Heat is the new hot topic in winemaking. After decades of relative obscurity, interest in thermovinification—heating grapes and must to near-boiling temperatures prior to fermentation—is simmering nicely in California wine circles. Fans of pre-heating say it does wonders for color and tannin extraction, and with the most advanced technological bells and whistles, allows for essentially deconstructing and reconstructing grape chemistry: Maximize the good stuff, blow off the bad stuff.

Leaving aside how well this approach goes over among adherents of “natural wine” (you guessed it, not very well), thermo raises some of the same questions that hover around another temperature strategy: cold soaks. Winemakers and enology researchers have argued for years about whether letting red grape skins bathe in their juices for a few days before fermentation kicks in really accomplishes anything, or if it simply pulls out some color and other goodies early in the game that would show up eventually anyway. On the hot front, what do we know so far?

Primer on heat
Thermovinification in various forms has been around for decades, most prominently in Europe. Various combinations of equipment, temperatures and times have been used to accomplish a number of things, most frequently upping the extraction of color and tannin from grapes relatively deficient in one or the other. Burgundy and the Rhône have been major players, with frequently color-shy Pinot Noir and Grenache getting the treatment. Some bulk white wines have utilized thermo as well, in an attempt to get the most out of over-cropped fruit. Applying heat also inhibits troublesome enzymes such as polyphenol oxidase and laccase.

Some producers have taken advantage of heat’s value as a sanitizing agent: Chateau Beaucastel in Chateauneuf-du-Pape, for example, has heated red grapes for years in an attempt to beat back Brettanomyces—evidently, according to many tasters, with mixed results.

Winemaker Eric Laumann at the Monterey Wine Co., a custom-crush facility that uses several thermo techniques, says the most basic approach warms crushed grapes with a heat exchange column, up to about 140ºF for anywhere from one to 24 hours. There are also horizontal macerators, somewhat like rotary fermentors, which employ heating elements and paddles to heat the grapes to about 125ºF for 24-48 hours. Both of these methods aid with color and tannin extraction, and as a side benefit, they can volatilize and disperse certain unwanted compounds such as pyrazines in under-ripe or cool-climate Bordeaux varieties.

The newest top-end technology, known as Flash-Détente, goes one better, briefly heating the grapes to 185ºF, then cooling them in a vacuum. The water in the skins and pulp, brought nearly to boiling, blows the grapes to smithereens in the vacuum, literally taking them apart cell wall by cell wall, releasing numerous compounds in the process. The sound of this step, Laumann says, is a lot like a popcorn popper, and he figures the noise is caused by seeds hitting the wall. Flash-Détente also captures the vaporized water and volatilized compounds and chills them in a condenser column, allowing them to be blended back in if winemakers desire.

Exactly what goes on with which compounds at what temperatures is still a matter of conjecture. Laumann and Monterey Wine Co. are working with researchers at the University of California, Davis, to get into the details; Doug Adams will be looking at concentrations of various phenolics at various stages in the Flash-Détente process, and Linda Bisson and Kay Bogart will be examining the rise and fall of numerous flavor and aroma compounds.

What we know so far
We know for sure that heat—especially high heat—breaks down cell structure all by itself, without the benefit of yeast or ethanol, and that helps release many of the goodies we want in our wines. Standard red fermentations spend time in the 80º-90º range, sometimes higher, since yeast and ethanol by themselves won’t get the job done. Thermo does this breakdown job earlier and better.

There are other methods for dealing with rogue enzymes, and other ways of removing or reducing pyrazines, so the major payoff of thermovinification for reds would seem to be the heightened extraction of color and tannin. For California winemaking, one would have to ask, is this a big problem? Is lack of extraction—or for that matter, underripe fruit—a perennial issue with California reds? Wouldn’t it be better to design a machine that extracted finesse?

Getting color and tannin out early does, however, give winemakers some extra options, like fermenting at cooler temperatures, using different yeast strains and doing red wine barrel fermentation simply with liquid juice that already has its cargo of pigment and tannins, not with messy grapes. So, there may be some openings for finesse.

And it may be that that pulling out phenolics with heat and water does something different from extraction with ethanol. Thermo seems to stabilize the blue forms of anthocyanins, keeping them tied to the red forms, giving more purple color in the wine. Winemakers like Scott Rich at Talisman, who did his master’s thesis at Davis on fermentation temperature, think that “good” tannins (softer, rounder) might come out with just water and heat, while more of the “not so good” (harsher) ones might come out with ethanol as a solvent. Doug Adams will be looking at the numbers for anthocyanins, tannins and iron-reactive phenolics at stages from grapes to wine on heat-treated fruit.

More intriguing to me than the phenolics are all the aroma and flavor compounds that may get unleashed, blown off, or otherwise transmogrified by high heat. Linda Bisson notes that high heat can certainly volatize several categories of compounds: pyrazines to be sure, but also terpenes and thiols. (With Flash-Détente’s cooling column, perhaps these things could be put back in.) Many aromatic compounds or their precursors are not volatile but instead initially bound to sugar in glycoside forms, only getting pried loose by yeast activity; extreme heat pries them loose from the get-go, making them more available earlier, which may or may not be a good thing.

Based largely on tasting at this point, Bisson and Bogart think thermo gives a big boost to fruity and especially berry components, making them quite intense early in the life of a wine, rather than being doled out slowly over time after standard fermentation. Exactly what these compounds are isn’t known (that’s part of what they will be researching), but some of Bisson’s candidates are generic fruity esters—maybe lactones, maybe the fruity as opposed to floral noriseprenoids. Whatever the mix, her initial hit is that heat results in wines that are more intensely berryish but less complex.

Cooking varietal character?
These chemical hunches dovetail with reports from a number of sources that thermovinification can make for very good, sound, solid wine, but at the expense of varietal character. Pumping up the fruit and burning off the rough edges can have a downside in the loss of distinctiveness.

I called Bob Kreisher at Mavrik North America, one of the firms specializing in fixing up problem wines by removing VA, smoke taint, excess alcohol and the like. I had noticed that thermovinification wasn’t in their list of wine treatments, and Kreisher says the omission is deliberate: They looked at the technology and decided they weren’t fond of what it could accomplish. “It has everything to do,” he says, “with the commodification of wine; it enhances fruit character, mostly by eliminating everything else.” He thinks the role of this technology ultimately resides in high-output winemaking.

I was lucky enough to spend time at two important Italian wineries this spring, and I checked back in with them for their thoughts about thermo. At Arnoldo Caprai in Umbria, the flagship wine is a full-throated Sagrantino, a local variety that arrives in the bottle with an unmatched tannic wallop that takes a decade or more to resolve beautifully. Since winemaker Marco Caprai does everything he can to encourage tannin extraction, I thought he might be a thermo fan; but no, the winery believes that it gets in the way of the varietal character of their prized variety.

Frescobaldi and its many estates in Tuscany was the other stop on this trip, and there I learned that the use of thermo had become an important part of not only their Pinot Noir production, but their Sangiovese winemaking as well. When I checked back via e-mail for more details for this article, I asked what they thought about those who claim that thermovinification reduces varietal character. “They are right,” responded Marquis Lamberto Frescobaldi. “It can only be used in small percentages.”

This isn’t a bad thing; technology that improves one component of a wine blend can be quite valuable, as in the contributions of a small proportion of barrel-fermented white wine in a mostly tank-fermented cuvée. Eric Laumann at Monterey Wine Co. might well agree that the Flash-Détente system he is so fond of is a great way to add another layer to a wine, without being the universal option for all wines.

This fancier version of thermo technology isn’t cheap; the Monterey Wine Co. setup cost roughly $2 million. But if it fills a number of niches—from removing pyrazines to enhancing purple tones, from denaturing enzymes to widening fermentation choices — it could earn its keep in custom-crush and large-production settings.

And during the next couple years, we’re going to find out.

Tim Patterson is the author of the upcoming Home Winemaking for Dummies. He writes about wine and makes his own in Berkeley, Calif. Years of experience as a journalist, combined with a contrarian streak, make him interested in getting to the bottom of wine stories, casting a critical eye on conventional wisdom in the process. To comment on this article, e-mail edit@winesandvines.com.

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