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Fermenting for Flavors
by Darryl Roberts
Magazine Issue: U.S. Vol. 2.3
f e r m e n t i n g f o r f l a v o r s
"Aromas of pineapples, apples and kiwi fruit, with complements of spice, butter, caramel, vanilla and toasty oak."

So reads another magazine's review of a chardonnay.

If you've ever had the chance to taste wine grape juice before it's been fermented, you know it doesn't taste like finished wine. It tastes like, well, grape juice. So where do all these fruit, spice and other flavors come from? (Do winemakers put them in?) Can they actually add different flavors to make wine taste a certain way? Well, the answer is yes, and no.

First, let's look at fruit flavors in wine. If winemakers don't add other fruits to wine -- and they don't -- then where do these fruit flavors come from? According to Terrance Leighton, molecular biologist at the University of California at Davis, "A wine's flavor, character and aroma are locked up in the grape, and it's the yeast (through fermentation) that activates -- unlocks -- these characteristics."

A wine grape is a unique fruit in that it contains natural chemical compounds that are also found in other fruits and vegetables. Fermentation, a simple chemical reaction, releases these compounds, and so we smell and taste these same aromas and flavors in the finished wine. For example, the strong black pepper aroma and flavor of California zinfandel (red, of course) comes from the same compound that gives black pepper its spicy kick. And the tangy apple flavor found in most chardonnays comes primarily from malic acid, the tart acid found in apples.

Let's take a quick look at the different winemaking steps and the flavors that winemakers can control.


Once the juice has been pressed from the grape, winemakers place it in a fermentation container (stainless steel tank, barrel, etc.). At this point they can either let the wild yeast (that came in on the grapes) do its thing or they can add cultured yeast. Different yeast strains create different flavors in wine. In chardonnay, for example, one strain may produce more tropical fruit flavors while another more citrusy ones. So winemakers can choose a cultured yeast strain that gives them the flavor profiles they want in the finished wine. Or they can let Mother Nature do her thing and take the flavors that she comes up with.


Secondary fermentation, also called malolactic fermentation (ML), usually produces flavors of butter and/or butterscotch. To make ML happen, the winemaker adds a strain of lactic bacteria to the wine, which converts the harsher malic acid -- the main acid in apples -- to lactic acid -- the acid found in dairy products. So, it's basically a conversion of a tart acid to a soft, creamy acid. A chemical by-product of this process is diacetyl, the component of butter that makes it smell and taste like, well, butter. So, if winemakers want a softer wine with buttery characteristics -- a chardonnay, for example -- they put some or all of it through malolactic fermentation.


Once fermentation is over and the sugar has turned into alcohol and other by-products, the yeast cells die (their food source is gone) or become dormant and fall to the bottom of the fermenter. Leaving white wines on their yeast sediment -- called lees, or, if you're French, lies -- for an extended period of time can produce pleasantly yeasty, pastry-like flavors. If you want to taste yeasty/leesy characteristics, try a "sur lie" chardonnay or sparkling wine or Champagne that has aged for three or more years in the bottle.


Oak barrels, depending on their age, oak type and toast level, contribute certain flavors to wine. For example, oak can impart clove, nutmeg, cinnamon, caramel, chocolate, coffee, vanilla and, of course, oak flavors. So winemakers will do what they call barrel trials to determine which type of oak barrel can best produce the flavors they want in their finished wine.

Knowing where the flavors of wine come from can help you understand why you may like one wine and not another -- and it can even help you decide whether you're going to like a wine before you even try it. Cheers!

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