Analysis of Wine Legs

March 25, 2009 (in Process)

Wine legs: what they can tell you about a wine when performing blind tastings

Background

This quick research paper was prepared after a blind tasting flight, one night at my winery. I was discussing with a co-worker, how to determine alcohol levels in wine by looking at the various types of legs produced. Then the CEO of my winery disagreed and said you could tell very little about a wine, and that legs were more a matter of viscosity and sugar levels which pretty much nullified being able to determine alcohol percentage just by looking.

Objective

To be able to determine one way or the other if wine legs or tears can actually tell us anything about the wine we are drinking, and whether it can be used at a tool in professional blind tasting.

Forward

I expected my little research topic into wine legs to be straightforward, fast and absolute. After all there is a huge volume of literature and research on the topic, and I naively assumed that after hundreds of years of authors writing about wine, that there would be general consensus on the topic. Never did I imagine that my research would take me into the areas of physics, surface tensions, surfactants, and more advanced scientific principles which I reluctantly had to wrap my head around to get my core question answered.

Illustration 1: Wine Tears, Chelsea Elizabeth Photography

What are wine legs?

Simply put, the legs that appear to cascade down your glass are alcohol evaporating. Like everything in life, the full explanation is not so simple. If you were to dissolve honey in water, and swirl the glass, this would also give a result similar to ‘wine legs’ by coating the glass with a thick, viscous film.

Types of Wine Legs

One of my wine instructors gave the following observation about the various types of legs, they are a visual representation of the body of the wine. He had the following observations based upon nearly fifty years of industry experience:

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Tears or Thin Rivets, indicates a light body
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Cathedral Windows – Medium Body
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Sheets – Heavy Body

(Try to find photos of the three types of legs)

These observations hold true as a general rule in wines produced in a cold weather viticulture region, how ever wine from warm weather viticulture regions will raise the alcohol percentage considerably (due to picking the grapes at phenolic ripeness and the correspondingly high sugar content). Also, sweet wines have a noticeable increase in glycerol, which tends to give leg formation at lower alcohol percentages.

Can legs give you an indication of the quality of a wine?

Legs are easy to identify, but they aren’t easy to interpret. In general, prominent, slow-dripping legs tend to indicate a wine that’s of some viscosity and thus more likely to taste fuller bodied. (Oldman)⁠

Can you determine the alcohol percentage of a wine by looking at the legs.

Speed that legs drip down the glass

Wines high in alcohol take longer to evaporate, thus the higher the alcohol content, the slower speed the legs run down the side of the glass. (Best)⁠ Leg speed does give an indication as to alcohol percentage.

Pigmentation in Legs

The physics behind wine legs

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Capillary Action
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Surface Tension
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Interfacial Tension
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Evaporation
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Refractive Index

Gibbs-Marangoni Effect

Two definitions.

The legs occur due to the Marangoni effect. It comes from the fact that alcohol has a lower surface tension than water. Wine is mostly a mix of water and alcohol plus a few other parts such as sugars, tannins etc. As you swirl your wine around the glass and leave some on the side it starts to evaporate. Alcohol evaporates faster than water due to its lower boiling point and higher vapour pressure. The changed alcohol to water mix now has different surface tension areas. The wine forms droplets in the areas of least / most resistance which fall back down the glass under their own weight. (Svans)⁠

Ethanol evaporates from the beverage where it is wetting the sides of the glass. In the absence of ethanol, the surface tension of the liquor on the sides increases, so it contracts to minimise the surface area. This in turn brings more ethanol-laden liquor to the top and starts to form ‘tears’. The tears form at the highest point, since there is less ethanol there. As the process continues, the tears become large enough that they roll down under their own weight. (Central Chemical Consulting)⁠

Ambient Temperature and it’s Effects on Wine Tears

The ambient temperature of the wine and tasting room directly effect the rate of alcohol evaporation. Thus a wine served cold will evaporate slower and it’s legs will be less pronounced than a wine served warm.(Best)⁠

Surfactants and their effect on wine legs

Surfactants, most noticeably dish detergent and soap, but also any oily residue on the wine glass will impede legs from forming, as the soap residue leaves a thin film between the glass and the wine.

Surfactants are of particular concern when tasting Champagne or Sparkling wine as any residue or dirt can seriously impede or degrade the mousse. (Jackson)⁠ Rinsing glasses in very hot water (170 – 180 degrees) can eliminate any films, also, washing glassware in salt-water is a time tested approach to avoiding any surfactant residue, while still sanitizing the glass.

Extract and effect on body

Short version is that low alcohol alcohol wines always have decreased legs, regardless of total amount of extract, thus do not impact body, nor conversely the viscosity of the wine.(Best)⁠

Judging Viscosity in the Glass

Viscosity refers to a wines consistency, and how it tumbles in the glass. Viscosity can range from thin to syrupy.

Glycerin content and viscosity

Glycerol is commonly believed to be the determining factor in the body of table wine. With the exception of late harvest or dessert wines, this is not true. The main component of body is proven to be ethanol.(Wine Virgin)

Viscosity is effected by the levels of glycerols (sugars) and alcohol found in the wine. Generally speaking, the higher a wine’s levels of glycerols and alcohol, the higher the wines viscosity will be. (OregonWines.com staff)

Most table wines have a glycerol ⁠levels of 5 – 10 g/l, however viscosity is not effected until levels exceed 25 g/l. Thus the glycerol content of a table wine has no effect on body. (citation)

More about Glycerol from the Waterhouse Lab, UC Davis

After ethanol and carbon dioxide, glycerol is the most abundant product of yeast fermentation (Ribéreau-Gayon et al., 1998). Several parameters have been shown to influence the final glycerol levels in wine. These include the ripeness of grapes, the microbial flora on grape berries and cellar equipment, as well as the pH, fermentation temperature, the nitrogen source and the yeast strain (Scanes et al., 1998). Glycerol is typically found at concentrations of 4 -10 g/L in dry wine and in the case of the botrysized late harvest wines, levels in excess of 20 g/L are not uncommon (Ribéreau-Gayon et al., 1998). In the latter case, grape berries infected by Botrytis cinerea already contain significant amounts of glycerol as a result of the metabolism of the fungus, which explains the high glycerol levels commonly found in this wine style.

It is frequently suggested by winemakers, enologists and wine writers, that glycerol contributes positively to wine quality. The perceived contribution has been defined in terms of mouth-feel and texture properties, and is thought to be strongly dependent on the glycerol concentration in the wine. In general, higher glycerol levels are considered to improve wine quality. To date, the opinions regarding the relationship between glycerol and wine quality appear to be based on anecdotal and empirical evidence. In some instances, clear anomalies exist between the perceptions and actual data that have been obtained through experimental work. No positive relationship between glycerol per se and the mouth-feel attributes of wine has yet been established and several factors other than glycerol have been implicated in mouth-feel. These include the ethanol concentration, the yeast cell wall mannoproteins, barrel maturation, yeast autolysis, the yeast strain used, as well as phenolic compounds in red wines (Ribéreau-Gayon et al., 1998; Deltail & Jarry, 1992). Furthermore, at the concentrations at which glycerol is normally found in wine, the impact that it could have on the viscosity of wine would probably not be perceived by even the most experienced tasters (Noble & Bursick, 1984). Against this background it is quite possible that the perceived contribution of glycerol to mouth-feel can easily be over-emphasized. (Waterhouse)⁠

Related Content: Cold Fermentation and it’s Effects on Viscosity

While researching this paper I came across a note by Jancis Robinson: “Low-temperature fermentation tends to increase viscosity slightly, however”.(Robinson)

Some digging in research papers turned up scores of information about fermentation temperatures and how it effects wine in all areas, not just viscosity. There is much to analyze, and I will probably develop another research paper to do justice to this topic.

The short answer is that trials and research tends to support Robinson’s claim, but due to the complexity of the subject I am not including it in this paper at the present time. ⁠

Dessert and Late Harvest Wines

Sweet wines typically contain 20 – 25 g/l of glycerol, which will effect the viscosity, thus the legs. (Best)⁠ Botrytis-effected wines naturally have high glycerol content due the the metabolism of the fungus and it’s effect on the grapes. (Waterhouse)⁠

Conclusions

With a lot of ground covered I hate to say that I have no definitive conclusions if a wines legs can determine alcohol percentage of wine.

The speed of which the legs fall back into the glass do indicate the percentage of alcohol present, but this is an empirical observation.

Likewise the different leg patterns do tend to indicate body or viscosity, however when dessert wines are added to mix, the waters get muddied.

Swirling the wine should give an indication of viscosity (at least to an experienced taster) and may make it possible to state that a thick viscous wine is a dessert wine, and to judge the legs accordingly.

Wine temperature and it’s corresponding evaporation rate adds a nice twist to evaluating legs, which can be overcome by being consistent on serving temperature for blind tastings.

I am still looking for more research in this area, and may do some experiments in the near future to try to prove what I think to know to be true, but cannot prove. As there is so much anecdotal and empirical information on the subject, maybe a controlled series of experiments is just what is needed to prove or disprove what exactly can be determined from looking at wine legs.

Works Cited

Best, Richard. “The Frugal Oenophile’s Wine Newsletter – June 2005.” Jun 2005. 20 Feb 2009 .

Central Chemical Consulting. “Tears in alcohol.” 2 Mar 2009 .

Jackson, Ron S. Wine Science: Principles, Practice, Perception. 2nd ed. Academic Press, 2000.

Oldman, Mark. Oldman’s Guide to Outsmarting Wine. First. Penguin Books, 2004.

OregonWines.com staff. “08. What is meant by a wine’s “viscosity”? What factors can affect it? – Oregon Wines.” Oregon Wines.com. 20 Feb 2009 .

Robinson, Jancis. How to Taste: A Guide to Enjoying Wine. First. Simon & Schuster, 2001. 3 Mar 2009 .

Svans, Peter. “What Are Wine Legs and What Causes Them?.” 20 Feb 2009 .

Waterhouse, Andrew, L. “Red Wine Composition, Minor Components.” Waterhouse Lab, UC Davis. 3 Mar 2009 .

Wine Virgin. “Do Your Wine Legs Have Body? | The Wine Virgin.” The Wine Virgin. 20 Feb 2009 .