The 2020 grape harvest is upon us, and the first tractors pulling their trailers are already causing traffic jams in the villages. Most vignerons are still holding out, waiting for the optimal time to pick their Muscat, Sauvignon or Chardonnay, which are three of the earliest varieties to be harvested. But how do the wine growers know when is the best time to harvest? Is it always at the same time? The answer to that last question is a rersounding NO! In fact with climate change, over the last 20 years we have seen picking times swing by up to three weeks! How then can we decide when is the optimal time to harvest? There are three types of maturity that can be tested and followed: Technological Maturity; Phenolic Maturity and Aromatic Maturity. Technological Maturity. Harvesting too early might mean not enough sugar and too much acidity. Too late the inverse. The most frequently used method for getting a quick idea of maturity is to use a refractometer. This device can be used to detect the level of dissolved sugar in the juice of grapes which will have been picked at random around a particular vineyard. When the level of sugar is known, a calculation can be made to work out the potential alcohol level after the fermentation. A vigneron told me yesterday thet the Syrah was at 12.4° that morning, which is a relatively high value so early in the season in that area. However, they will wait until that reading is at least 13.5° before harvesting. As the sugar levels increase, the levels of acidity (particularly malic acid) decrease. When the levels of sugar and acidity are optimal, Technological Maturity has been reached. Phenolic Maturity. Wine contains many compounds which are referred to as polyphenols. Two in particular are studied closely at harvest time: tannins and anthocyanins. Tannins as we know are what can give an astringency to wine, in particular reds. Determining the optimal time to harvest based on the maturity of the tannins depends upon the style of wine that is being made. In the Médoc region of Bordeaux, the maturity of the tannins in a Cabernet Sauvignon with aging potential will not be the same as that in a Vin de Pays Cabernet in the Languedoc which is destined to be ready to drink within the year. Climate has a role in this but the Bordeaux style requires more tannins. Anthocyanins are compounds which give colour to wine and are particularly important for reds. The maximum extractable amount can be tested for and is another factor towards deciding when to harvest. Aromatic Maturity: As the grape ripens it develops aromas and flavours, going from green and tart to ripe fruit. If left too long and in hotter climates, this aromatic profile can become jaded, and I often taste reds from this region which lack complex aromas and are simply jammy fruit. Deciding on the aromatic maturity is done simply by tasting the grapes regularly during the last three or four weeks of maturation. As you can see, the chances of everything coming together at the same time are slim, but it can happen. But then there are other factors which can influence the end product: levels of nitrogen compounds for example can influence the performance of the yeasts during the fermentation; potassium levels can have an impact on the acidic stability of the wine. It's amazing that any good wine gets made at all when all of these factors are taken into account and I have hardly scratched the surface here! Despite issues with mildew which have persisted for many vignerons this season, this year's harvest looks promising AT THE MOMENT. Fingers crossed that some fine wines will be produced and we can finally say that something good came out of 2020!