Ok so yesterday we talked of brix. Today we talk of acid and pH. Brix, acid and pH are the three things you measure to ensure you pick no grape before it's time.
In his book, From Vines to Wines, Jeff Cox says, "Acids give crispness, brightness and thirst-quenching qualities to wines and are essential components of the balance in a fine wine."
Grapes contain two major types of acid - malic and tartaric. Together they are referred to as total acid or tetratable acid. Acid-testing kits may be purchased form home winemaking supply stores. The optimum level for acid is from 5 to 9 grams per litre of juice. To determine tetratable acidity the grape juice is neutralized with an alkaline solution and the point of neutralization identified.
Hydrogen ion potential or pH refers to the strength of the acidity in grapes. pH is a measure of how many hydrogen ions are combined as acids versus how many are free floating. The more free floating hydrogen ions there are, the lower the pH and the more tart the juice tastes. A portable pH pen can be used to assess grape ripeness.
When sugar comes closest to its ideal for a given grape variety at the same time that the acid comes closest to the ideal, grapes are ready to harvest. Ripe grapes will pull away from the stem easily while unripe grapes will not. Grape berries soften as they ripen, the skin of fully ripe grapes collapses easily when bitten into and the pulp is thick, but not watery. Fully mature grapes have brown seeds. If the seeds are beige or tan in color but not brown, the grapes are not quite ripe. And definitely not if you see green seeds.
Remember imbibe and enjoy!
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