Harvest truly is a magical time. It’s the culmination of a year in the vineyard. The world recedes to the end of a long tunnel, as all daily obligations are temporarily relieved, allowing pure, crystalline focus on the task at hand. This is true in all forms of agriculture, but particularly so in wine. For us, harvest is both the completion of our farming year and the beginning of our winemaking cycle, and it provides relief from the distractions of the wine business—the constant, daily interruptions that enrich our lives but can be overwhelming without a break. During harvest there are no sales calls, no tastings, fewer emails, no business meetings—only the daily struggle to make the right decisions and to somehow logistically pull those decisions off. What incredible pressure and excitement this creates! Everything hinges on this one thing: the harvest.
The most fundamental decision of harvest, the thing that sets everything in motion, is timing: when do I pick the grapes? This is the winemaker’s prerogative. In California and in other industrialized winemaking regions around the world, the winemaker and the grape-grower are usually two different people, and in almost all cases the winemaker is the one who decides when to pick the fruit. The grower (who could be a farmer, a vineyard manager, or a viticulturalist) has tended the grapes all year, either with input from the winemaker or on his/her own, but the winemaker assumes responsibility for this pivotal decision—because the timing of harvest is fundamental to determining wine style. The grower then organizes the people and the equipment to make the harvest happen and delivers the fruit.
Choosing when to pick is a personal decision, and one that causes a huge amount of stress and anxiety on the part of the winemaker. Winemakers can get downright strange during this time; it’s definitely one of those times when a person’s true colors come out. The whole vintage is riding on not screwing it up! Sometimes compromises have to be made due to shortages in labor availability on the part of the grower, or tank space on the part of the winery. (Of all the reasons to botch a vintage, these are among the stupidest and most frustrating for all involved, but sometimes it just can’t be helped.) Other times weather forces your hand—but you can’t blame the weather for poor planning, and watching the forecast with an eagle eye is part of the job too. In addition to following the National Weather Service, we subscribe to two different paid forecast services. If the grapes are close, and a rain or heat event is coming, it might be wiser to pick now instead of letting the fruit ride through that weather. Sustained warm weather, especially at night, means that ripening will happen quickly, so we anticipate big changes from day to day. Conversely, cooler weather might stall things out. Morning dew can lower sugar levels, while low humidity can cause sugar to skyrocket. Weather plays a huge role.
While unanticipated logistical challenges and changing weather can really induce stress during harvest, the fruit itself tends to go through fairly consistent stages as it ripens. The three main milestones of the growing season are bloom, seed-hardening (lag phase), and veraison. Tannins develop early, between bloom and veraison. While lots of things influence tannin development, the biggest factors are probably water stress, vine vigor, and (to a certain degree) sunlight. At veraison, the vine starts to produce anthocyanins in the fruit as a response to the movement of sugar into the berry. Pyrazines, which are created in the fruit before veraison, start to degrade as the fruit ripens, and other flavors start to be developed. It is important to note that the only things really moving through the vine into the fruit are sugar, potassium and some other minerals, and hormones—all of the color, tannin, and flavors are manufactured inside the grape berry itself.
As we move into the harvest window, all the anthocyanins and tannins are already present, but a bunch of key things are still happening: sugar is still moving into the berries, increasing potential alcohol; potassium is still moving into the berries, reducing total acidity; malic acid content is dropping as the berries use it as a source of energy; tannins and anthocyanins are combining into larger molecules called polymeric pigments, softening the astringency of the future wine and stabilizing the color; pyrazines are degrading, causing the fruit to taste less herbal or vegetal; fruity compounds are being created, and the types of fruit compounds are changing—the red fruits are giving way to black fruits, and eventually to cooked fruit and jam. Each of these ripening parameters is a moving target, and it is by detecting and predicting them that the winemaker dictates wine style through that all-important decision, the timing of harvest.
The most basic parameter to help determine the harvest date is Brix, a measure of dissolved soluble solids in the juice. Brix measurement does a pretty good job of predicting the final alcohol level of the finished wine. Our whole industry tends to measure degrees of Brix throughout the ripening process, so it provides a lot of indirect information about the grapes. We can gauge speed of ripening, both predicting where it is going and getting a sense of the current condition and balance of the vines. And it gives an estimate of general wine character; for example, Cabernet Franc harvested at 22° Brix will probably make very different wine than Cabernet Franc at 26° Brix—most likely, one wine will be light and green, and the other wine rich and black. Brix can be tricky, because it measures all soluble solids, not just sugars, so it is not completely accurate, but it provides a great general guide. And, once you buy a refractometer, it’s a free test. In the winery we usually test for glucose/fructose to get a more accurate gauge of potential alcohol, but that test is expensive. Brix provides a fine method to regularly monitor ripening, it just won’t pinpoint the final alcohol content with 100% accuracy.
The general rule of thumb is that you multiply Brix by somewhere between 0.56 and 0.61 to anticipate the final alcohol of the wine. So 24.5° Brix (x0.58) would result in 14.2% alcohol by volume. But it is just an estimate: factors like different sites, varieties, yeast strains, tank types, and fermentation regimes all impact the exact alcohol conversion.
Most winemakers monitor the change in pH and TA. In general, as the fruit ripens, pH goes up and TA goes down. This is due to a combination of malic acid respiration by the berries and tartaric acid buffering by potassium. (Potassium has an affinity for tartaric acid, making potassium bitratrate, an insoluble salt—the exact same crystals, or “titrates,” you see in a bottle of wine.) pH and TA will shift some more during fermentation, especially in reds, as more potassium leaches out of the skins; nonetheless, testing the fresh-squeezed fruit juice will give a very good idea of what is happening with ripening and what ballpark one can expect with wine acidity.
Malic acid itself is a nice data point to look at to see how much fuel is left in the grapes. High malic suggests that ripening is not complete, while very low malic might cause one to wonder if the berries are as ripe as they are going to get, regardless of whether the Brix has come up enough or not. A high malic acid figure might be something over 3 or 4 g/l, while a low number might be 1 g/l or below.
Some winemakers actually test the fruit for the phenolics. They send clusters to a lab that grinds up the whole berries or the skins and lets you know how much of the tannin content has polymerized with the anthocyanins to form polymeric pigments. This type of analysis tends to be done by the “long hang-time” school of winemakers, who are looking for concentrated, supple wines, and they are willing to sacrifice fresher red-fruit aromas in the search for plusher texture.
There are reams of data available, but at the end of the day our senses are still the most important tool for determining harvest timing. Most winemakers visually inspect the vineyard regularly as harvest is approaching, and they taste the fruit as much as possible. The condition of the leaves says a lot. Are they bright green and crisp, or starting to yellow and soft? Are the leaves starting to fall off? When you taste the fruit, is it softening or still hard and crunchy? Does it feel smooth or rough? Is some color bleeding out of the connection to the stem? Do the little filaments that extend from the stem into the berry pull out cleanly, or are they stained purple? Do the seeds separate cleanly from the pulp? Are they browning? Does the skin stain one’s fingers purple? Are birds starting to eat the berries? Are the skins chalky or silky? Is there a bell pepper aftertaste? Are some berries starting to fall off? Can you smell fruity aromas walking down the rows?
When the decision to harvest has been made it falls on the grower to get the fruit picked. At Matthiasson Wines the grower and the winemaker are the same person—me—but usually the winemaker has to communicate far enough in advance with the grower to get the pick scheduled. One person can pick one to two tons per day, depending on the size of the clusters and the health of the vineyard. Most harvest crews have eight people picking four-row swaths, one tractor driver, and two people picking out leaves and bad fruit from the bins. In California it is customary for the workers to be paid by how much fruit they pick, not by the hour. This lets them earn more per hour than they normally would as long as they work really fast. Ideally they get a full day’s wages in a few hours, and the fruit is picked and delivered in the morning, when it is cool, giving the winery the rest of the day for processing. When harvest is in full swing there are days when the workers have to start at night and put in long hours, which is physically brutal, but they are able to save money for the winter slowdown. Access to labor is always a challenge.
Mechanical harvesting is the norm in the interior valleys where the price of fruit is too low to justify harvesting by hand—there just isn’t enough labor in the state to hand-harvest everything. Mechanical harvesting requires huge, expensive tractors to straddle the vine rows, beating the vines to literally shake off the fruit. If the machines are set up well it can be a perfectly fine practice for quality red fruit—red fruit can generally handle some oxygen exposure—but white fruit can get excessively oxidized and tannic from the juice-skin contact (unless some oxygen exposure and skin contact is part of the desired wine style). Things are changing fast with mechanical harvesting, and there are some new high-tech harvesters with on-board sorting capabilities. There have also been great strides in developing harvesters that are much more clean (fewer leaves, stems, and sticks) and gentle (more whole, unruptured berries).
Some growers in the high-end coastal areas have started harvesting mechanically to save money and avoid the harvest labor crunch, but most premium California regions continue to rely on harvesting by hand. In many North Coast areas, it is just not possible to use a machine—many vineyards are too small, or they don’t have large enough turnaround areas for the big equipment, or they have cross arms or other trellis configuration issues that prevent mechanical harvesting.
A big trend that has developed over the past decade or so is night-harvesting. Mechanical harvesting has always taken place primarily at night to minimize oxidation by picking the fruit as cold as possible. Hand-harvesting, though, has traditionally commenced at first light in the morning. Makes sense—the fruit is picked as early as you are able, yet you can see what you’re doing. Lately, however, it has become more common for hand-harvesting to happen at night as well. The growers pull huge lights behind an extra tractor and the entire harvest happens between midnight and 8:00 am. This captures the fruit at its coldest point and gives the winery the entire day for processing. More and more wineries are sorting at the winery these days, so the time it takes to crush the fruit and fill a tank has slowed way down, leading winemakers to request fruit delivery earlier and earlier in the day.
The best day of harvest is always the first day—it is so exciting and pleasurable to get started picking the fruit; the second-best day is always the last, when we are finally finished. Plenty of beer is consumed on the first day, and plenty more tequila on that last day! All year we look forward to harvest starting; after it starts we look forward even more to it ending. The rhythms of the year are one of the pleasures of viticulture, and harvest is the crescendo of the annual cycle.
Christopher John, the fruit makes malic acid right up until veraison or so. They manufacture it between fruit and veraison, but mostly during the pre-veraison development period. I have no idea what the levels are at that time, I've never tested the fruit before veraison, but I'd think at least 6 g/l, maybe even a bit higher.
Thank you Steve for the great article. One thing I always wondered is how the grapes create malic acid. Is the level at its highest right at fruit set or does the vine continue to build malic acid up until veraison? Would the vine have like 6 g/l of Malic acid at its highest amount? Thanks.
Always love your articles! Thanks for sharing.
Fantastic insight. We often overlook or even forget the hard work it takes to grow, tend and harvest grapes before seeing the final product. Thank you.
Wonderful post. You don't often get an overview of the actually picking process. Beautiful.