Shatter, sunburn, and millerandage: the challenge of estimating crops in a year like 2023

Exactly one year ago we started the 2022 harvest with four tons of Viognier off the estate. Not this year. Here we're still in such an early stage of veraison that there's a lot more green than red out there in the vineyard. On a positive note, the more time that the grapes have on the vines, all other things being equal, the more complexity of flavors. The flip side to that is that the same things that caused us to be behind can potentially impact our yields. I'll dive into the three main issues we're seeing in this blog, and share some conclusions, as best we can tell at this point, at the end. 

Shatter

When grapevines flower, you hope for benign weather: warm (but not too hot), dry, and no major wind events. A month like May of 2017 is a great example of what we're hoping for. That month, our average high was 78.4°F (with our hottest day topping out at 94.2°F). Our average low was 45.7°F (with our coldest night bottoming out at 35.8°F). We saw just 0.18" of precipitation for the month, and no major wind events. June warmed up further and stayed dry. Sound like this year? Not exactly. Because of our late budbreak, we didn't see the early stages of flowering until mid-May, and didn't finish until the second half of June. If you look at this year's flowering period (so roughly the last 10 days of May and the first 20 days of June) our average temperature was 74.2°F, more than four degrees colder than last year's flowering period even though it was three weeks later this year. We didn't have any significant rain, and wind was moderate, but eight days topped out at 65°F or below.

When you have cool, windy, or rainy weather during flowering you can get shatter, or the incomplete fertilization of the flowers and a resulting snaggle-toothed look of a cluster with only some of its berries, like this Grenache bunch:

Different grapes have different proclivities toward shatter, with Grenache being amongst the most shatter-prone. Shatter is far from universal around the vineyard this year, but it's also more prevalent than I can remember seeing in recent years. 

Sunburn

Unlike shatter, sunburn is pretty much exactly what you think. If it's really hot for an extended stretch, exposed grape clusters can suffer direct damage as cell membranes break down, compromising a berry's skin and allowing the liquid inside to evaporate away. The result is hard, brown, sour raisins, as in this west-facing Grenache cluster: 

The temperatures required to cause this sort of cellular damage in grapes is typically around 125°F. Even in a climate like Paso Robles, we don't ever see ambient temperatures this hot. But fruit that's exposed to the sun can see temperatures 20°F-25°F higher than the ambient air. So, when the temperatures top 100°F, we start to be at risk.

Why would a cool year like 2023 set us up for sunburn damage? Because opening up the clusters to the sun can accelerate ripening and can also significantly reduce your risk of a mildew outbreak by allowing the easier circulation of light and air. That is one reason why many vineyards tie up their canes in early summer, and some even pull leaves away from the fruit zone to further help along this process. These techniques more often come into play in a chilly year, where mildew risks are elevated and where you have reason to worry that you might not get the fruit in before the winter rains start.

Even in this overall-cool year, we've had 13 days top 100°F, including nine in a two-week stretch in late July. We were fortunate that none of those days were hotter than 104°F. When you start to get up closer to 110°F it becomes more and more of an issue. We do what we can to make sure that the clusters are shaded by the canopy. And there isn't much sunburn out there. But there's some.

Millerandage

While we deal with shatter and sunburn to some degree each year, millerandage (also known as hens and chicks) is something we haven't seen much of. Its causes are similar to those of shatter, basically cool or wet weather during fertilization. The result is a mix of full-sized berries and those that are smaller, and often much smaller, like this Syrah cluster: 

Typically, these tiny berries don't have seeds and therefore don't get the same attention that the larger berries do from the plant in ripening. That can mean that when the larger berries are ready to pick, the small ones can still be green, hard, and sour. That always means reduced yields, but often isn't a big deal in quality as those smaller unripe berries stay connected to the clusters during destemming and never make it into our fermentation tanks.

What Does All This Mean?

There is bad news, good news, and news we don't know yet. The bad news is that all three of these issues reduce the quantity of fruit that is available for us to harvest and ferment. I had been hoping for a plentiful vintage (this would have been our first such vintage since 2017) but instead I'm now hoping for something more like average. A silver lining is that after all our rain this past winter, we could afford to see some reduction in crop. In fact, if we hadn't gotten some shatter, we'd likely have to have thinned the fruit pretty aggressively. And if this chilly spring had happened after a dry winter, the starting cluster sizes would have been smaller and we could be looking at fruit levels more like a frost or severe drought vintage like 2011, 2015, or 2022. I don't think that will be the case.

Other than the "it could have been worse" the best news is that none of these three issues are typically negatives in terms of fruit quality and can even be an asset. Quantity will be negatively affected, sure. But in terms of quality we're looking at a very strong year. Berry sizes are small. Clusters are loose and therefore less prone to mildew and rot. Yields per acre should be right in line with our favorite years. We should see outstanding intensity in what we harvest.

There are two things we don't know yet. The first is just how much these three issues are likely to reduce our yields. Typically, we estimate crop by counting clusters and using average cluster sizes. The wide variability between clusters because of shatter and millerendage make estimating more difficult. Plus, different varieties appear to have been impacted to different degrees. The second thing that contributes to uncertainty is that we're still a long way from harvest. If we don't start until mid-September, as I'm guessing, and don't finish until mid-November, that's at least a month and as much as three months for other unknowns to take place. Last year, we had the worst heat wave in our history in early September. There have been years where we've gotten significant rain in October. There could be fires. Heck, next week it looks like we might see some precipitation from a tropical system that is forecast to wander into southern California.

If 2023 is teaching us anything, it's not to count our chicks (and hens) before they're hatched. Stay tuned.