Brix, Not Maturity Pressuring Winemakers into Hasty Harvest

Growing Bulletin - September 2017

Last week we emerged from two long and searing heat waves that abruptly ended what had been a rather mild August in the North Coast. Due to the resulting spike in sugar levels, some winegrowers are be feeling pressure to harvest stressed and underripe fruit well before they reach the phenological and physiological maturity milestones that are linked to high quality luxury wine. When the first heat spell arrived last weekend, we had just passed 104 days since bloom and not even 30 days past veraison for many varieties on the North Coast.

Today marks 120 days since bloom and only 38 days since veraison*
And what is trailing average Days Bloom to Harvest (DBH) and Days Veraison to Harvest (DVH) for Cabernet Sauvignon over the past 15 years? 133 days and 68 days respectively. We have a little ways to go.

While the recent weather has pushed Pinot Noir from "not quite ready" to "high gear", the varieties most at risk are the earlier ripening Bordeaux varieties (Merlot, Cabernet Franc, Malbec). These early varieties saw sugar levels spike due to heat and dehydration but need a bit more hang time. We have seen just a few of these fermentation samples of high brix Merlot and Cabernet Franc—and they are not very good. Expect to see low color and high tannin in any high brix, but physiologically underripe grapes from that were hammered by the heat and/or are harvested before our models predict maturity. The late ripening varieties such as Cabernet Sauvignon and Petit Verdot will hopefully have some time to recover with cooler weather and abundant irrigation.

How to help vines recover?
Irrigate, Drop damaged fruit, Measure grape quality, Plan fermentation strategy based on chemistry for each pick.

Figure 1. Current weather conditions and 7-day forecast for St. Helena, CA as of 12:00 PM Monday, September 11, 2017. Click the image for the live version on our website.

Weather Outlook and Maturity Models

Showers and thunderstorms will move south-to-north across the region through tonight. Showers will also continue through Tuesday and into Tuesday night. Slightly cooler temperatures are forecast Tuesday, with much cooler weather expected by midweek and beyond.

An upper low southwest of San Luis Obispo County continues to slowly progress to the north while pulling in moisture from the southeast. Models have been struggling with the convection, but general thinking is that showers and possible thunderstorms will head into the Bay Area and North Bay this evening. Rainfall amounts should mostly be under 1/10".

Temperatures will be cooler tomorrow with deepening marine layer. Rainfall amounts will again be mostly light although any strong cells could have heavy rain or even small hail with them.

Showers and thunderstorms will continue to shift to the east on Wednesday ending the convection. The marine layer is forecast to deepen and onshore flow will be more pronounced. Highs will be back in the 60s and 70s for most spots.

Longer range guidance indicates a gradual warming trend through the weekend. No rainfall is forecast for Wednesday through the end of the week.

Our model has been pointing to October 5th as the grape harvest date (GHD) using both days bloom to harvest (DBH) and days veraison to harvest (DVH). These models were developed over the past 13 seasons, and corroborated by heat summations using Huglin Heliothermal Index*. Our model predicts 135 DBH and 70 DVH.

Figure 2. (Top) 2017 Daily temperatures vs historical averages record temperatures in St. Helena (Bottom)) Huglin Heat Summations for 2017 compared to past years for St. Helena weather station.

What to do Now

What is a winemaker to do? With cooler temperatures offering a reprieve, water is your only tool to ensure that brix levels revert now that more seasonal temperatures will set in for a while. Irrigate aggressively! Our typical recommendation during the final few weeks before harvest is to water at a minimum rate of 8-10 gallons/vine/week. The best performing vineyards we have seen so far in our client base were protected with misters in the canopy and were irrigated at a rate of 12 gallons/week in the days leading up to the heat spells. The water requirements will be greater due to the elevated temperatures. Now is also the time to send your cluster samples in to get a sense of your vineyard block quality.

Drop damaged fruit
Work closely with your vineyard manager to drop burned or heat damaged fruit if you have not already. We suggest making one pass now and following up with another in a week to ten days.

Measure grape Quality now.
Get quality measurements now, and again in 7-10 days. Tracking color development regularly in the vineyard is imperative from this point forward, especially for problem blocks to create a customized fermentation plan.
Grapes harvested before reaching full maturity will contain low color and high tannin due to immature seeds, in addition to underripe flavors. We recommend submitting cluster samples from the crush pad in all of these cases, knowing that we can expect to extract 100% of the tannin, but less than 70% of the anthocyanin chemistries critical for high quality wine.

Fermentation strategy
Once we know the potential within the grapes, we can predict the outcome and make an appropriate modification to their standard fermentation plan (SFP).

With the color and quality variability this year, your Standard Fermentation Plan (SFP) should therefore minimize tannin extraction. It is always a good strategy to make a light wine from first few tanks than over-extract. Sample first fermenters at 18, 12, 6 and 0 °Brix to confirm extraction and fine-tune your SFP.

Grape Quality So far in 2017

It is no surprise to us that grape tannin levels are absolutely excessive, and the Aging Index is the lowest we have seen so far in this young harvest season.

We are seeing that geography, exposure and solid type explains color and quality variation in the vineyard, not Brix. Analysis from roughly 40 Merlot grape samples show tannin ranges from 800 to over 1500 ppm with Complex Anthocyanins from 135 to over 270 ppm. While this wide range can be considered normal for this early in the season, we normally see stronger correlation between grape chemistry and sugar levels. This is yet another data point that tells us the brix are not aligned with maturity.

So far Pinot Noir extraction appears to be on the low end of the spectrum, but that is typical for the first week of harvest as winemakers are dialing in the fermentation protocols. Some fermentations are extracting higher levels of tannin than we have seen in the past. We now have enough samples to start assembling some trends in grape development and extraction. Look for more data in the next bulletin early next week.

Summing Up

Below are ere the main recommendations you should be doing:
1 Irrigate aggressively. 10-12 gallons/vine over the next week isn’t too much.
2 Work with your vineyard manager to drop any damaged fruit. Make multiple passes over the next 7 days
3 Send Cluster samples to track color and quality accumulation and make your SFP.
4 Don’t Panic! The maturity models are not close to being aligned with primary chemistry, Enologix quality measurements and calendar date.

Look for a harvest bulletin in the next few days, where we will report the latest trends in the vineyard and the first extractions for the year.

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