lot of cellulose, insoluble pectin and proteins, and organic acids: citric, malic, and tartaric acids. The skin of the Sauvignon blanc B grape has a pH of about 4.15. It also contains between 2 and 3% tannins. The flesh of the grape is the most important part – it is between 75 and 85% of the weight of the grape. It consists of large polygonal cells which are very thin-walled. With a low pressure the cells leak their contents: the wort. The flesh of the grape contains mainly water. The organic components are fermentable sugars (between 170-230 grams for a dry wine and between 200 and 300 grams per litre or even more for Fortified wines) and organic acids, especially malic acid and tartaric acid. Acids occur in larger amounts in the centre of the berry while the sugars are in greater proportion at the periphery. This heterogeneity in the distribution of sugars, acids, and inorganic compounds in the berry is used during pressing, especially in Champagne pressing. This process separates them as it happens and uses them to measure the progress of the "vintage", the first and second tailles, and finally the rebêches of insufficient quality to be made into AOC wine. The flesh is the major element of the wine, as it is the part that contains the highest proportion of liquid. The flavours are much less present than in the skin. The wort In the case of white winemaking the wort is simply the grape juice from the pressing of grape berries. The sugars Sugars are carbohydrates derived from photosynthesis. The sucrose is made in the leaves and flows into the plant where it is broken down into glucose and fructose and accumulates in the berry where it is a characteristic of the maturation of the grapes. Many different sugars coexist: the most common are glucose and fructose which will be consumed by anaerobic yeast to convert it to alcohol during fermentation. They are in substantially equal amounts. To verify the completion of the fermentation they can be quantified by chemical assay (glucose and fructose are "reducing" sugars that react with an alkaline copper solution called Fehling's solution), an enzymatic method, or by infrared spectroscopy. Other sugars are not fermentable at all. After consumption by the yeast, the ratio of non-fermentable sugars (the ones that are not consumed by yeast: arabinose and xylose) is between 0.5 and