Chapter 1 - Wine Composition and Chemistry

Question 1

What are the major components of wine?

Answer 1

• 1. Water (~80-90%)
• 2. Alcohol
• 3. Acid
• 4. Sugar
• 5. Phenolic compounds

Question 2

What is wine?

Answer 2

The fermented product of grapes.

Question 3

What is the most prevalent ingredient in wine after water?

Answer 3

Alcohol. which is usually 10%-15% of the volume, although some contain more or less. Ethyl alcohol (ethanol) is the primary result of alcoholic fermentation and the main alcohol component of wine. Other types of alcohol are glycerol and methyl alcohol.

Question 4

What’s one element that contributes to the mouth-filling, tactile sensation of a wine as it rests on the palate? And what is it referred to?

Answer 4

Alcohol content is one element that contributes to the mouth-filling, tactile sensation of a wine on the palate - it’s often referred to as a wine’s “weight” or “body” …

Higher levels of alcohol = tend to be heavier in weight than wines with lower levels of alcohol

Question 5

____ levels of alcohol can also result in slow, thick-appearing “tears” or “legs”

Answer 5

High levels of alcohol can also result in slow, thick-appearing “tears” or “legs”

Question 6

Acids usually make up between .5% and 0.75% of a wine’s volume. There are 7 acids present in wine. Name the most common one.

Answer 6

1. Tartaric acid - wine diamonds. Most prevalent acid found in grapes and wines, unique propensity to form solid crystals or tartrates (“wine diamonds”) at low temperatures. Once it takes this form it will not redissolve into the liquid and the wine will become noticeably less acidic.

Question 7

This is a sharp tasting acid frequently associated with green apples. What’s it called?

Answer 7

2. Malic acid - Underripe grapes and cool climate grapes are typically high in malic acid. However, the level of malic acid decreases during the ripening phase of the grape on the vine. Wines made from overripe grapes or grapes grown in hot climates tend to have low levels of this acid. High levels of malic acid can be assuaged using the winemaking technique known as malolactic fermentation.

Malic acid is found in nearly every fruit and berry plant, but is most often associated with green (unripe) apples, the flavor it most readily projects in wine. Its name comes from the Latin malum meaning “apple”.

Its chemical structure allows it to participate in enzymatic reactions that transport energy throughout the vine.

Its concentration varies depending on the grape variety, with some varieties, such as Barbera, Carignan and Sylvaner, being naturally disposed to high levels. The levels of malic acid in grape berries are at their peak just before veraison, when they can be found in concentrations as high as 20 g/L. As the vine progresses through the ripening stage, malic acid is metabolized in the process of respiration, and by harvest, its concentration could be as low as 1 to 9 g/L. The respiratory loss of malic acid is more pronounced in warmer climates. When all the malic acid is used up in the grape, it is considered “over-ripe” or senescent.

Question 8

What is malolactic fermentation?

Answer 8

Malolactic conversion (also known as malolactic fermentation or MLF) is a process in winemaking in which tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation is most often performed as a secondary fermentation shortly after the end of the primary fermentation, but can sometimes run concurrently with it. The process is standard for most red wine production and common for some white grape varieties such as Chardonnay, where it can impart a “buttery” flavor from diacetyl, a byproduct of the reaction.[1]

The fermentation reaction is undertaken by the family of lactic acid bacteria (LAB); Oenococcus oeni, and various species of Lactobacillus and Pediococcus. Chemically, malolactic fermentation is a decarboxylation, which means carbon dioxide is liberated in the process.[2][3]

The primary function of all these bacteria is to convert L-malic acid, one of the two major grape acids found in wine, to another type of acid, L+ lactic acid. This can occur naturally. However, in commercial winemaking, malolactic conversion typically is initiated by an inoculation of desirable bacteria, usually O. oeni. This prevents undesirable bacterial strains from producing “off” flavors. Conversely, commercial winemakers actively prevent malolactic conversion when it is not desired, such as with fruity and floral white grape varieties such as Riesling and Gewürztraminer, to maintain a more tart or acidic profile in the finished wine.[4][5]

Malolactic fermentation tends to create a rounder, fuller mouthfeel. Malic acid is typically associated with the taste of green apples, while lactic acid is richer and more buttery tasting. Grapes produced in cool regions tend to be high in acidity, much of which comes from the contribution of malic acid. Malolactic fermentation generally enhances the body and flavor persistence of wine, producing wines of greater palate softness.

Question 9

This third acid is not usually a component of grapes, as it exists in such minute quantities a specialized equipment is required to measure it.

Answer 9

3. Citric acid. Its minute presence has no sensory impact on the majority of wines. Sometimes it’s added to increase the total acidity of a wine.

Question 10

This acid isn’t found in grapes at all but is created by a bacteria…This is 1 of 3 fermentation acids.

Answer 10

Lactic acid bacteria - winemakers convert malic acid into lactic acid through malolactic fermentation. This acid is < less intensely acidic than malic acid, so wines that undergo MLF tend to be softer and smoother in mouthfeel than those that do not. This also provides wine with a creamy texture and in some cases, a buttery aroma (diacetyl). Lactic acid is also created during primary fermentation in very small amounts.

Question 11

What’s the second type of fermentation acid?

Answer 11

Acetic acid is found in most types of vinegar. A low level of acetic acid is typically created during fermentation. Acetic acid, unlike other acids here in winemaking, is volatile, so it readily evaporates and joins the aromas of the wine, adding to the complexity of a wine’s bouquet, particularly in red wines.

However, in higher concentrations, this acid can be unpleasant and make a wine undrinkable, typically a result of a chemical reaction between ethanol and oxygen caused by harmful-to-wine-bacteria acetobacter.

Technically, the threshold for detecting acetic acid in wine is around 700 mg/L; over this threshold the wine becomes objectionable, and anything over 2.0 g/L is considered spoiled as the wine will taste, well, like vinegar. To self diagnose the presence of acetic acid in your wine, look for a distinctive aroma of vinegar, and if you detect a smell of glue or nail polish remover, that’s ethyl acetate, which is the next stage of acetic acid spoilage and the wine is lost.

Question 12

The third fermentation acid in wine is…

Answer 12

Succinic acid. A minor component in grapes and a by-product of normal alcoholic fermentation. It has a sharp, slightly bitter, slightly salty taste.

Question 13

Like citiric acid, this acid is a minor component in grapes…and a by-product of the alcoholic fermentation process, too…

Answer 13

Succinic acid.

Question 14

What are the two numbers used to describe the acidity level of a wine?

Answer 14

Total Acidity = which is the volume of all the acids in a wine

and

pH = the level that represents the combined strengths of the acids present. Wine usually measures between 2.9 and 3.9 on the pH scale.

Lower # indicates stronger acid content.

Question 15

What sugars make up a grape?

Answer 15

Nearly equal amounts of glucose and fructose. Grapes typically contain 15%-28% sugar at harvest!

Question 16

What’s special about glucose and fructose for winemakers?

Answer 16

They are both highly fermentable monosaccharides, simple sugars. During fermentation, given the right conditions, the yeast will convert these sugars into ethanol, turning grape juice into wine.

Residual sugar can add some weight or “body” to wine in the form of tears, thick and slow appearing when a glass is swirled.

Question 17

Wine has phenolic compounds. Name the 5 major compounds (polyphenols, phenolics, various molecules present in wine)….

Answer 17

1. Anthocyanins - This gives red wine its color…the color of a red wine is influenced by the amount of anthocyanins and the acidity level of the wine. The more acidic wines appear redder in hue while less acidic ones appear blue in hue.
2. Flavonols (flavone) - Yellow pigment found in white wines, some with more sun exposure yield golden pigments.
3. Tannins! - Astringent, bitter compounds found in the skins, seeds, and stems of grapes. Also found in oak and oak barrels. Tannins form the structure of ‘backbone’ of big red wines and are a natural preservative and help protect red wines from oxidation during the aging process. When present in wine, tannins are easily detectable by the textural drying sensation they produce in the mouth.
4. Vanillin - an aromatic compound in oak that imparts a vanilla scent to barrel-aged wines. The compound in oak barrels is the same found in vanilla beans.
5. Reservatrol - Antioxidant, healthy benefits…the phenolics of a grape are concentrated primarily in the skin and seeds. Because of this, red wines which are fermented in contact with the grape solids, are much richer in phenolic compounds than white wines.

Question 18

Why are tannins so important in wine?

Answer 18

Tannins bind to proteins in your saliva, causing a drying sensation on the palate. They contribute to the texture or feel of a wine in the mouth and can also have a bitter taste.

Astringent, bitter compounds found in the skins, seeds, and stems of grapes. Also found in oak and oak barrels. Tannins form the structure of ‘backbone’ of big red wines and are a natural preservative and help protect red wines from oxidation during the aging process. When present in wine, tannins are easily detectable by the textural drying sensation they produce in the mouth.

Question 19

What are aldehydes?

Answer 19

Aldehydes are oxidized alcohols that are formed when wine is exposed to air. Acetaldehyde can impart odours described as ‘over-ripe bruised apples’, ‘stuck ferment’ character or ‘sherry’ and ‘nut-like’ characters.

Some wines such as sherry and Madeira are made using techniques that encourage the formation of aldehydes, but any wine will take on an oxidized or “maderized” character if it has been exposed to excessive oxygen during production or storage. Wines also become oxidized after being open too long or exposed to heat.

The most common aldehyde in wine is acetaldehyde, which is formed by the oxidization of ethanol. Acetaldehyde is what gives fino sherries they distinctive aromas.

Fino is a dry white wine made from palomino grapes, which, as is the case with Manzanilla, is aged under a layer of yeasts which make up the veil of flor.

“By Eric Asimov
Dec. 3, 2015
I regard every wine we try as a treat. But our next wine is one that I especially love: fino sherry from Jerez de la Frontera in the Andalusia region of southern Spain. It is completely different in several ways from any of the wines we’ve examined before.

Most obviously, fino is fortified, which means that neutral spirits are added to the wine. In the case of fino, it is barely fortified and only to bring up the alcohol level of the still wine to 15 percent, the minimum level for fino.

Why fortify it at all? This is a question that the sherry region may grapple with in the near future. Other fortified wines, even other sherries, have clearer reasons for fortification.

Oloroso sherries are fortified up to 17 or 18 percent to kill any trace of flor, the layer of yeast that gives fino sherries their character (another distinction from other wines) but which oloroso does not need.

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Port is fortified up to 20 percent or so, with the purpose of halting fermentation before all sugar is converted into alcohol, leaving port sweet.

But fino? Long ago, the reason may have been to stabilize the wine for travel, and up until about 40 years ago, most finos were fortified to around 17 percent alcohol. But today, the reasons aren’t obvious. It’s certainly not to keep fino sweet. Fino is blissfully bone dry.

Despite the alcohol level, good fino is delicate in texture and great with food. It should never feel heavy, and the best finos are complex and refreshing. Manzanilla is a particular form of fino sherry produced only in the seaside town of Sanlúcar de Barrameda, where it develops a tangy sea-salt aroma and a texture that’s almost fragile compared with other finos.

For our purposes, though, we will concentrate only on Jerez finos, though with a departure from our routine. One stylistic issue in Jerez today revolves around filtration. Most mass-market finos today are heavily filtered, often to the point where character, texture and flavor are stripped out. As a result, many good producers today are also offering small lots of finos “en rama,” indicating that the wines are lightly filtered at most. This gives us the ability to contrast the same wine in its standard form with an en rama version.”

Question 20

What are esters?

Answer 20

Esters are molecules that result for the joining of an acid and an alcohol. They represent the largest group of odiferous compounds in wine. Most are desirable at low concentrations but some are considered off-odors at high enough concentrations.

At low concentrations that can impart a fruity, banana, flowery aroma. Too high they can smell like varnish, nail polish remover, or glue…

Question 21

What gives sparkling wines its bubbles or still wines some petillance with a pour?

Answer 21

CO2 Carbon Dioxide

Question 22

Sulfur and sulfites have what role in wine?

Answer 22

Sulfur is an important preservative that is widely used to keep wines stable after fermentation. Sulfur is also produced in minute quantities as a natural by product of fermentation. Therefore, all wines contain at least trace amounts of sulfites even if no sulfur is added during winemaking.

As sulfur is an antioxidant and antibacterial agent, producing wine without the addition of sulfur is very challenging.

Some people are extremely sensitive to sulfur…so wines destined for interstate commerce in the US for example that contain more than 10 parts per million of sulfur dioxide are required to display ‘contain sulfites’ on the warning label.