Harvest (wine) of wine, winemakers would use the sugar and acid levels of the grape as a guide in determining ripeness. Early winemakers tasted the grapes to gauge ripeness. Modern winemakers use a refractometer to measure high sugar levels and °Brix or titration tests (using an indicator such as phenolphthalein) to determine the titratable acidity within the grape. In recent times there has been more of an emphasis on the "physiological" ripeness of the grape, usually in the form of tannins and other phenolics. Currently, tasting is the only way to measure tannin ripeness, which can take experience and skill to do
Phenolic content in wine . Low molecular weight polyphenols, as well as elagitannins, are susceptible to be extracted from cork stoppers into the wine. The identified polyphenols are gallic, protocatechuic, vanillic, caffeic, ferulic, and ellagic acids; protocatechuic, vanillic, coniferyl, and sinapic aldehydes; the coumarins aesculetin and scopoletin; the ellagitannins are roburins A and E, grandinin, vescalagin and castalagin. Guaiacol is one of the molecules responsible for the cork taint wine fault. Flash release is a technique used in wine pressing. The technique allows for a better extraction of phenolic compounds. The exposure of wine to oxygen in limited quantities affects phenolic content. Depending on