Winemaking begins in the vineyard, long before the first grape is crushed. The single most important decision at this stage is choosing the exact day to harvest. Pick too early, and the wine might be thin and sour. Pick too late, and it could be overly alcoholic and flat. It's a delicate balancing act between three key factors: sugar, acidity, and tannins.

As grapes ripen on the vine, the sun's energy fuels photosynthesis, creating sugar. Winemakers measure this sugar content in units called Brix. One degree Brix ($1^\text{oBx}$) is equal to 1 gram of sucrose in 100 grams of solution. This measurement is crucial because yeast will later convert these sugars into alcohol during fermentation. The target Brix level varies depending on the desired style of wine, but it’s a primary indicator that harvest is approaching.

While sugar levels rise, acidity naturally decreases. The main acids in grapes are tartaric and malic acid, which give wine its crispness and structure. If the acidity drops too low, the resulting wine will taste flabby and won't age well. The goal is to find the sweet spot where the sugar is high enough for the desired alcohol level, but the acidity is still vibrant enough to provide balance.