Sour Grapes, Sweet Solutions: How Verjus Could Help Winemakers Beat the Heat

Welcome back to The Wine Lab, the podcast where we dive into the fascinating world of wine, through the lens of science, sustainability, and sensory exploration. I'm your host, Andréa Bottasato, and in today's episode, we explore an age-old ingredient with a bold new mission - verju. That's right, tart, unripe grape juice, once a staple in medieval kitchens, may now hold the key to solving a very modern winemaking challenge. Rising pH and falling acidity in wines due to climate change. We'll be sharing insights from a recent study conducted at Texas A&M University by Andréa Lynn and myself. Grab a glass, and maybe a notebook, because this is winemaking innovation at its greenest. Let's start with a problem. In hot climate regions like Texas, grapes ripen quickly. That means higher sugar levels, high pH, and low acidity. And those three things together? Not great for wine quality. We're talking about flabby, microbiologically unstable wines that oxidize too quickly and don't age well. Traditional fixes like adding tartaric acid work, but they come with limitations, cost, potential instability, and sometimes a sensory imbalance. But what if we could fix the problem naturally using something already growing in the vineyard? Enter verju. Verju is juice made from unripe grapes, usually discarded during cluster thinning, a vineyard practice used to balance yields and ripening. Instead of wasting this green gold, the researchers turned it into a sustainable acidifier. The big idea? To use verju to lower pH, raise acidity, reduce alcohol, and make wines more balanced, all while repurposing vineyard waste. In the study, we'd made muscat canneli wines from ripe grapes and acidified them using two treatments, one with 2% verju addition and one with 11%, alongside a control with no verju. Yes, verju worked and impressively so. The 11% addition dropped pH from 3.6 to 3.3 and boosted titratable acidity from 4.1 to 7.1 grams per liter. That's a major improvement in wine stability and freshness. Malic and tartaric acids also increased thanks to their high levels in the verju itself. And as a cool bonus, the alcohol content dropped by over a full percentage point from 14.3 in the control to 13.2 in the most acidified wine. That's because verju dilutes sugar concentration in the must. It's like getting a wine with better balance and lower alcohol without fancy equipment or added chemicals. Now let's talk taste. Our team ran a consumer preference test at four Texas wine industry events with 218 tasters. What did we find? When asked to rank the wines based on preference, participants couldn't tell them apart statistically. No treatment stood out as better or worse. That means verju additions didn't negatively impact sensory quality. But when it came to perceived acidity, tasters got it right. The most acidified wine tasted the most acidic, the control the least. So verju changed acidity perception without hurting drinkability. Why does that matter? This isn't just academic. This approach could be a game changer for hot climate viticulture. It is sustainable, repurposing grapes that would otherwise go to waste, practical, there's no new equipment needed, and profitable. The same study showed that making and selling verju could offer wineries a new revenue stream. Verju acidification isn't just a technique. It's a climate smart strategy and it might just be the taste of the future. That's it for today's episode of the Wine Lab. If you'd like to dig deeper into the research, check out the full paper in Eno1 and the link posted in the description. Thanks for listening. Until next time, stay curious and stay fermenting. Cheers!