Can Yeast Affect the Final Flavor of a Wine?

I was recently in wine country and visited a favorite winery. While tasting some of the recent releases with the owner/winemaker, I posed the question “Does the type of yeast used affect the flavor of with wine?” The simple answer was “Yes!”

Yeast plays a critical role in the fermentation process, where it converts the sugars in the grape’s juice into alcohol and carbon dioxide. But, yeast can also produce a variety of other chemical compounds, including esters, phenols, and other aromatic molecules, that can definitely contribute to the wine's final flavor, its aroma, and even the way the wine feels in your mouth.

There’s also a difference between using cultured commercial yeast and wild yeast. This winemaker that I spoke to preferred to use the wild native yeast as a way to additionally differentiate their wine based on where it’s made (i.e., terrior) since it comes right from the environment - the grapes, winery, and the air.

Here are just a couple of ways yeast can influence wine flavor:

• Chemical Compounds Formed During Fermentation: These include things such as Esters and Aromatic compounds

• Fermentation Byproducts: There’s more that just alcohol that’s being produced in fermentation. Other byproducts such as acetaldehyde, sulfuric compounds and other volatile compounds

• Polysaccharides - These are long chains of sugar molecules that can make a wine feel smoother, creamier or softer in your mouth

So, simply put, Yes! The type of yeast is yet another variable in wine making. Wine making is an art, but there’s also a lot of science/chemistry that goes on too. Cheers!

The Art of Wine Making: Picking the Right Yeast for Fermentation

Natural Yeast on the Surface of Grapes

[Photo by Wayne Christensen on Unsplash]

Wine makers have used yeast for centuries to ferment the juice of grapes into wine. And, part of the art of winemaking is choosing the right yeast to use.

Wine makers have several choices in deciding which yeast to use to ferment their wine:

Wild or Native Yeasts - Grapes naturally have yeast on their skins (see photo). There are also natural yeast in the vineyard environment and yeasts that live within the winery. So, a wine maker can simply leave the crushed grapes and their juice to “spontaneously” being fermentation.

Advantages:

• Because wild yeasts are unique to each vineyard and winery, the add to the ‘terroir’ expression of the wine, making it even more unique

• Wild yeasts can produce unique chemical interactions that don’t occur with commercial yeasts

• Wild yeast is often viewed as more natural or pure

Disadvantages:

• It takes longer for fermentation to begin since the wine maker is relying on the yeasts in the air versus adding quantities of yeast directly

• Some natural yeast are not able to survive the rising levels of alcohol and die before fermentation is complete

• While also listed as an advantage, the unique flavors associated with natural yeast may result in undesirable results

Commercial Yeasts - This is the most common approach.

Advantages:

• Commercial yeasts are easy to purchase, transport and store.

• The fermentation process becomes more predictable and easier to control

• Some yeast will help reduce the volatile acids in the final product

• These yeasts will help to promote malolactic conversion

Disadvantages:

• Reduces a wine makers unique expression associated with native yeast

So, once again, choosing the ‘right’ yeast is just another part of a wine maker’s artistic expression. Cheers!

Think Wine is Just Grape Juice and Yeast. Think Again!

Photo by Roberta Sorge on Unsplash

What is more natural than a glass of wine?

Grow some grape vines, wait for them to produce grapes, harvest the grape bunches, de-stem them (sometimes), crush them to produce juice, leave the crushed grapes in contact with the juice to create color (in the case of red wines and rosé) and then rely on natural yeasts or added yeast to convert the natural sugars in the grape juice to alcohol and, voilà, - you have wine! It’s just that simple, right?

Well, wine isn’t always that simple. While some wines are indeed produced with these simple steps and ingredients, there are some other ingredients that can be used in the winemaking process. And, the only two ingredients that are required to appear on a wine label are the alcohol content and if it contains sulfites.

Here’s a few of the other ingredients that may be used in wine making or remain in a wine:

• Added Yeast Nutrients and Enzymes

  • Yeast nutrients are used to speed up the process of fermentation.

• Potassium Sorbate and Potassium Metabisultite

  • Both of these ingredients are used to guard against bacteria and protect the yeast from spoiling, and are commonly used together during the fermentation process to help the yeast ferment efficiently while improving the overall flavor.

• Acid, Sugar, and Tannin Additions

  • Adding acid will decrease the pH and increase the total acidity of the wine to ensure it is in overall balance

  • Adding sugar before or during fermentation can help boost the alcohol content. The process is called ‘chaptalization’ and also assists the yeast during the fermentation process.

  • Powdered tannins may be added early in the process to help add balance

• Acid Reducers

  • Calcium carbonate is used to reduce the acidity of the finished wine, and is sometimes added if the grapes have had trouble ripening. It’s usually added before or at the start of fermentation, so it doesn’t impact on the aroma of the wine.

  • Potassium Bicarbonate is also used to help lower the acidity

• Oak and Oak Chips, Powders, and Granules

  • Winemakers rely on oak barrels to flavor wine with notes of vanilla or subtle spices,

  • If the wine doesn’t come into direct contact with wood (i.e., stainless steel tanks), some producers will add oak chips, powders or staves to add oak flavors.

• Stabilizers and Anti-Sediment Additions

  • Potassium bitartrate is used as a seeding agent to promote tartrate precipitation during cold stabilization

  • Urease is added to reduce the level of urea in wines, when this is excessive, in order to avoid the formation of ethyl carbamate during aging.  The enzyme transforms urea into ammonia and carbon dioxide.

• Fining Agents

  • Fining agents are used for clarifying wine. These agents, such as bentonite (powdered clay), isinglass (fish bladder), casein (milk protein), gelatin or egg whites, combine with sediment particles and cause them to settle to the bottom of the vessel, where they can be easily removed before the wine is bottled.

• Grape Concentrate

  • Grape juice concentrate is sometimes included to boost the color of red wine and add a bit of sugar to smooth out the mouthfeel.

• Coloring Agents or Color Stabilizers

  • Coloring agents may be used to deepen the color of red wines, or to add ‘blush’ to whites

  • Stabilizers ensure the wine’s color does not change during fermentation and aging

• Dimethyl Di-carbonate, Ammonium Phosphate and Di-ammonium Phosphates

  • Dimethyl di-carbonate is used to stabilize wine by preventing microbial spoilage

  • Di-ammonium Phosphate is used to speed up the fermentation process

• Sulfur Dioxide

  • Usually listed as ‘sulfites’. It’s used to preserve the grapes and prevent oxidation during the winemaking process.

• Preservatives and Antibacterial Agents (e.g., potassium sorbate, dimethyl dicarbonate, sorbic acid, copper sulfate)

  • Preservative such as potassium sorbate or sorbic acid are used to 'stabilize' a wine and prevent a renewed fermentation by inhibiting the yeast cell from being able to multiply, grow and begin a new fermentation.

  • Dimethyl dicarbonate is used to stabilize the wine by preventing microbial spoilage

• Alcohol

  • Adding alcohol, usually from another grape-derived spirit such as brandy, is called fortification. Since yeast naturally dies at 15% ABV, addition of extra alcohol will push the alcohol concentration of a wine over the 15% mark.

  • Alcohol is added to “Fortified” wines such as Port, Sherry, Madeira, Marsala and Vermouth

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!

Wine Flavors From Fermentation

Wine's flavors come from the grapes, the fermentation process, and through aging. Last time we looked at the grapes that are the primary player in a wine's flavor. So, let's now explore how the fermentation process adds flavors to wine.

The only other ingredient in wine making, other than the grapes, is the yeast.  And, yes, yeast adds flavor. Just think of freshly baked bread.  Not that yeast makes wine taste like bread, but it certainly can impart flavor. Wine can be made from the natural yeast that forms on the skin of the grape, appearing as a white haze, as shown in the photo.  Or, winemakers can choose to use one of many strains of yeast that are produced in the laboratory in order to achieve the end result they are looking for.

The fermentation vessel also plays a role in a wine's flavor. Fermentation that is done in stainless steel tanks impart no flavor and allows the fruit flavors of the grapes to shine through. But, when fermentation is done in oak vessels the wine can take on woody flavors as well as flavors of spices, vanilla, and smokiness, as well as tannin that gives wine its mouth-drying, astringent, sensation.

Once fermentation is complete and the yeast has given its life for the production of alcohol, the yeast can either be immediately removed or the dead yeast (called lees) can be left in the fermentation vessel for some additional time to add yet additional flavor. This often adds a bit of bread-like aroma to the wine and makes for a richer mouth-feel of the final wine. Battonnage, or the stirring of the lees in the wine, can also enhance these flavors.

The fermentation process can also result in wines that are a bit sweet. Typically, the yeast will consume all the grape's natural sugar, turning it all to alcohol. But, if the fermentation is halted before all the natural sugar is consumed by the yeast, the wine will retain 'residual sugar' and be a bit sweet.

Oh, and by the way, the grapes, not just grape juice, can also play a role during fermentation. But, we'll leave that for next time. Until then, Cheers!