the refractometer. Count 30 seconds and put the refractometer against a source of light (hence the name). To see the results you will need to look through the lens like with a microscope and calibrate the focus like in photography. Repeat the tests three or five times, until you reach a good balance between sugar and acid, 10-11 alcohol degrees percentage for whites and 12 to 13 for the red. The more grapes ripen, the higher the sugar content. Indeed all dessert wines come from “late harvesting”.
At this stage we can then pick the grapes. To avoid the grapes being crushed and squashing each other, it is preferable not to use a huge basket (max 20 kg). It’s also very important to keep the grape skin intact. More to follow in the next article.