Tin Barn Vineyards | Amy Tsaykel

Fermentation: Making Big, Stinky Magic

In Uncategorized on 11/20/2009 at 2:30 am

Last week, the fermentation tanks were emptied. As shovels were heaved, vats were steamed, and juice flowed, our custom crush liaison Julia Iantosca took a moment to break down the mysterious, odiferous fermentation process for me. And, as usual, I raised all the questions you’re too embarrassed to ask!

Pretty juice, huh? What you can't see are the millions of unicellular fungi (yeast and other microbes) gobbling up nitrogen and ammonia. Nom!

What is Fermentation?

Sure, sure …. you know vaguely what it is.  But admit it: isn’t whole thing a little blurry? For anyone who didn’t pay quite enough attention in high school biology class , fermentation is the conversion of carbohydrates (such as sugar) into acid or alcohol.

What kicks off the whole process? Often it occurs naturally, with no prompting. But winemakers spur it on with yeast . The type of yeast used greatly influences the flavor of the wine. Once added, the yeast voraciously feeds on ammonia and nitrogen, converting the sugars in the grape juice into ethanol and carbon dioxide. When the carbon dioxide is released into the air, the alcohol remains.

(Will there be a test at the end? No, but you might enjoy regaling your friends with this newfound wine knowledge….)

Mike offers Corrugated Club members samples of fermenting Syrah.

What sorts of factors are monitored during fermentation?

Every day of fermentation, says Iantosca, a refractometer reading reveals the drop in sugar. Winemakers also keep close tabs on the temperature–a delicate matter.

In the insulated, stainless steel tanks in which most of our wine is produced, monitoring the temperature is as easy as looking at a gauge. For smaller batches, which are made in vats, it’s a little more complicated.

For the first several weeks of fermentation, the must (or juice) heats up pretty quickly. After the juice is transferred to another, more airtight containers , the warming process slows considerably. White wines are fermented to 64 to 68 °F, while red wines are ratcheted up to 85 to 90°F.

Is anything added to the juice during the fermentation process?

Obviously, yeast is added. But some winemakers also add highly artificial components to their wine. Tin Barn’s winemaker, Mike Lancaster, had always struck me as a purist, so I figured he’d shy away from extra chemicals and flavorings. The truth? Yes and no.

One basic chemical widely used in winemaking–and with good reason–is sulfur dioxide. This serves as microbial, as well as protection against oxygen contamination. This is especially important with white wines and pinot noirs, which are extremely delicate.

Winemakers might also might add yeast-based micronutrients that basically serve as a multivitamin for the fermenting juice. You can geek out over the different types of nutrients here.

So yes, there are definitely a couple of additives involved in Tin Barn’s winemaking process. But do we add artificial flavorings for contrived effects–to achieve, for example, the grapefruit character in our Sauvignon Blanc? Definitely not.

What can go wrong?

  • It’s imperative for the temperature to keep rising, lest stuck fermentation occur. And what is that? The whole process grinds to a screeching halt.
  • Another potential problem? Hydrogen sulfide can form, leading to the infamous rotten egg smell that proves ruinous to wine.
  • Grape juice is awfully attractive to spoilage organisms,  and without proper sanitation, batches are easily contaminated. “If only people knew how much of winemaking was janitorial,” says Iantosca, “they wouldn’t think it was quite so glamorous!”

More science, please?

If we’ve stoked your inner science fiend, you’ll be happy to know this is only the tip of the iceberg! Here are a few other sites you can visit to learn more about the fermentation process:

  • Vinquiry is a laboratory that conducts our testing and supplies much of our equipment.
  • Winemaker Magazine is a great resource for hobbyist winemakers and enthusiasts, or just curious drinkers
  • UC Davis Extension has a wide variety of winemaking courses, many of them online, for the truly insatiable wine geek.

Meanwhile, harvest is winding down, and we’re all thankful for another fruitful season. This Thanksgiving, I’ll most certainly raise a toast to all the hardworking people who put food and drink on our tables. And thus my  wine education continues …. because the best way to learn about wine is to drink it!


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