Grape harvest approaching quickly
August 24, 2006
Wine grape harvest traditionally takes place in September and October in the Northern Hemisphere and in March and April in the Southern Hemisphere. In very hot climates it may take place in mid-summer. The exact time of harvest in all vineyards throughout the world depends on the ripeness of the grapes. The perfect ripeness is when there is a good balance of sugar and acid and that grape taste exactly like what that specific varietal is, meaning a merlot grape should taste like merlot and so forth. The time when the grapes are picked and then pressed and made into wine is the vintage date of that wine.The timing of the harvest is a complicated time for viticulturalist for many reasons. Like most crops, the entire vineyard does not ripen at the same time, therefore the harvest of a single vineyard may take several days. In hot weather, once a grape reaches perfect ripeness, it must be picked very quickly before the hot weather over-ripens the crop.
The traditional method of harvest has been by hand, where the harvester cuts the bunches of ripe grapes off the vine . Manual harvest insures that only ripe grapes are picked, and that there arent any twigs or leaves that will make the wine bitter. Hand-picking is employed in many European vineyards, in steep vineyards and where the wine-maker insist on undamaged, high-quality fruit for their fine wines. Mechanical harvesters are far more efficient than hand picking and are used in many large vineyards. They are especially efficient when the harvest takes place at night to avoid the harmful effect of hot weather on the grape crop. A mechanical harvester can pick from 80 to 200 tons of grapes in one eight hour shift, while an experienced harvester can pick 2 tons in a shift, which is amazing in itself.Interestingly, depending on the quality and type of grape, a ton of grapes can produce around 60 cases of 750 ml. wine.
Most grapes will stay green, whether they are red or white types, until about six weeks prior to harvest, which is about the middle of August here in California. After reaching full size the grape will change color and they will taste very sour at this point. As sugars begin to be stored in the grape they begin to become sweeter. Generally under optimum growing condition a wine grape will mature in 120 days, longer in colder years and shorter in hot seasons, which means any temperature above the mid-80s.To determine the ripeness of the grape, the vineyard manager will measure the concentration of dissolved solids present in the grape with a refractometer. Ninety percent of the dissolved solids are fermentable sugars, and obtaining this reading will give a reliable indication of the ripeness of the grapes. In the United States and Australia the Brix scale of degrees is used to measure the percentage of solids in the grape. Baume is the European scale, and Oeschsle in Germany. By measuring the amount of sugars present in the grape the harvest date can easily be predicted. These levels as well as the pH (acidity) of the grape are very important to the wine maker. Sugar levels will create the alcohol level and the sweetness of the wine. The acidity will contribute the balance and flavor of the finished wine.These measurements continue regularly prior to harvest because the levels can change dramatically depending on the weather. Warm days will allow the sugars to form and the acidity to drop appropriately. Cold temperatures close to harvest time will keep the acidity high and sugar levels low. Hot temperatures can damage the grapes by creating low acid levels, which will produce wines that are dull, or too much sugar, which will create too high of an alcohol level. Hot weather will also diminish the flavor and aroma characteristics of the grapes.The wine maker and vineyard manager must take the sugar and acid levels, as well as the true varietal flavors, into consideration for choosing the correct harvest date for the vineyard. They will sample grapes from different parts of the vineyard to determine the ripeness. The heat wave we experienced in July may have lowered the acid levels in the grapes, and depending on the variety of grape, may give us a little earlier harvest time than last years.Janice Jones Truckee resident and wine consultant. Reach her at firstname.lastname@example.org.