Green Pruning to Improve Grape Ripening

So one if the things that can be done to improve ripening of grapes is cluster pruning. Sometimes this is done pre-bloom to improve the flowering of flower clusters left behind and adjust potential crop load to trellising and vine ripening capacity. This is often referred go as green pruning.

Sometimes this crop adjstment is done later in the year if there is the thought that the gapes on the vine are not going to ripen adequately before the end of season. The second cluster may not ripen to the same level as the first cluster and if harvested together, the higher quality first cluster is averaged lower with the lower quality second cluster, potentially lowering the quality of the wine.

When cluster pruning, the second or third cluster is usually removed which concentrates ripening into the remaining cluster.

We have tested about 30 varieties of grapes at our vineyard and it seems as though some varieties ripen the first and second clusters similarly while other varieties show significant differences in ripening between clusters.

See St. Croix below, with visually obvious differences in ripeness between first and second cluster.

Usually we dont cluster prune later in the season but in cooler years when the vine struggles to bring the grapes to adequate ripeness we may employ this technique.

We can usually tell the years that inadequate ripening may be an issue by the timing of veraison. Late veraison means that we may not have enough time and heat left in the season to ripen the grapes to our liking.  So thats when we would consider cluster pruning of the second cluster.

In the past ten years this has happened only once..but this is also because after 10 years we know what the crop load should be for the various varieties we have as it relates to our vineyard climate and conditions. And we also know when the usual timing of veraison is for the various varities.

Refractometer to Test Brix / Sugars

There are lots of ways to get an idea of the ripeness level of your grapes leading into harvest.

The easiest is to taste the grapes to see how sweet they are and what the acid is like. Problem is if your new at this then you dont really have a baseline of previous years experience to assess it against.

Another way is to check the colour and hardness of the seeds in the grape. If the seeds are brown and crack hard when you bite on them then you know the grapes are getting ripe but experience is key here again and the brown of the seeds is not universal for all grapes relative to how ripe they are. Similarly the bunch stem usually turns brown and hardebs off.

One of the most accurate ways is to test the sugar ot brix level of the grapes with a refractometer. These instruments cost about $100 and provide a fairly accurate reading of the sugars in a few drops of grape juice. I taje a sample of about 3 grapes from different parts of the cluster and average the numbers out.

Brix is a measure of sugar content in the grape juice and ripe grapes will usually have between 18 and 24 brix depending in the variety. So in converting brix to alcohol content, 1 brix gives you roughly 0.55-0.6 % alcohol, so 20 brix gives you wine with roughly 11-12% alcohol when fermentation is complete.

I put a small video here to show how the refractometer works. Not the best video but you'll get the idea when you see this.

Grapes Look Good Heading Into Harvest

So checking on the grapes with about 4 weeks before harvest they are looking good. The bird netting is working ok so far but the wasps still get through and the this Robin found a gap and got under the netting. They love the Foch and Millot.

Most of the vines are hardening off the canes well and the grapes are ripening very well. Here is brix readings as of September 8, 2018 and about 900 degree days growing to date.

WHITES
Ravat 34....15 brix
Evangeline....18.5 brix
Seyval....20 brix
L'Acadie.....20 brix
Vandal Cliche....17.5 brix
Petite Milo......17.5 brix
Seigerrebe.....19 brix

Here is Ravat looking very good

REDS
Leon Millot.....16 brix
Marechal Foch.....15 brix
Castel.....16 brix
St. Croix......15.5 brix
Marquette......18 brix
Colmar Precoce Noir ....19 brix
Triompe D'Alsase.....15 brix
Pinot Noir.....17 brix
Lucy Kuhlman....18
Marechal Joffre....18

Here is Leon Millot with canes hardening off well.