Selecting the Right Clusters for Your Wine

This article will appear in the Wines of Canterbury Newsletter

"Quality is never an accident" - usually attributed to William Foster or John Ruskin

Colour change and ripening has begun in our grapes, and a lot of people start thinking about cluster thinning at this time. But have you stopped to think about why you're doing this? Here are some possible answers and few thoughts on each:

• To reduce the crop load

Yes, true. But it takes time and money to do this, and at the same time, you're reducing the amount of fruit harvested and paid for. There has to be more to it than this!

• To make the winemaker happy

At the recent International Cool Climate Symposium for Viticulture and Oenology in Tasmania, Richard Smart said the best time to start thinning your crop was just before the winemaker visited the vineyard, and the best time to stop was as soon as he left!

The best way to make the winemaker happy is to deliver high quality fruit in relation to what they are paying. Do all winemakers know enough about viticulture and the production of high quality grapes to be able to tell you what is and isn't right for the vines? Some do, but many don't. Their heads should be filled with all things winemaking, and viticulturists' should be filled with all things viticultural.

The best thing to do is get the winemaker to tell you what s/he wants from the vineyard's fruit, and for you to do what's necessary to have fruit that most closely meets those needs. Sometimes, removing lots of fruit is not the answer!

• To increase sugar accumulation in the fruit

If you go through a vineyard at veraison and remove fruit randomly, I doubt there would be much, if any difference in the harvested fruit composition - that is, the rate of sugar accumulation in the remaining fruit is no faster because you've removed some crop. I haven't seen any consistent and convincing evidence to suggest that removing crop randomly this late in the season brings harvest forward.

However, if we do commercial practice and remove that fruit which is not as ripe as the rest (in the left side of the figure below), then we're decreasing the variability of that fruit by removing the less ripe stuff, and thereby increasing the average ripeness of what remains. So what's happening there is removal the tail end of ripening fruit.

By doing this, you can increase the quality of the resulting wine, which is the overall goal of the viticulture-wine making pathway that we all travel along, and therefore the goal of crop thinning.

Because fruit are being removed selectively, and there will always be some fruit that lags behind in development, this form of thinning can be effective in improving wine quality in any season - particularly in cooler climates, where getting fruit to its optimum ripeness is a challenge.

But it doesn't stop there. If we want to maximise the quality of the wine made from the grapes, we need to ensure that only the best quality fruit ends up in the receival bin at the winery. This process continues on from crop thinning to monitoring the fruit and fixing problems before they arrive, so you have the greatest amount of harvestable crop possible. Things to think about here are:

• Removing leaves resting directly on clusters. Airflow around and if possible, through, clusters is a very important part of keeping Botrytis at bay! Leaves on top of, or resting next to, clusters keeps the environment more humid and for longer, which is what Botrytis needs to germinate and infect.
• Similarly, arranging clusters so they are not draped on top of one another. Multiple clusters trying to occupy the same space mean restricted airflow and poor exposure to the sun, leading to greater disease risk and less ripe flavours. The best time to combat this is even a few weeks after fruit set, when it's easier to separate clusters and try to arrange them so they don't touch. If you can't keep them from sitting on top of one another, take the short term loss by clipping off of one of the clusters rather than doing nothing and having the real risk of losing all the fruit to rot.
• Cutting out clusters or parts of clusters damaged or diseased. Physically damaged fruit can, and usually does, harbour Botrytis - something most evident when a couple of weeks ago I took a few split berries i found in the vineyard (like those pictured below)  and incubated them in high humidity conditions for a day or two. Lots of fungal growth appeared from the damaged areas, but none from the intact parts of the berry. As well, fruit that has a bit of Powdery Mildew on it can split when the berry starts to ripen, inviting Botrytis and other rot organisms. Once it's in and established, it's much more likely to spread around.
  
  
  
  
  
• If you're machine harvesting, have a crew go through beforehand to remove any second set crop that might also be harvested, because even a small amount in a load can have a significant effect on wine flavour. As well, have them take out any diseased or sunburnt fruit, as these can lower the quality of the wine. Monitor their work for slips and keep them on the right track.
• If you're hand harvesting, the best time to sort grapes is in the vineyard, not on a winery sorting table. Why pick and transport poor quality and diseased fruit, only to discard it at the winery? You make more work for yourself, and increase the risk of spreading the disease around. Make sure your picking crew is well trained to leave the undesirable fruit, and check on them periodically to make sure they continue to do it right.

While this is all sound advice, I'm not trying to say that it's right for everyone. For some wine products, this level of attention to detail is not warranted - there just isn't the payback to justify it. However, if you're thinking about quality first, then every little bit counts. There isn't one, single, management decision that will deliver quality to the winery - it's a series of actions that contribute to the health and suitability of the harvested crop that makes the difference...