Harvest By The Numbers - The Science Behind It All


Ever wonder how winemakers decide when to give their fruit a little more hang time on the vine, or when to pick it promptly? Crafting a well-balanced wine relies on proper fruit maturity, and the choice of when to harvest the crop carries as much weight as any other decision in the process. Picking too early results in wine with higher acids and palpable tannins. This can be necessary if excessive heat or rain threatens the clusters. Conversely, picking too late can end with raisins- best left to Port makers.

As our 2018 harvest draws near, we’ve been busy testing berry samples in our lab to gauge how our fruit is seasoning and determine when we might pick it. Let’s take a look at the 3 key markers we test for, and how they ultimately influence Thérèse and Dan Martin’s approach to crafting beautiful wine that reflects its vintage.


Let’s start with Brix. This is a measure of sugar in the berries, and it’s at the heart of the winemaking process. Sugar ferments into alcohol, working in conjunction with acids to balance the wine and allow it to age. Measuring brix is straightforward: we utilize refractometers in the field and hydrometers in the lab that give us an instant reading. While each varietal has its own ‘sweet spot’, most dry red wines contain 23 to 26 Brix when harvested.


pH is another crucial marker that tells us the relative acidity of the juice compared to the must (all other compounds in it). Wine is acidic, and its levels fall below the neutral 7 pH of water. pH contributes to a wine’s ageability and stability in the barrel; if it gets too high, the wine can oxidize and microbes can spoil it. We use a sophisticated little instrument called a pH meter to measure it. Depending on varietal, we look for levels in the range of 3.1 to 3.4 for whites, and 3.4 to 3.6 for reds. The pH will increase as the fruit hangs and sugar goes up while acid drops. It will also change greatly from beginning to end of fermentation, increasing after malolactic fermentation.


Last but not least, TA (titratable acidity) is a measure of the total acids (primarily tartaric, malic and citric) in the juice. TA and pH have an inverse relationship to one another; the higher the TA, the lower the pH and vice versa. Both are necessary to create a stable wine and inhibit bacterial growth. Too few acids and a wine will feel flabby and dull, but too many and you’ll get an intensely tart flavor. TA testing looks a lot like a chemistry class: we slowly add a base to our juice, swirling them together until we see the indicator (change of color). With a quick math formula, we can figure out our TA based on how much liquid was used to reach the indicator.

Last week we brought in our first samples: Merlot from Victoria Denice Vineyard and Pinot Noir from R*E*D Vineyard. Here's assistant winemaker David Dockendorf discussing the numbers.