Reduction in Mencía, Explained

“Why are mencía wines so reductive?”

I was recently asked this by a very smart wine professional, and I didn’t have a great answer other than “winemaking, I guess.” But that answer felt a bit reductive—see what I did there?— so I decided to dive into a bit of the science behind reduction and why it can sometimes manifest in Galician wines, specifically mencía. I haven’t always found it to be the case that all mencías are reductive. In fact, I love mencía for its capacity to make some of the most transparent, fruit-forward reds I’ve tasted. But there are moments just after opening a bottle when you can tell that something is lurking in the glass. It’s not always strong, but it can be enough to raise questions.

So what is reduction? Strictly speaking, reduction is a chemical process characterized by the absence of oxygen, leading to the formation of volatile sulfur compounds like hydrogen sulfide, mercaptans, and dimethyl disulfide. These can produce aromas that range from unpleasant off-smells to desirable complexity. Common aromas associated with reduction are flint or gunsmoke, cooked or rotten eggs, onions or garlic, sweet corn, and rubber. Although reduction has traditionally been seen as a fault, some wine pros appreciate reductive aromas for their complexity and their potential to enhance a wine’s longevity—since reduction is essentially the opposite of oxidation.

And what about mencía? How does reduction show up in wines made from this grape? I went to my go-to Galician wine chemistry source, Dominique Roujou de Boubée, PhD. He’s worked extensively with mencía at Ribeira Sacra winery Ponte da Boga, and I asked him what the deal is with reductive aromas in Galicia’s most famous red grape.

“We can generally put varieties in a box of oxidative or reductive,” explains Dominique. “For reds, syrah, tempranillo, and mencía are varieties that have reductive tendencies. But while mencía has an inherent tendency toward reduction, it's not a universal trait, he says. “Mencía can have reductive tendencies, but always and not in every soil,” he says. “At Ponte da Boga, we’ve not often had issues with reduction. We also have to factor in terroir, viticulture, and nutrients in the vineyard.”

While there’s clearly a varietal component, he says that reduction is often a reflection of soil health and viticultural decisions. “The fewer nutrients there are in the soil, the more the wine may tend toward reduction. Reduction can appear when the vine lacks nitrogen,” he says. “In poor soils, unfertilized soils, or soils that haven’t been worked a lot, if the grape comes into the winery lacking nitrogen, the yeast, which feeds on nitrogen during fermentation, will end up forming volatile sulfur compounds.”

For Dominique, the reductive expression of mencía has a specific sensory profile. “I always associate reduction in red wines with these aromas of blood and hunting. In Burgundy, there’s a traditional aromatic descriptor, ventre de lièvre, or ‘rabbit’s belly,’ which refers to the scent when hunters would skin a rabbit. Reduction can be a bloody, ferrous smell, like if you put a copper penny in your mouth. You have that metallic touch. So for me, reduction in red wines translates to blood, smoked meat, and metal.”

Winemaking decisions also matter. “From my experience, there’s a facet of vine nutrition, but also an aspect of winemaking. If you raise mencía only in stainless steel and don’t rack the wine, it can develop reductive notes.” Alternative élevage can mitigate this. “Raising mencía in foudre is very appropriate because you avoid that anaerobic environment that can lead to reduction,” he says. “In terms of new oak and used oak, every winemaker has to use the wood that works for them, but foudres work very well for mencía.”

Although some people might claim reduction as a fact of life when it comes to mencía, Dominique cautions against this. “It’s an error to associate reduction with identity,” he says. “Really, it’s a matter of soil management and viticulture, a matter of the variety, and making sure the grape is sufficiently nourished so that you don’t have to add anything during fermentation.”

But at the end of the day, when it’s subtle and in balance, reduction can add charm. “I like the touches of smoke, mocha, and flint that reduction can bring,” Dominique says. “I remember drinking Tempranillos from Ribera del Duero at the end of the ’90s that had that reductive note. It wasn’t super strong—it didn’t smell like animal—and it gave the wines aging capacity. That happens with mencía too. If it doesn’t smell like blood or meat or animal, and if it has that touch of smoke, I like it. I don’t look for it in my wines, but if the grape expresses itself that way, alongside the fruit, it can be something good.”