Ever Wonder? How is Wine Made? Part 2

Last time we began looking at the wine making process, starting with the grapes. While the grapes certainly are the most important ingredient in wine making, there is another very important ingredient - yeast. So, let’s take a look at the fermentation process.

Once the grapes are harvested and prepared for the wine making process, it time to turn the grape juice to wine. Large tanks are used in this process and here is where yeast is added.  It's the natural sugar in the juice of the grape that gets consumed by the live yeast. The bi-product of the yeast's consumption of sugar is alcohol and carbon dioxide (CO2).  Remember that red wines have the juice and skins together in the fermentation tank and the production of CO2 causes all the skins to float to the top of the tank.  So winemaker's have to periodically 'punch down' the skins to intermix them with the juice or 'pump over' the juice as another means of keeping the skins mixed in with the juice. But regardless of the grape type, the fermentation process is relative quick, lasting typically from ten days to two weeks. And, another factor limiting the fermentation time is the life of the yeast. Depending on the strain of yeast, the fermentation process will stop once the alcohol level reaches levels of 16-18% when the yeast dies or after all the sugar is consumed.

Once fermentation is complete, white wines will be transferred to stainless steel tanks or oak barrels for aging. Red wine will then be separated from the skins and moved to vessels for aging. And, that’s where we’ll pick up next time - aging of wine. Cheers!

Fermentation Vessels Can Affect the Flavors of a Wine

In a recent blog, I listed some of the many factors that can affect a wine’s flavors. One of the factors is the type of vessel chosen by the winemaker to ferment the wine. So, let’s take a closer look.

The three most common fermentation vessels are made of either oak, stainless steel or concrete. Each of these can affect the flavor of the wine due to the degree to which the wine is exposed to oxygen.

Fermentation in Oak 
Oak fermentation barrels allow for the gradual influx of oxygen which helps to softened tannins and acid while developing a ‘rounder’ more balanced wine. Oak itself also imparts flavors. French oak is known to yield more subtle flavors like clove and spice to a wine while creating a silkier, smoother mouthfeel, while American oak typically imparts aromas of vanilla and coconut. And, the degree to which these flavors are imparted varies by the level of ‘toast’ created on the barrel during its production. So, for instance, a barrel with a ‘medium’ toast will impart less flavors than a barrel with a heavy toast. Finally, once an oak barrel has been used three to four times, the majority of the flavors have been extracted and it becomes a ‘neutral’ barrel that imparts little to no flavors.

Fermentation in Stainless Steel

Unlike oak, stainless steel fermentation vessels can be tightly sealed so as to allow little to no oxygen exposure of the wine during the fermentation process. And, a winemaker may fill the top of the tank (the headspace) with inert gas to drive out all of the oxygen. This makes for brighter, fresher fruit-forward wines. The stainless steel imparts no flavor characteristics to the wine. Stainless steel tanks are also used because they offer optimal refrigeration capabilities when a winemaker wants to cold-ferment the wine.

Fermentation in Concrete

Concrete-type vessels have been used to ferment wine for as long as wine has been made. Concrete tanks can be open for oxygen exposure, or sealed like stainless steel to avoid oxygen. The concrete itself is quite neutral so it doesn’t impart significant flavors like oak, but it can add mineral-like flavors to the wine.

Ever Wonder? How Does Temperature Affect Wine Fermentation

There’s a lot of chemistry that goes into making wine. And we learn from basic chemistry that heat is a catalyst. When heat is applied to a chemical reaction, it speeds things up. So, temperature plays a role in the fermentation of wine.

The higher the fermentation temperature the faster the yeast will convert the grape’s natural sugars to alcohol. But, winemaking is a slow process. From the growing of the grapes to the aging of the wine. And, fermentation is no exception. Winemakers don’t want to rush this process. So, they actually take steps to cool-down, the thus slow-down, the fermentation process.

If a wine is fermented at too high a temperature, it can lack character as well as remove any terroir that the winemaker was hoping to capture. By fermenting a lower temperatures, a winemaker preserves the fruit flavors and helps preserve the subtle elements that terroir can add.

Red wines are typically fermented between 70 and 85 degrees F (20-30 degrees C). This temperature range results is richer colors, good tannin levels and richer fruit flavors. Fermentation temperatures that approach 90 degrees F can result in “cooked” flavors making the wine taste stewed, prune-like or raisin-y.

White wines are typically fermented even cooler than red wines at temperatures between 45 and 60 degrees F (7-16 degrees C). This helps preserve a white wine’s bright fruit aromas and flavors while providing balanced acidity levels.

Ever Wonder Where Fruit Aromas & Flavors Come From in Wines?

When I first became interested in wines, I remember asking if other fruits were used in the production of wines. After all, so many wines smell and taste like a lot of fruits other than grapes. So, if grapes are the only fruits used in wine making, how do all those other aromas and flavors get into the wine?

Well, it turns out that there’s a lot going on during fermentation, not just the yeast converting the grape’s natural sugar to alcohol. There are also chemical reactions going on that create hundreds of aroma and flavor compounds. Wow!

These “compounds” are identical to the compounds that we already associate with smells and tastes. So, when you smell a fruit aroma in wine you are smelling the same aroma compounds that also naturally occur in those fruits. The same is true with flavors.

Other aromas such as vanilla, tobacco, leather, coffee, caramel and toast come from the oak aging of the wines. Depending on the amount of ‘toasting’ the barrel undergoes affects the range and depth of these aromas.

So next time you have a glass of wine take time to smell it in the glass before you sip. You’ll be amazed to discover the aromas of dark fruits in red wines such as berries and plums while white wines can have aromas of apples, pears, melons and citrus. And then sip the wine and enjoy all the fruit flavors it has to offer. Cheers!

Wine Flavors from Fermentation - Part 2

So far, we've learned that wine gets it flavor from three things - the grapes, fermentation and aging. Last time we looked at the fermentation process and how the yeast can affect flavor. But before we move on to flavors associated with aging, let's take a step back to the first item that affects a wine's flavor - the grapes.

While the juice of the grape plays a leading role in the flavors of a wine, the other parts of a grape also can play a supporting role. Items such as the stems from the bunch of grapes, the grape skins and the seeds.

These grape solids are all potential modifiers of the finished wine's flavor. These grape solids contain tannins, proteins and other microscopic solids that can benefit the final product. But, other solids such as leaves, sticks from the grape vine and dirt are undesirable solids that are always removed (For reference, these undesirable items are often referred to as MOG: Materials Other than Grapes.)

With respect to the stems that the grapes were grown on, winemakers can decide if they want to de-stem the grapes before the wine making process begins.  White wines are usually made from de-stemmed grapes. But, a red wine’s tannin is increased by leaving some or all of the stems in the juice.

Grape skins also contain flavor compounds. And, just like brewing a cup of tea, the longer you leave the grape skins in contact with the juice, the bolder the flavors can become. The depth of color of a wine also comes from the length of time the wine is left in contact with the skins.  For example, if you remove the skins immediately, no color is imparted to the wine.  The best example of this is Champagne, a sparkling white wine, that is produced from Chardonnay grapes (a white wine grape), and Pinot Noir grapes and Pinot Meunier grapes that are both red wine grapes. Another example is rosé wines that are made from red wine grapes that see very little skin contact time after pressing resulting in the light pink color.

The grape seeds will also play a role in the wine's flavor as it ferments because they too contain tannin that adds structure and makes wines better able to be aged.

So, it's not just the juice from the grape that affect the flavor of the wine. These other solids play a very important role.

Next time we'll take a look at the final process that affects a wine's flavor, the aging process.

Until then, Cheers!