Once in the fermentation bins the must (freshly crushed juice with or without skins)   is analyzed chemically to determine various parameters: pH-rough measurement of acidity of the juice. TA-exact measurement of the titratible acids. Specific Gravity-measurement of the sugar present.

We prefer to rely on the natural condition of the juice and not manipulate it,  but occasionally we find the numbers are incompatible with the style of wine we hope to make,   and need to intervene. For instance,  our estate-grown grapes are often lacking in enough residual sugars to make a wine with a reasonable % of alcohol,   so some cane sugar might be supplemented.  We sometimes find the pH is too high to make the crisp,   acidic,  Alsatian-style whites we favor,   and we might add tartaric acid to increase the acidity.