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

How Winemaker's Know It's Harvest Time

Finally, Fall is just around the corner and harvest time is beginning. This is the point where grape growers and wine makers become very focused on the grapes as they ripen. Then, once the grapes reach just the right level of ripeness, they are quickly harvested because, unlike other fruits, grapes don't continue to ripen once picked. So, you have to get it right.

If the grapes are picked too early they can be too acidic, too tannic and not contain the proper amount of sugar for a full and proper fermentation. Conversely, if the grapes are picked too late, the sugar level will be too high which can lead to an overly sweet wine. This is because fermentation will only go to the point where the yeast naturally dies due to the level of alcohol in the wine. So, the “residual sugar” doesn’t get converted to alcohol and remains in the wine.

The bottom line for grape growers and winemakers is to find the perfect time for harvest. While there is some science and chemistry involved there is also a lot of experience and intuition that goes into the decision to harvest the grapes.

Here’s a quick overview of some of the signs that the grapes are ready for harvest:

The Visual Appearance of the Grapes

From the experience and intuition categories, winemakers look for the exact color of the grapes to know when to harvest. The grapes may also take on different textures and levels of shininess versus dustiness as they reach the proper ripeness.

The Visual Appearance of the Seed Color

Winemakers also look at the stems and seeds as a sign of ripeness. As the grapes ripen, the stems will turn from green to brown. An un-ripe grape will have seeds that are white or green. When the grape seeds turn brown, they are nearing time for harvest. Winemakers may also taste the seeds. Unripe seeds can be highly tannic and bitter.

The Taste of the Grapes

It might seem obvious, but the taste of the ripening grape will also yield telltale signs to the winemaker. The grapes will have gotten mostly through the tannic and bitter stage and moved into being sweet. But again, the experience of the winemaker will determine if the grapes have just the right amount of tart and tannic qualities (that are very important in winemaking) while also having just the right amount of sweetness.

The Brix Level

From the science and chemistry side of things, winemakers will use a device called a refractometer to measure the ripeness of individual grapes. Brix measures the sugar levels in the grapes and allow a winemaker to convert that to how much alcohol the finished wine will have.

The Feel of the Grapes

Ripe grape berries (the individual grapes) are generally easier to pull from the stalks.

So, these are the primary methods used by winemakers to determine when the grapes are ready for harvest. A bit of science and a whole lot of experience goes into the final harvest decision. Cheers!

The Fourth Fundamental Trait of a Good Wine - Sweetness

There are four fundamental traits that comprise a good wine and they all have to work together in balanced harmony. Previously we’ve explored Acidity, Tannin, and Alcohol . Let’s now take a look at Sweetness.

Sweetness in wine comes from natural grape sugars leftover after the fermentation has stopped. Or, by starting with overly-ripe grapes that produce a grape must which is so sweet that the yeast ultimately fails to convert all of it to alcohol. Perceived sweetness can also come from the alcohol itself, the toasted oak barrels used during aging, and simply from wines that are low in acidity.

The sugar that remains in wine is referred to as “residual sugar,” or RS, and is measured in grams per Liter (g/L). Here are the sweetness categories of wines:

• Bone Dry is 0-1 Grams/Liter (e.g., Brut Nature sparkling wines)

• Dry is 0-10 g/L (e.g., most red, white and rosé wines fall in this category, as do Brut & Extra Dry sparkling wines)

• Off-Dry is 10-35 g/L (e.g., Off-dry Riesling, Gewürztraminer, “Dry” sparkling wines)

• Medium-Sweet is 35-120 g/l (e.g., Madeira, Port, Moscato, Sweet Riesling)

• Sweet if the RS is greater than 120 g/L (e.g., Tawny Port, Late-Harvest wines, Cream Sherry)

  (Note: Coca-Cola has around 110 g/L)

In most wines, too much residual sugar results in a wine tasting sickly sweet. Conversely, if there’s absolutely no residual sugar, a wine may taste a bit harsh.

So, next time we’ll conclude this series by looking at how acidity, tannin, alcohol and sweetness must all be in balance in a really good wine. Until then, Cheers!