Chapter 16

Wine Faults and Flaws

Wine Aroma and Flavor Descriptors

Bareroot, Turnip, Earth

Geosmin may be produced by molds growing in the winery environment which has aromas of beetroot, turnip, and earth. If present as a volatile compound in the winery environment it may contaminate the wine.

Barnyard-Like, Horsey, or Horse Blanket

Brettanomyces spp. (colloquially known as Brett) are yeasts that cause a wine defects described as barnyardlike, horsey, horse blanket, wet dog, tar, tobacco, cheesy, creosote, leathery, pharmaceutical, and even mousy. The main compound responsible for imparting the farmyard or manure aroma is 4-ethylphenol (4-EP).

Prevention and Treatment

Brettanomyces contamination is often a result of careless winemaking and, particularly, poor hygiene management. Oak barrels can become impregnated with Brettanomyces and thus contaminate wine during maturation. Indeed, whole cellars can be contaminated, a situation that is very difficult to rectify.

Bitterness or Astringency

Bitterness can be from excessive phenolics from highpressure pressing, prolonged pressing, rough handling of grapes and must. Excess contact of juice/fermenting wine with stalks, seeds, leaf material as well as higher fermentation temperatures increase phenolic extraction.


Diacetyl (2,3-butanedione) can be produced by both yeast and bacteria, and at low levels (1-4mg/L) can add complexity to a wine by imparting buttery or butterscotch characters. At high levels (greater than 5mg/L) the aroma might be considered objectionable (excessive buttery), such that the wine might be regarded as defective.


The volatile phenol 4-ethylguaiacol (4-EG) is the major spoilage compound associated with the growth of Brettanomyces yeast in wine.

Cork Taint

The phenomenon of cork taint, or corkiness as it is sometimes called, is characterized by a moldy/must offflavor. This is an unmistakable musty smell resembling fungus or autumnal woodlands and renders the wine undrinkable although still harmless.

Prevention and Treatment

Never use chlorine in the winery environment and screen incoming cork lots. Prevention is the best treatment because TCA is impossible to remove.

Fatty Mouthfeel

Ropiness is manifested as an increase in viscosity and a slimy or fatty mouthfeel of a wine. In France the fault is known as graisse, which translates to fat.


All wines carry a certain amount of dissolved carbon dioxide throughout their early lives and usually have lost it all or at least what's perceptible by the time they've been moved around the winery, stored in barrels, racked, and bottled.


Geranium aroma is an odor reminiscent of crushed geranium leaves. This taint may be caused when sorbic acid has been added to red wine to inhibit fermentation activity by Saccharomyces.

Green Bell Pepper

IBMP (2-lsobuty1-3-methoxypyrazine) is the main compound responsible for the green bell pepper aroma in wine. Common descriptors include, grassy, bell pepper, herbal, and leafy and these types of characters have been deemed to contribute to varietal character in Sauvignon Blanc. In red wines however, this flavor is largely unpopular.

Green Flavors

Green, vegetal flavors in wine are typically associated with fruit that has not achieved the desired level of ripeness. Often such wines suffer from other quality issues linked to grape immaturity, including high acidity, poor color, and lack of varietal aroma. The main compounds eliciting green/vegetal flavors in wine are methoxypyrazines (also known as MPs), green leaf volatiles, and some thiols with MPs being the most important (Pickering, 2018).

Prevention and Treatment

Destemming is critical, as the presence of stems during vinification significantly increases wine MP concentration. Minimizing skin contact pre-fermentation is very important to reduce the potential for green wines given the high level of MPs are located in the grape skin. Thus, crushing should be avoided where possible.


Although mousy off-flavor occurs infrequently in wine, it can be economically disastrous to the wine producer as, at worst, it can render the wine unpalatable or, at best, decrease the quality of the wine resulting in a lower sale price. Wines infected with either lactic acid bacteria (LAB) or Brettanomyces yeast can potentially produce mousy off-flavor. There are three known compounds that cause mousy off-flavor: 2-ethyltetrahydropyridine, 2-acetyltetrahydopyridine, and 2-acetylpyrroline.

Nail Polish, Solvent, Glue

Ethyl acetate is recognizable on the nose as a smell of nail polish, solvent, or glue. Ethyl acetate occurs when ethanol reacts with acetic acid. Factors that can influence ethyl acetate formation include the yeast strain, fermentation temperature, the amino nitrogen content of the juice, and sulfur dioxide levels.

Phenolic, Medicinal, Pharmaceutical

The volatile phenol 4-ethylphenol (4-EP) is the major spoilage compound associated with the growth of Brettanomyces yeast in wine.

Sherry, Cut Apples, Nuts

Acetaldehyde is the most important and familiar sensory aldehyde in wine and constitutes about 90 percent of the total aldehyde content. At low concentrations it can impart a fruity flavor to wine, which often occur in freshly fermented wine.

Prevention and Treatment

Practicing effective sanitation in the cellar, excluding oxygen from the wines and maintaining adequate levels of free sulfur dioxide will go a long way to preventing acetaldehyde formation.

Smoke Taint

Smoke taint occurs in the vineyard by wildfires which exposes wine grapes to high levels of smoke, thereby conferring undesirable characters to wine (Figure 16.6). These wines convey strong ashy, burnt, and smoky aromas, with an excessively drying back-palate and retro-nasal ash perception, usually described as smoke tainted. The consequence is a significantly reduced market value, as consumers have been shown to reject smoke-tainted wines. Of all of the compounds present in smoke, the volatile phenols guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol, eugenol, o-cresol, p-cresol, furfural and syringol are thought to have the largest impact on wine sensory qualities (Section 1.8).

Prevention and Treatment

Testing grape lots for 4-methylguaiacol and guaiacol prior to harvest will help identify lots that are at greatest risk of developing smoky characteristics during wine production.

Sulfur Taint

Sulfur taint is caused by elevated contents of volatile sulfur-containing compounds (VSCs). Sulfur compounds in wine usually present problems for several reasons: they have low thresholds for sensory detection and are generally associated with negative aromas. Negative odors associated with sulfur are rotten egg, fecal, rubber/plastic, burnt match, burnt rubber, and rotten vegetable. The principal offending compounds are hydrogen sulfide and higher sulfides such as mercaptans, disulfides, dimethyl disulfide, and other sulfur-amino acid metabolites.

Hydrogen Sulfide

When young wines start displaying a reductive flavor (e.g., rotten eggs) during, or shortly after fermentation, hydrogen sulfide (H2S) is usually the most predominant one of the VSCs involved. Hydrogen sulfide aroma is a serious fault in wine and will result in quality loss in the final product. Hydrogen sulfide an odor threshold of only 0.9 to 1.1 micrograms (?g) per liter for white wine and 1.6 ?g/L for red wine (Harrop, 2017).


If hydrogen sulfide is not removed from wine, it can react to form ethyl mercaptan which is known to have a burnt match, earthy smell. Once converted into ethyl mercaptan this compound becomes harder to remove from wine because of its higher boiling point. It also has a low sensory threshold of 0.02 to 2.0 ?g which makes it one of the smelliest substances that exist.


Disulfides are common in wine, but are usually found below sensory thresholds. They are typically formed after fermentation from oxidation of sulfide or mercaptan precursors. They are a serious concern due to their propensity to revert back to mercaptans.

Prevention and Treatment

There are several approaches to minimizing or removing excess hydrogen sulfide:

Volatile Acidity

Volatile acidity (VA) is a measure of the wine's volatile (or gaseous) acids. The primary volatile acid in wine is acetic acid, which is also the primary acid associated with the smell and taste of vinegar. Because it's a natural product of fermentation, VA will always be present in some concentration but tends to go up with time as a wine ages because of ongoing microbial activity. Generally perceived as the odor of vinegar, volatile acidity or acetic acid has a reported aroma threshold in wine to be as low as 0.1 to 0.125 g/L, depending on the style of wine and the individual.

Prevention and Treatment

Encourage healthy and fast-starting fermentations through proper yeast hydration strategies that include the use of a yeast hydration nutrient. Choose and use pure strains of yeast that are proven to be low producers of acetic acid. Eliminate or control the population of fruit flies by keeping all tanks covered. Avoid cross-contamination of different lots of wine, sanitize all sample devices, valves, and wine thieves.

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