The appassimento method, which uses partially dried grapes to create deep, intense, and often long-aging wines, is responsible for one of Italy’s most remarkable and famous wines: Amarone. Amarone is made near Verona in Northern Italy. It can be sold at very high prices and often sits in collectors’ cellars for decades. In recent years, the method has also found a new home in Canada’s winemaking region of Niagara in Ontario, where it has gained popularity as a way to produce more powerful wines despite the relatively cool climate.
This growing interest in creating a distinctive regional style has also led local researchers from the Cool Climate Oenology and Viticulture Institute (CCOVI) at Brock University to take stock of the special challenges that come with the appassimento technique and to find ways to address specific issues. Over the last five years, Dr. Debbie Inglis, the director of CCOVI, along with her colleagues and students at the Institute, as well as industry and other research partners, looked at issues concerning the drying process, the effects of botrytis and, in particular, a new avenue for avoiding acetic and oxidative issues during fermentations.
Cool and steady
One of the main challenges facing appassimento winemaking, whether in Canada, Italy, or anywhere else, is to ensure the drying concentrates the juices and flavors of the grapes without creating other issues. Leaving the grapes in open air makes them particularly susceptible to developing oxygen-related issues like higher levels of acetaldehyde, ethyl acetate, and volatile acidity (acetic bacteria responsible for volatility thrive in aerobic conditions). The quality and sanitary condition of the grapes when they are set up for drying, as well as the drying conditions themselves, can have a significant impact on the production of these oxidative compounds in the grapes, which will then inevitably have repercussions on the wine.
Inglis and her team looked at grape drying under five different conditions: on the vine, in a barn, in a greenhouse, in a drying chamber, and in a kiln. Kilns had been put to use by some of the Niagara wineries using the appassimento method, before the study started, with the idea that drying the grapes quickly in a hot and dry environment would be more effective and less susceptible to the issues that could arise during longer drying.
It turns out that it’s a bit the opposite: In kiln-dried grapes, acetic acid levels rose significantly more than in any of the other methods. It seems like higher temperatures had more influence on acetic acid levels than long exposures to air. The rise wasn’t catastrophic, though, as concentrations in the grapes remained around 0.13 g/liter, when they came out of the kiln—well below levels that could be seen as deeply problematic, at that point.
All drying methods caused a certain rise in acetaldehyde, with no notable difference between them. They also caused a rise (between 10 and 30 percent) of the amount of polyphenols present in the grapes, something that aligns with creating a wine that has a bigger mouthfeel and more structure.
As far as botrytis goes, the team didn’t find any significant problems with its presence in up to 10 percent of dried grapes, with flavor profiles and fermentation dynamics remaining largely the same, the biggest differences being the rise in glycerol levels, which were multiplied by four, something which would likely affect texture by making it a bit rounder.
A special yeast
Even though the rise in oxidative compounds wasn’t catastrophic at the drying stage, the concentrations are still higher than normal at the time fermentation starts, and things like acetic acid can rise significantly during vinification, if the right conditions are present.
Enter a newly isolated yeast strain found by the CCOVI team: Saccharomyces bayanus, which was first identified as a naturally present, indigenous yeast in Riesling ice wine grapes.
That isolate was originally considered as an interesting strain for ice wine production, but didn’t do well on its own in the high-sugar environment of that slow-fermenting sweet wine. Its characteristic is that it considerably limits the growth of oxidative compounds in the fermenting wine, thereby providing a preventive effect.
In the trials performed by one of Dr. Inglis’ PhD students, Jennifer Kelly, the levels of acetic acid and ethyl acetate rose half as much in ferments using Saccharomyces bayanus, compared to ferments using a commercially-accepted strain, EC1118. Alcohol levels were essentially the same, and the general flavor profile was at least as favorable, in consumer tastings, as with more traditional fermentations.
In searching for specific solutions for the dried grapes, the researchers seem to have found a solution that could be interesting for winemakers in any style, beyond appassimento, to respond to potential oxidative issues. For grape varieties that can be susceptible to volatile acidity, or in cases where the sanitary condition of the grapes is problematic (say, when there is lots of rain and disease pressure, just before harvest), it could be beneficial to be able to include in their toolbox a yeast strain that could prevent oxidative problems without affecting the flavor profiles—and allowing the winemakers to avoid other interventions like higher sulfur additions.
A video presentation by Dr. Inglis from March 16, 2016 is now available for viewing on the CCOVI lecture series web page.