Today’s guest post comes to you from the Southern Hemisphere! Luckily, through a LinkedIn connection (yes, sometimes LinkedIn IS useful), this PD was able to farm out an enology post to a knowledgeable and enthusiastic Ohioan, who happens to be on the other side of the planet. Andy Kirk is a MSc (Horticulture) candidate at Lincoln University in New Zealand, and an alumnus of The Ohio State University. Having grown up in Akron and Canton, he worked under the employ of Arnie Esterer at Markko Vineyard in Conneaut for much of 2011 and 2012. He enjoys New Zealand, but often finds himself relating his viticulture and enology learnings back to the shores of Lake Erie. Many thanks to Andy, and for you, dear readers, enjoy!
Flavonoids: The Name of the Red Wine Game
All scientific content here, unless otherwise noted, is drawn from Cultural Practice and Environmental Impacts on the Flavonoid Composition of Grapes and Wine: A Review of Recent Research by Downey, M. O., Dokoozlian, N. K., & Krstic, M. P. (2006)
We’ve all been there once. You eagerly arrive at an Ohio tasting room and are busy being thoroughly impressed by the wine production happening right under the nose of the average Buckeye State resident. The Rieslings are crisp; the Chardonnays are robust; and the Sparkling Pink Catawbas are fun and important to our history. Then you move on to the Pinot Noir and maybe the Chambourcin, and they are just that little bit unusual. What’s going on there? The explanation may lie in the way grapes develop the flavonoid class of phenolic compounds, which includes tannins and anthocyanins. This group of compounds plays a critical role in all the key elements of red wine, such as color, astringency, and mouthfeel. In “big-time” red wine regions, contract growers are now often paid by the phenolic compound, so to speak. With that in mind, let’s look at the synthesis of these compounds in Vitis vinifera and French hybrid grape varieties, and see what we can do to influence flavonoid production in the Great Lakes’ climate.
First of all, what are these flavonoid compounds, and what is their purpose? They are secondary metabolites, which means they don’t have a direct role in the normal, every-day activities of the plant, such as growth, development, and reproduction. That, of course, leaves a wide variety of shoes to fill. One interesting example of these functions can be found in anthocyanins, which are responsible for the pigment in red wine. It is thought that the pigment in grapes makes them more visible and, hence, attractive to birds, which, in turn, improves seed dispersal. Some flavonoids provide defense against the potentially damaging UV-type rays of the sun. Many of the other flavonoids have importance internally as antioxidants and are a critical part of the plant’s response to environmental stress.
This brings us to our next question: What factors influence the formation of flavonoids? Well, we all know Ohio isn’t the sunshine state, and that appears to be one of the primary factors impacting flavonoid accumulation. The narrative for the flavonol sub-group, a big contributor to mouthfeel, is relatively clear. Less sunlight equals lower flavonol content, at least for Pinot Noir, Shiraz, and Merlot. In other words, pluck those leaves if you want to be sipping on full bodied red wines at the end of the year. Furthermore, research from OSU in 2007 has confirmed that cluster thinning can increase the concentration of flavonoids in Chambourcin. The rate of tannin accumulation hits its peak early in the season, which means you’ll have to be proactive if you want to have the most impact. Strictly speaking, the link is a bit more muddled between anthocyanins and sun exposure. For decades, it was accepted that sun exposure encouraged anthocyanin accumulation. This may be true for some varieties, but there is evidence to suggest that anthocyanins and sunlight may not be as closely linked as was once thought. However, the benefits of incorporating some sun exposure into your vineyard management practices are many, regardless of how much it affects the color of your wine.
Temperature actually appears to have a stronger role in regulating anthocyanin production in grapes. Interestingly, much of the work here has focused on the negative impact of having temperatures that are too hot. Take that, California! On the other hand, research has shown that a greater diurnal temperature range (day to night difference) results in higher anthocyanin levels. That advantage appears to head back out west. The diurnal range in Northeast Ohio ranges from 15 to 20 degrees during the growing season, whereas it is close to 30 degrees in Napa. We pay a price for those warm summer nights! This mechanism leaves us chasing an anthocyanin sweet spot, where we might find temperatures in the low 80s (<30° C) during the day with cool nights to follow. In terms of management, this might mean that we hold off on leaf plucking on the west side of the row, sparing it direct exposure to the intensely hot afternoon sun. The research has shown that berry temperatures can be around 10 degrees Celsius warmer than ambient temperatures when exposed to the afternoon sun. Interestingly, there is not enough evidence to support a strong link between temperature (within a normal range) and tannin development. In fact, tannin levels peak around 2 weeks after veraison, and undergo dramatic shifts in their composition as ripening progresses. These shifts tend to coincide with changes in tannin structure, resulting in a reduction in bitterness. However, since we can’t control that process very well, we’ll have to look elsewhere for now!
The above factors of sunlight and temperature would not appear to be holding Ohio’s red grapes back too much, in the scheme of things. However, our plentiful summer rainfall may be a pretty big thorn in the side of red wine production. In fact, there are a few different issues that revolve around the vigor of our vines. Most commercial vineyards in Northeast Ohio are on a fairly fertile variety of silt loam, known as Platea. These soils are somewhat poorly drained and are rich in nutrients. This is significant for several reasons. First, the concentration of flavonoids tends to increase under mild dehydrative stress because of the lack of dilution. Conversely, the excess water typical to many Ohio vineyards likely dilutes the concentration of flavonoid compounds. Secondly, there appears to be some net increase on the amount of flavonoids produced by the vine, regardless of dilution effects. Whatever the mechanism, Ohio vineyards are typically not going to see the benefits of this action. Thirdly, a vigorous vine changes the architecture of the canopy and tends to create shading, which again inhibits flavonol production and changes the temperature of the berries. Whether it be through excess water or fertile soil, managing this vigor problem is one of the most important things a red winegrower can do.
Luckily, there are some tools at hand to aid the Ohio grower in the quest to manage excess vigor, such as rootstock selection. Vitis riparia rootstocks have evolved over the millennia to thrive in wet and fertile conditions of the Great Lakes, and are a good option for managing vigor in the vineyard. Has anyone dabbled in root pruning? Some recent research pursued this intriguing, albeit costly and invasive, strategy to limit shoot growth by forcing the vine to redirect growth toward root repair and production. Many of you will know that many vineyards in Ohio, Ontario, and New York have installed drain tiling to improve water drainage in the soil.
We’ve already discussed how the canopy management basics, such as cluster and shoot thinning, can go a long way in creating an environment favorable to the production of flavonoids. Remember, though, that direct exposure to the afternoon sun can be a very dangerous proposition. Not only do you risk sunburn, but you also may inhibit the production of the anthocyanins that you want to encourage. Cluster thinning would seem to be essential for quality red wine production in Ohio. Where vine balance might call for more fruit in white wine production, the benefits of concentrating phenolics by dropping fruit in red varieties cannot be ignored.
All in all, there is plenty of reason for optimism with regards to Ohio red wine. Always keep in mind that Ohio ruled the American wine world once upon a time, and for good reason. Areas around the Lake Erie region have longer growing seasons than anywhere in the Midwest. Two or three weeks can make a huge difference in terms of allowing red grapes a bit more time to synthesize compounds and lose that pesky malic acid. Yes, water dilution will probably always be an obstacle, but maybe we need to think outside the box of wine styles! The lovely folks of Beaujolais have made a living for millennia on their light red wines from Gamay Noir. Hmm, perhaps we should save that one for another entry!