(CN) --- As temperatures continue to soar and more crop types are affected by climate change, winemakers in California’s San Joaquin Valley are looking for inventive solutions to keep the sauce flowing. The sauce must flow, after all.
Grapes can be a particularly finicky fruit. If temperatures get too high --- or merely too high at a crucial stage --- if the vines get too little water, or too much, or any other myriad factors, that rich fruity cab with those delectable fruity notes can quickly devolve into swill. As climate change continues to push temperatures upward and droughts have become a fact of life in California, many of the state’s vintners worry about what’s to come.
Researchers from The University of Adelaide in Australia and the E. & J. Gallo Winery in Modesto, California, teamed up to tackle the problem in a study published Wednesday in the ACS Journal of Agricultural and Food Chemistry. They studied cabernet sauvignon grapes at a commercial vineyard near Lodi where the vines were planted in 2010.
“Grapevine physiology has been affected by changing climate conditions and higher frequencies of heat and/or water stress events have had remarkable repercussions for grape and wine quality traits,” the study authors wrote. “Accelerated sugar accumulation, and hence changes in the synchrony of primary and secondary compounds at harvest, remains one of the most challenging consequences of climatic conditions exceeding the optimal range for grapevines.”
Grapes mature through a delicate process on the vine, changing colors while accumulating just the right balance of flavor and aroma compounds depending on the variety and growing conditions. If stress from heat or lack of water causes the grapes to ripen too quickly, they can turn out with the less-than-desirable taste of overcooked fruit. Winemakers want enough sugar in their grapes to achieve the flavor they’re after --- but not too much --- and it’s always a balancing act.
“We employed different techniques to explore the nexus between ripening rates and grape chemistry, with a focus on grape aroma compounds,” said the authors in their study. “PCA [principal component analysis] highlighted that grapes followed a tightly regulated ripening program and that maturity levels explain the largest variation in grape chemistry, in agreement with other studies.”
The researchers found that by delaying the ripening process, winemakers could ensure their grapes don’t take on any undesirable traits due to stress, even under increasingly suboptimal conditions. They found two techniques that together do the trick of slowing down the ripening process: increased pruning and late-stage watering.
By culling around 35% of the grapes shortly before they begin to ripen, the remaining fruit has better access to critical nutrients that would otherwise be divvied up among their peers, but on its own that causes grapes to ripen faster. On the other hand, watering the vines by 50% more than usual late in the season reduces berry dehydration, increases sugar concentration and ultimately slows the ripening process. Researchers found that grapes displayed the slowest rate of sugar accumulation when these two practices were combined, resulting in a tastier product, albeit less of it.
Delaying the ripening process results in lower levels of certain compounds that can lend wine a distinctly vegetable flavor, while at the same time increasing norisoprenoids and terpenes associated with infinitely more desirable fruity and floral notes, according to the authors. They said the new strategies outlined in the study will need to be studied further over the next few years before commercial winemakers begin to incorporate the practices described.
“Our study provides an important confirmation that delayed ripening is beneficial to improve the quality of grapes for winemaking,” the scientists wrote. “Several authors have tackled this topic from the perspective of wine composition, whereas here we reported changes in grape chemistry under three regimes of sugar accumulation within the same commercial vineyard block.”
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