Winemaker Jeff Cohn didn’t start out in the wine industry. In the 1980s he received an associate’s degree in culinary arts from Johnson & Wales University in Providence, R.I., and a bachelor’s degree in hospitality management from Florida International University in Miami. As he toiled in the hospitality industry, Cohn’s interest in wine increased.

After working for two years as an intern for Boordy Vineyards in Maryland during the early 1990s, Cohn knew that his future was in winemaking. He moved to California, earned a master’s degree in agriculture chemistry at Fresno State University and took a job as an enologist at Rosenblum Cellars in Alameda, where he was promoted to winemaker in 2000. Meanwhile, Cohn had started his own label, JC Cellars, in 1996, the same year he graduated from Fresno State. In 2006 he left Rosenblum to concentrate on JC Cellars in nearby Oakland, where he focuses on Zinfandel and Rhône-style wines. Cohn also consults for several California wineries including SummerWood in Paso Robles.

Wines & Vines: How do you select your yeasts for fermentation? Are you choosing them for flavor characteristics, grape variety or something else?

Jeff Cohn: I use about eight commercial yeasts—some years more. I select my yeasts by really getting to know each of the vineyards I work with. I try to highlight the positives of each vineyard and at times tone down certain aspects so other areas can shine more. Each vineyard I work with is a chance to bring out the best in flavors and aromatics. This process begins by tasting the vineyard as it starts to ripen and getting a better grasp of what it might present, almost like an artist and his palette of colors.

Let’s take the Zinfandel, for instance, from the Iron Hill Vineyard in Sonoma. The vineyard is in an amphitheater setting and planted on volcanic rock, not much dirt to speak of, with a very large lavender patch right next to the vineyard. This vineyard, planted with the Cooke selection of Zinfandel, produces a Zinfandel that is more in tune with the Northern Rhône than it is with Sonoma Zin. It has a very black/brick red color with aromatics of lavender, air-dried meats and black cherry, red and black cracked peppercorn and bittersweet chocolate. It has a core of minerality. This wine is always very lush in the front and mid-palate and is very focused on black cherry and chocolate-covered blueberry components and a burst of the iron minerality and dried meat characteristics once again. A very exotic style Zinfandel. To highlight the pepper components, I would use the D80 yeast from Scott Labs. To highlight the blueberry components and chocolates, I like to use Syrah yeast, and to highlight the black cherry and mineral aspects of this vineyard, I like to use RP15 (Rockpile yeast).

I also like to use many different sizes of fermentation vessels. For this particular vineyard, we will use half-ton bins and three-quarter-ton bins. I feel this process provides good cap management and a way to get the most out of this fruit. Each bin is inoculated with a different yeast, and I let one go indigenous.

The indigenous fermentation is always an experience. Sometimes they go fast, sometimes slower—and sometimes they may get very slow, and we need to re-inoculate to finish. But indigenous always adds another layer of aromatics and flavors to the program. It’s interesting as a puzzle piece.

I like to use Syrah, RP15 and native in four- to eight-ton tanks, whereas I use the other yeasts in half-, three-quarter and one-ton vessels. These decisions are made when I taste the fruit.

The yeasts do not need a specific temperature to get proper results—it is a matter of taste. I like warmer ferments for some fruit and cooler for others. I may use the same yeast for both cooler and hotter ferments. This will give me different results but also adds layers of complexity to the finished product.

Rockpile Ranch yeast isolated     Winemaker Jeff Cohn experiments with a lot of yeasts. About eight years ago he isolated a yeast from Rockpile Ranch vineyard in Sonoma County that subsequently became commercially available. "I was looking to work with Syrah yeast and do something special for JC Cellars," Cohn says. "With the help of Vinquiry, I was able to have my own liquid isolate." The yeast, now known as RP15, had a lot of benefits, Cohn adds. "First, it fermented up to 17º ethyl alcohol," he says. "Second, it highlighted black cherry aspects of fruit. Third, it really focused on the mineral aspects of all fruit. "Finally, it came from the Rockpile AVA. Many Zinfandel producers were looking for something new to try, and Rockpile Zinfandel was very popular at the time. Even though this yeast was isolated from Syrah, it was the perfect companion for Zinfandel." Lallemand, he says, put the yeast into dry format. It's now available through Scott Labs. L.D.

W&V: You’re using more concrete fermentors these days. How does that affect your yeast selection?

Cohn: I find yeasts that are more fruit-driven, like the Syrah yeast, are a better match than ones that are more mineral-driven. You do not need more vigorous yeast with cement. In fact, we usually get warmer ferments that hold out longer and go dry faster.

W&V: Do you use nutrients for your fermentations?

Cohn: I do use a selection of nutrients. I start the yeast up with Go-Ferm. The next day, if I see activity (a cap), I will add DAP. At 21º Brix, I will add Fermaid. This combination or cocktail of nutrients seems to do the trick and gets the wine to dryness.

W&V: Most of your wines have more than 15% alcohol. Do you ever have problems with wines that don’t ferment to dryness?

Cohn: Most of my wines are above 15%, and 95% of the time I do not have issues. But when I do, I re-inoculate with (Uvaferm) 43 or Fermachamp toward the end of fermentation. If I see I am having more dif ficulties, I add Williams-Selyem yeast, and this usually does the trick.

If I have put a slow-fermenting wine down to barrel, and I do not see enough activity, I will hit each barrel with 10ppm of SO2. This helps knock down acetics a touch and allows the yeast to keep going. We monitor the volatile acidity by either running it in the in-house lab or sending it out to a lab. We then make further decisions and may re-inoculate and stir the barrel to keep yeast suspended in the wine.

W&V: Did you face any additional difficulties with fermentations in the 2010 vintage?

Cohn: 2010 was a bear of a vintage for everyone, and I was not left out. I was fortunate that I was able to get all my fruit very ripe. That is, the fruit that came in. I lost all my Roussanne and Marsanne in Santa Barbara and all the Syrah in Santa Barbara. There was way too much rain and not enough sun. On the other hand, I lost two Zinfandel vineyards due to too much sun. Each of these vineyards went from 65º to about 116º in one day, early on in the season, before the fruit was ready for this type of heat. This spike bleached the fruit and then fried it.

Our biggest issues with fermentations in 2010 were that our fruit came in so late in the year and that it became so cold early on. Being in Oakland, the cool Bay Area, and the fact that my winery has no heating capacity, made certain fermentations sluggish. The ferments are taking a couple months longer to finish primary than I’d like. In the past I have found that many times when I have sluggish fermentations, the wines I produce have the highest levels of complexities, both aromatically and in flavors. What does not kill us makes us stronger, I guess.

A resident of the Santa Cruz Mountains, Laurie Daniel has been a journalist for more than 25 years. She has been writing about wine for publications for nearly 15 years and has been a Wines & Vines contributor since 2006.

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