“Don’t look down.” This is good advice when you are standing on the top rung of a ladder.
This is also the advice I was given when I first learned about crop thinning six years ago. As with many things in this industry, if you ask ten people a question you are going to get ten different answers but the above sentiment seems to hold strong across the board.
That is because dropping fruit in the vineyard is equal parts necessary and gut-wrenching. It is hard seeing all of that fruit on the ground. In this article I discuss fruit thinning with the owners of Coastal Vineyard Care Associates.
“Thinning is all about vine balance; balancing the leaf surface with the crop load. If you have a small canopy, it isn’t going to be able to evenly ripen a large crop load, so you drop fruit,” explains Jeff Newton. For Jeff, this balance is the most important thing. A big vine can ripen a big crop but a small vine can only ripen a small crop. In Jeff’s experience, the best grape quality comes from a small vine with a balanced crop load. This makes sense, but then there are the grape cultivars that are overly ambitious. “Petit Verdot, for whatever reason, is super fertile and will give us a lot of crop but not enough leaf surface area to balance that. So after fruit set, we will thin it to two clusters per shoot, which is about the average for a typical grapevine.”
This first thinning seems to be the standard in the industry. “You rarely see people thinning fruit before bloom; it is very risky,” Says Ben Merz. “You can’t know how many of the flowers will fertilize and set; you may have a wind or rain event or cool temperatures and lose most of the inflorescences, so more often you see people doing their first thinning around fruit set, either before or after, because it is much easier to evaluate the amount of shatter you will have,” he continues.
Ruben Solorzano likes to first thin fruit around set as well, generally leaving one to two bunches per shoot, “I’ll thin again about 20 days after set to avoid irrigating. If it looks like the vines need water, I’ll drop fruit.” This will help balance the crop load but also maintain a smaller, more concentrated berry. Mike Testa agrees with this timing, “It is easiest around set because you can just pinch the clusters off. It goes much faster.”
At this time you can calculate the weight of the clusters per vine which will help you calculate the tons per acre. “However, it is of my opinion that as an industry, we need to move away from using tons per acre as a measurement and instead talk about yields in terms of pounds per vine,” says Ben. “Vineyard ranches can have variable planting density. Two tons per acre is very different on a block that is planted at 500 vines per acre than on a block that is planted at 6,000 vines per acre.”
“There tends to be a different fruit thinning tolerance for grapes intended for red wines than for those intended for whites or rosés,” Ben adds. “Some producers feel that it is okay to have high yields for white wines because whites are more about the aromas, whereas reds are more focused on mouthfeel, concentration and weight; particularly tannins. Over cropped vines don’t seem to develop these characteristics as well.” The size of a berry is important as it is correlated to the skin to juice ratio. With white wine, it is all about the juice, so a heavier crop load (with larger berries) can be good in some cases. But all of the pigment, tannins, etc., live in the skins of red grapes. “Therefore, having a smaller berry means you will have a higher skin to juice ratio, and thus a more concentrated color, tannin content, and flavor.” So, we will stress a vine from fruit set to veraison because that is when you can really influence the size and weight of your clusters. Ben states that we will water more during bloom to help the canopy grow, “you have to make sure your canopy is sufficient before stressing vines.”
Thinning fruit about a month before veraison can also help open up space in an overly crowded fruit zone. “This is very important with Syrah and Grenache,” Jeff says. “The clusters of these cultivars tend to grow together and get tangled, so before berries start softening is a good time to untangle them and strategically thin.” While the berries are hard we can afford to be a little rough with them and can trim the wings (also called shoulders) of the bunches, as this is the part of the cluster that typically lags behind.
Opening up the fruit zone helps us mitigate disease pressure. Grapes packed too tightly together do not have enough airflow and are thus more likely to have issues like botrytis or powdery mildew. Botrytis, sometimes called noble rot, is generally undesirable as it can cause fermentations to stop and can lend off-aromas to the finished wine. By thinning the crop and opening up more space between bunches, we allow for increased airflow and sun exposure. “For red wine, the magic is in the skins of the grapes,” says Ben. “If your grapes aren’t getting enough sun exposure, you will lose a bit of that magic.”
“If your grapes aren’t getting enough sun exposure, you will lose a bit of that magic.”
The third major time that crop thinning will occur is around 85-95% veraison, when clusters are almost done changing color. This third crop thinning is often referred to as ‘green drop.’ “During long set periods, like this year, we see highly variable ripening periods,” comments Mike. “Some clusters didn’t set until a week after a neighboring cluster, so some bunches will lag behind others.” This is the last time you can easily see, without testing with lab equipment, the uniformity (or lack thereof) of the vines. Though this thinning is called green drop, since we are mostly dropping the green fruit that is lagging behind, in some years we have had to drop fruit that was far ahead of the rest of the bunches. “Essentially, this is the time that we are pulling out the outliers,” says Mike.
This is also the time you can weigh your clusters to compare to the weights you calculated after fruit set. Ben notes that every vintage is different. “We have seen cluster weights double from 100% veraison to harvest and we have also seen them shrink within that time period. This is mostly dictated by Mother Nature.”
Ruben and Ben agree that a final fruit thinning will occasionally be done just before harvest. This is where we will sometimes pull individual berries. “Basically, the general rule is if you wouldn’t eat it, you should drop it,” laughs Ben, “If there is damage from sun burn, disease, insects, or animals, we will go through and sort it out.”
The goal of fruit thinning is to achieve balance and to enhance the quality of the fruit. But you do not want to drop fruit unnecessarily. “You would be surprised at how much fruit is needlessly dropped,” says Jeff, shaking his head in bemusement. “As long as your crop load is balanced with the canopy, there isn’t a significant change in the quality of the grape beyond that. But we do want to satisfy the stylistic goals of our clients. If they would prefer a large crop, we can do that, if they prefer a smaller crop, we can do that too. But we always try to keep the vines in balance.”
In the end though, Mother Nature mostly dictates how big a crop is going to be. All we can do is try to achieve balance with our cultural practices and to remind ourselves, “Don’t look down.”
Heather Daenitz is a Viticulture Generalist with Coastal Vineyard Care Associates. She holds a Bachelor’s of Science in Viticulture and Enology from Oregon State University and currently resides in Orcutt, in Santa Barbara County.