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Late Ripening – How to Deal

Late Ripening: Recalibration of Fruit Ripeness Numbers

The delayed ripening we see in many Washington state vineyards poses some challenges. With good will from Mother Nature, good work in the vineyard, and some extra efforts in the winery, this season should produce excellent wines. But we want to be prepared–just in case.

The major problem will be logistics. It looks like we might have a very compressed grape harvest period with long working days and tight tank space. Of course, if Mother Nature gives us a beautiful long fall, all our fruit will ripen with intense flavors and good sugar and acid balance–and this letter will not have been necessary at all.

Recalibration of Fruit Ripeness Numbers

Several winemakers and grape grower are seeing attractive fruit flavors in some fruit. With the cool summer we have had, it seems that attractive, ripe flavors are developing at lower sugar content (Brix) and higher acidity than usual. We might see ripe Sauvignon Blanc at 20-22 Brix, ripe Riesling perhaps as low as 19-21 Brix, ripe Merlot and Cabernet near 21-23 Brix. Due to the cool weather the acidity remains higher than in usual, warmer, summers. Titratable acidity (TA) of 9 to 11 g/L and pH of 3.0 to 3.2 in must of white grapes is not at all bad, or unusual for cool climate conditions. In red grape varieties we would expect the range of TA to be 7 to 9 g/L with pH 3.2-3.4. With less fruit sugar we potentially will have less alcoholic wines (10-12.5% in white and 11.5 to 12.5% in reds). It is legal to use additional sugar if your juice is 21 ∞Brix or less to bolster the alcohol content; however, it is only legal to improve the alcohol concentration to a final concentration of 14% (v/v). In our experience, modest increases in alcohol are better and we recommend 1 to 2 ∞Brix additions to increase the final alcohol content of the wine by 0.5 to 1.0% (v/v).

With higher TA in white wines, it would be a good strategy to use malolactic fermentation (MLF) in most of the white wines. Besides lowering the acidity, MLF also helps reduce green, vegetative flavors in the wine. In Chardonnay and Sauvignon Blanc, especially, experience has shown that ripe fruit flavors can be enhanced with MLF. MLF is primarily known to alter wine mouthfeel by making it more viscous (rounder, fuller). MLF is not commonly used with Riesling, though in some areas of Germany it is used. When MLF is used, it is often used on a portion of a wine lot and later blended with the non-MLF wine. Because of the danger of MLF in the bottled wine it is necessary to sterile filter both lots and use sufficient SO2 during storage and at bottling.

The point of this discussion is to alert winemakers to expect ripe fruit flavors at lower sugar content and higher acidity. Since the majority of aroma compounds are found in grape skins it is very important to taste the skins separate from the pulp and seeds. The difficulty is that most of the fruity aroma compounds in the grape are pre-cursors and are undetectable to human senses. However in varieties that are known to make vegetable aromas such as Sauvignon blanc, Cabernet Franc, Cabernet Sauvignon, Merlot, the skin can be used to determine how ripe the fruit is. Since the methoxypyrazines (compounds responsible for veggie aromas) decrease post-veraison this decline will have to be monitored closely if the cool temperatures persist, as it will slow the process. The pulp of the berry where most of the sugar and acid is accumulated will taste less sweet and more acidic. More acidity might give the impression of unripe but look for ripe citrus, tree fruit, berry and spice flavors. It can be expected that flavors will change very quickly as we get more sunny, warm days. Check fruit maturity frequently and be ready to harvest (at lower than usual sugar content)!

Uneven ripeness

Most vineyard managers have already dropped fruit before vÈraison to make sure that the fruit that remains on the vine will ripen evenly in a shorter season. At vÈraison, clusters that were lagging behind in ripening were dropped. These late clusters will not catch up to the maturity of the earlier clusters.

At this time, the most important thing is to taste the fruit in the vineyard to see if there are large variations in ripeness. If possible, harvest and ferment the fruit of different ripeness separately. If this is not possible, hand harvested fruit can be sorted on sorting tables at the winery, remove the firmer berries (taste occasionally), separate the less ripe fruit for a separate fermentation.

Under-ripe fruit should be pressed lightly and the must might have to be de-acidified to achieve a final acid balance without having to make large acid adjustments in the wine (best to avoid making acid adjustments in the wine larger than 1 g/L).

Heat!

Experience from winemakers in Burgundy, Washington, Oregon, Germany, and New York about red wine vinification.

You need heat (68-95∞F) to make great red wine (of course, this is in addition to flavor-ripe grapes and good microbial hygiene).

One critical obstacle in cool climate regions to making great red wines has been that the fruit is cold and it often does not reach sufficiently high temperatures to allow best color and flavor extraction. If you are a practitioner of the ìcold soakî technique (holding juice at 41 to 50∞F for different time periods) this may save you some money but you are eventually going to have to heat up the must for fermentation. When you ferment, it is critical to warm the crushed (red) fruit or the clarified white must to 68∞F as quickly as possible (ideally within a few hours). In these situations it is better to inoculate with an active yeast culture to avoid spoilage problems. Inoculation is done at 68∞F with an active yeast culture that has been rehydrated at the same temperature to avoid temperature shock. Two available options for optimizing your fermentation are available and we outline them below.

  • Option 1: Allow the temperature to rise early (within the first 3 days) to 95∞F (this likely will require some additional heat) and then allow the wine to cool or actively cool to between 77 and 86∞F, then finish the fermentation at 68 to 77∞F.
  • Option 2: Start fermentation at 68∞F and slowly allow the temperature to increase towards the end of fermentation near 86∞F. Then, after completion of alcoholic fermentation, heat the wine to about 104∞F and hold this temperature for 1 to 2 hours (closed tank, blanketed with CO2). If warming the wine to 104∞F you kill the native malolactic bacteria and you will have to inoculate with a ML starter culture when the wine temperature is back to about 70∞F.

Option 1 is a technique used for problematic fruit (moldy or rotting fruit, Botrytis) and will help slow down any unwanted organisms or blow off any off-flavors. Fining agents can also be used to remove some unwanted aromas (see WSU Extension Manual EM016).

Option 2 is used if the fruit condition was good and there appears to be no fermentation problems (odd odors, etc.). The extra heat at the end of alcoholic fermentation helps remove unwanted green, vegetative flavors and increases mouthfeel.

CAUTION

There are some problems with high temperature because high temperatures will kill yeast. This effect is modulated by alcohol concentration though. A temperature of 95∞F and less than 5% (v/v) alcohol does not to kill the Saccharomyces yeast. However temperature of 95∞F and 12% (v/v) alcohol (end of fermentation) will start to kill essentially all yeast and bacteria. Thus, to avoid stuck fermentation keep the fermentation temperature between 68∞F and 95∞F and use heat treatments like those described early in the fermentation or only after completion of alcoholic fermentation.

For under-ripe fruit (green or grassy aromas, green seeds with lots of tannins), one option is to heat the destemmed fruit, press, and ferment the red juice. A second option is to heat the must, ferment on skins and press off before alcoholic fermentation is complete (to avoid extracting to much tannin and green flavors). Alternately you can crush, ferment, press off early and heat young wine (104∞F). Experience has shown that heating of must to either 140∞F for about 20 minutes (with slow cooling) or to 190-195∞F in a closed system (tube in tube heat exchanges) for 2 minutes does reduce unripe flavors. To start the fermentation the must temperature must be back down to about 70∞F.

Botrytis and powdery mildew infected fruit should be heated in the same way, either to 140∞F for 20 minutes or 190∞F for 2 minutes. A couple of different options for doing this are available with portable heat exchange units. Alternatively as discussed earlier the wine can be treated right after alcoholic fermentation by heating to 104∞F for 2 days or 140∞F for 2 minutes. Wine can be heated in a tank (blanketed with CO2) to 104∞F, to heat wine to higher temperature, a tube in tube heater that excludes oxygen should be used. The heat treatments will kill the mold and more importantly inactivate a very potent oxidizing enzyme (laccase) formed by Botrytis cinerea.

Yeast nutrients

Cool growing years and low maturity grapes tend to have low amounts of yeast available nitrogen (YAN). You should check the YAN in the grape must and make additions of diammonium phosphate and complex yeast nutrient blends in the first third of the alcoholic fermentation. It is best to add the yeast nutrients in two separate additions. Remember, yeast cannot take up ammonia and amino acids towards the end of fermentation. The goal is to have a minimum YAN of 240 mg/L.

Yeast strains

Different yeast strains have a strong influence on the final wine flavor profile. Experience has shown that some yeast strains are better in enhancing ripe, berry and plum flavors than others. It is worth experimenting with different strains! Also, leaving wine on yeast lees does enhance ripe fruit flavors ñ especially in white wines (including Riesling). Fresh yeast (carefully rehydrated to manufacturerís instructions) can be added to the wine for extended lees aging. Lees that contain a higher amount of grape pulp (cloudy must) should not be used for extended lees aging as such lees have a tendency to produce reduced sulfur off-odors. Smell the wines when stirring the yeast! Yeast lees stirring is only necessary about every other week. It is best to do extended lees contact in barrels or in tanks with low height and wide diameter. This allows more contact of the wine with the yeast lees.

ATA in the second year after drought stress

Research in New York state on atypical flavor (ATA) defect in white grapes has shown that ATA can also occur in the fruit of vines that had been water and heat stressed the previous year. Thus, if you are using white fruit from a vineyard that did suffer heat stress last year, be prepared to use ascorbic acid to protect the wine from ATA. Ascorbic acid (150 to 200 mg/L) should be added after completion of alcoholic fermentation and as soon as the wine has stable free SO2.

We are looking forward to a cool ripening period for our grapes. Flavor ripening might be proceeding rapidly now!

Thomas Henick-Kling and Jim Harbertson