Brix

Brix is one of the important factors in determining harvest.

Grapes are picked when they reach the proper sugar/acid ratio for the style of wine the vintner would like to produce.  If you were to go to a vineyard in June and taste one of the small green grapes your mouth would pucker because it would be tart and acidic. 

 Return to that same vineyard-even to the same vine-in late August or September and the grapes will taste sweet.  All the months of sun have given the grape sugar as a result of photosynthesis.   

Brix is also an important factor in determining when a fermentation is finished.  Sugar is present naturally in the ripe grape.  A fermentation is finished when all the sugar has been converted into alcohol or the alcohol level has reached 15 percent, which kills off the yeast.

Brix is measured during fermentation with a hydrometer .  One degree on the hydrometer scale is equal to 1 percent brix.  The grape juice is poured into a calibrated cylinder, then the hydrometer is inserted and allowed to sink to equilibrium level, depending on the density of the solution.   Since sugar accounts for most of the increase in density of the juice above the density of water, the instrument can be calibrated to read the percentage of sugar directly on the stem.