Matt Brain is a consulting winemaker and educator based in Napa Valley. With recent experience as the winemaker for Alpha Omega winery, he formerly lectured in the enology and viticulture programs at both Cal Poly San Luis Obispo and Fresno State University in California. He earned degrees in biosciences at Sam Houston State University and in winemaking at the University of California, Davis.

Winemaking is an exercise in precision and timing. In order to make the best wine possible from each vineyard block, the grapes must be harvested at the absolute ideal time depending on the style of wine and flavors desired as well as the grape chemistry. If that window is missed (and since harvest occurs annually, as you all know) producers have exactly one year to berate themselves for their mistakes, and mourn their opportunities lost.

For this reason, winemakers put a lot of pressure and demands on their vineyard managers and viticulturists to help get the fruit to the winery on time. In an area like Napa Valley, where the vast majority of vineyards are planted to one variety (cabernet sauvignon), stress and friction can be challenging. It’s no surprise that winemakers can become short-tempered under this pressure.

So what exactly does perfect harvest timing look like to a winemaker, and why is this timing so important to the production of the highest-quality wine possible? Let’s put aside the fact that pest and microbe pressure, winery capacity, availability of picking crews, heat waves, fires and logistics may force an early or late harvest (although these can be real challenges) and focus on the grapes themselves.

Let’s start with flavor, aroma and texture. If the fruit is underripe and green, a vegetal flavor and aroma will be present, and the tannins (in a red wine) will be both bitter and astringent.

Some producers really ride this line, preferring a complex, finished wine that shows some green notes along with bright, barely ripe fruit. These wines age incredibly well, gaining approachability and appeal over time, but they have become harder to find since the 1990s.

In contrast, if the fruit is picked overripe, raisin and prune characteristics can dominate the varietal and locational personality of the finished wine. While possibly appealing in the short term, these wines turn sweet and cloying quickly, and really don’t cellar well. The aroma and flavor really define a winery’s house style. Managing a precise harvest and subsequent craftsmanship of these two qualities are most important!

Grape chemistry is almost equally as important, and producers focus closely on both acidity and sugar concentration to help guide their timing of the harvest. In the category of acidity, we look at both the pH of the grape as well as the titratable acidity (TA). These two measures often correlate but are definitely unique with respect to the finished wine.

Left: Executive Editor Jim Gordon helping to sort an old-vine zinfandel field blend last month at the J. Rickards Winery in Alexander Valley, Sonoma County. | Right: Grape grower Glenn McGourty picks a viognier grape bunch at peak ripening in his Bonfiglio Vineyard in Mendocino County, California.

First, pH measures the concentration of free hydrogen ions in the solution. In the grape, pH correlates with skin softening, and when it rises above 3 the skins start to become vulnerable to mold, insects and unwanted attention from all sorts of organisms, as well as attachment of airborne smoke.

The pH level also drives ageability in wine (the lower the better) and defines the wine’s ability to repel infection by unwanted microbes, most often in conjunction with small amounts of added sulfite. In short, we desire the lowest pH possible while achieving the flavors and aromas that define the grape and region.

TA, on the other hand, refers to the juice and wine’s acids that can be titrated by a standardized base in the lab. This measure tells us how tart in the mouth the wine will be. Ideal TA values usually run in the 6-7g/L range, with values higher making a wine taste aggressively sour, often needing some sweetness for balance – think sparkling wine or German rieslings.

TA often correlates inversely with pH, but in the best soils and growing areas, TA values will be lower with excellent (low) pH, a combination that allows both balance and healthy, ageable wines.

Sugar content is the easiest to monitor during harvest, and it directly translates to the alcohol level in the finished wine. So unless you add sugar (not permitted in California but not uncommon in tough-to-ripen areas like Burgundy) or water (sometimes necessary but always results in diluting flavor), we as winemakers need to have sugar levels that will allow us to keep a resemblance to style consistency, or at least land within acceptable final alcohol ranges.

If alcohol concentration is too low, a wine can feel thin and weak in the mouth, while extremely high levels can make the wine come across as boozy and muddled, muting the taster’s ability to detect the subtle nuances we are working so hard to reveal.

And if we don’t get all of these sensory and chemistry characteristics right, the finished wine simply won’t be the winemaker’s ideal expression of the variety, vineyard site or house style.

Subsequently, we will not be able to confine our grumpy nature to harvest time. Not only will our viticulture colleagues suffer, but so may family and friends for the entire coming year, as we taste our wines through elevage and lament the perfect expression that almost was.

BRAIN ON WINEMAKING: TIMING YOUR HARVEST LIKE A PRO

– Matt Brain