Somm vs. Scientist: How Winespeak Relates to Chemspeak

The subject of wine bridges many different fields of study. Before developing a love for wine, I first acquired a love for science (albeit mostly due to the fact that appreciating science doesn’t have a legal age requirement), and when exposed to different disciplines or professions, one notices overlaps in terminology that, without clarification, can cause meanings to be lost in translation. The sommelier profession is no exception. As a former chemical researcher, I’m sometimes confused by discrepancies in the ways various terms are used in the sommelier community when compared to the scientific community. Some scientists might go so far as to call such rhetoric misnomer, but to me, it seems more like poetic license. I’m of the opinion that every profession should be allowed to develop its own vernacular based on its own distinct historical and etymological evolution. Should one criticize the singer who sings an unaccompanied vocalise marked a capella for not actually singing in the manner of the chapel? However, a certain amount of consistency between culinary and scientific usage is desirable, so that barriers to communication between sommeliers and people in the scientific wine-related community are not created. In the following text, I want to briefly elaborate on a few differences between winespeak and chemspeak, in particular, the concepts of oxidation/reduction and viscosity.

Oxidation and Reduction

The word "redox" comes from an abbreviation of “reduction-oxidation.” In present times, redox reactions relate to changes in states of hypothetical charge, and are explained through electron transfer. Electrons can be defined as small subatomic particles with negative charge; all atoms have electronsin their natural state. Reduction confusingly refers to chemical species (molecules, atoms, ions, etc.) “gaining” electrons. Oxidation is the opposite: it means species are “giving” or “losing” electrons. Here’s how I was taught to remember it:

OIL RIG
(oxidation is loss; reduction is gain)

One should note that the redox reaction is a concept designed to help explain phenomenon at a molecular level. It’s not literal description, and its conception predates certain scientific developments such as electronegativity theories. In other words, electrons, aren’t actually given and taken the way you can with apples or pennies.In the general sense of the words, oxidation and reduction are not separate reactions because where there is oxidation there is usually reduction. For one species to give another needs to take; oxidation and reduction happen at the same time. Hence the combination of the two terms into “redox”. When scientists refer to one without the other, they are usually focusing on one species, molecule or element that is important to the context, such as the oxidation of carbon or sulfur. In winespeak, the concepts are used in this way, oxidation referring to separate and different reactions than reduction. I find that’s not the part that confuses most people, however. What causes confusion is the fact that oxidation, despite its name, doesn’t necessarily have to have anything to do with oxygen anymore. But it did at one point.

Oxygen in the air (diatomic oxygen gas, O2) was discovered in the late 18th century (credited to either British clergymen Joseph Priestley or Swedish pharmacist Carl Wilhelm Scheele, depending on whom you ask), at which point French chemist Antoine Laurent de Lavoisier became very interested in its qualities. Lavoisier coined the word "oxygen" after the Greek terms for "becoming sharp" because for some reason he thought that the sharp taste of acids came from oxygen. He was wrong, but the word stuck. Lavoisier, however, correctly related oxygen to combustion reactions and the rusting of metal, or in other words, the creation of metal oxides. Oxides are chemical compounds that contain oxygen and one other element such as iron (e.g. ferric oxide, Fe2O3, associated with rust) and can be formed through reactions between the element and oxygen. Oxides can also undergo reactions to lose oxygen. Lavoisier and other early scientists noticed that certain metallic oxides could be heated to extract the metal itself and that they lost mass in this process. The oxide was being "reduced" to metal, and this is where the original concept of “reduction” came from. By today’s scientific definitions, oxygen is not the only oxidizing agent, oxidation does not have to include addition of oxygen, and reduction does not have to create a loss in mass. In a sense, the terms “oxidation”, “reduction”, and even “oxygen”, are themselves misnomers. Scientists later realized more accurate ways to describe these concepts and reactions, but the terms caught on, became entrenched, and nobody really wanted to change them. Etymological results of the process of history.

So where did the descriptor “oxidative” enter the etymological process for sommeliers? From a specific field of chemistry - organic chemistry. Organic compounds are those that contain carbon, and wine, like anything else composed from once-living matter, is full of them. Organic chemistry often refers to organic compounds as being “oxidized” when the carbon in the compound loses electrons to oxygen, such as in the oxidation of alcohols to aldehydes, carboxylic acids and ketones. These reactions result in an increasing number of bonds between carbon and oxygen, and the carbon loses electrons to oxygen by the creation of these additional bonds. Hence, it is oxidized.

These oxidation reactions can have different relationships to oxygen than the reactions that involve metal oxides. For example, when ethanol (CH3-CH2-OH), which is the chemical alcohol in vernacular alcohol, undergoes oxidation it becomes ethanal (CH3-CHO), more commonly known as acetaldehyde. In this reaction, more oxygen is not added to the molecule, but instead two hydrogen are lost and the number of bonds between carbon and oxygen increased. The reaction is considered an oxidation even though reactions with additional oxygen may not be directly involved. With wine, the conversion of ethanol to acetaldehyde often results due to the presence of oxygen in the form of O2, but not necessarily due to the O2 reacting directly with the ethanol. Under many conditions, O2 can oxidize phenolic compounds in the wine to form more reactive substances like hydrogen peroxide, which can then undergo oxidation reactions with either ethanol or other phenolic or non-phenolic compounds. The products of these reactions can undergo further oxidation reactions to create different compounds such as acids and esters, like acetic acid or ethyl acetate, and the reactions can continue, on and
on. Wine, like language, has the capacity to evolve perpetually.

So what does the term "oxidation" mean in an aromatic sense? Technically, by scientific terms, oxidation by O2 is almost always happening to some component of the wine at some level as long asthe wine isin contact with some amount of O2. The sense of perceptible “oxidation” that sommeliers are concerned with relates to a wide range and diversity of aromas that arise due to levels of acetaldehyde and/or other products of oxidation reactions reaching different sensory thresholds. Usually the presence of a high degree of these compounds is considered a fault, but a certain degree may be considered desirable and even indicative of classic styles. Most of the time, the presence of O2 is the key component in initiating these oxidation reactions, and therefore, sommeliers are not being inaccurate when they link certain aromas to the presence of O2. However, sommeliers should remember that many “oxidative” aromas do not develop just because the wine was aged or just because it was exposed to too much air. What matters are the stage, type, and/or degree of certain redox reactions caused by exposure to O2. These aspects depend on winemaking factors such as the amount of O2, the duration and timing of exposure, whether there is exposure or absence at a specific points in the process, and very importantly, what chemical compounds, as well as catalysts and micro-organisms, are present at the time (which relates to viticultural factors as well). It should also be kept in mind that wine that does not smell “oxidative” has also likely been exposed to O2 at some point, and such
exposure is usually desired at certain points in making any wine.

This brings us to the term "reduction." What gets a little confusing is when no distinction is made between reference to “reduction” in the sense of there being an absence of oxygen, and “reduction” in the sense of “reduced” sulfur, where sulfur is in a state where it is gaining more electrons when compared to another state. The two are related: in winemaking, reduced forms of sulfur can result in “reductive conditions” where exposure to O2 is limited in some way (but keep in mind, reductive conditions do not necessarily have to relate to O2 as the controlling factor). Therefore, for sommeliers, the indicator of this kind of vinification is often a smell that is associated with sulfur compounds. Sulfates contain sulfur bonded to four oxygen atoms (SO42-), and are considered oxidized forms of sulfur. In other words, the sulfur is losing electrons to the oxygen. Sulfites only have three oxygen atoms (SO32-), and can be considered “reduced” compared to sulfates, which have more oxygen taking electrons from the sulfur, or oxidized in comparison to compounds that contain sulfur that is not bonded to oxygen. Sulfur dioxide (SO2) in its molecular form is technically a sulfur oxide and not a sulfite, but it is often lumped together with sulfites because it converts to sulfites in the presence of aqueous base, or water. A certain amount of molecular SO2 can smell like matchstick, and some wine people associate SO2 with “reductive” wine conditions because usually it is added to the system intentionally as a method of reducing oxidative aromas. Technically, SO2 does not prevent oxidation so much as the smell of it, or the stage of it. It doesn’t really prevent O2 from reacting with components in the wine, and while it can react with hydrogen peroxide to partially prevent further oxidation reactions, its more important role is to bind to the smelly products of wine oxidation like acetaldehyde.

What is most often meant in winespeak by “reduced” sulfur forms are volatile compounds where sulfur is not bonded to oxygen, such as sulfides and thiols (mercaptans). The most notable sulfide in wine is hydrogen sulfide (H2S), which can produce rotten egg smell and can be detected at very low quantities. H2S can be created at different points in the winemaking process, such as during fermentation or postfermentation aging on the lees. Factors such as levels of elemental sulfur, SO2, organic sulfur-containing compounds, nitrogen limitation, and vitamin deficiency can all effect sulfide production. Sulfides other than H2S and disulfides in which two sulfur atoms are bonded together can produce off-putting odors like rotting cabbage or burnt rubber. In general, higher amounts of these sulfides are needed to reach sensory thresholds than for H2S and thiols, but they can be difficult to remove and some disulfides can revert to even worse smelling thiols in bottle. H2S may be treated with techniques like copper, but left untreated, H2S may also form thiols.

Another name for thiols is mercaptans. “Mercaptan” was a word coined by a Dutch scientist in 1834, because to him the compounds "captured" mercury (really, it just reacted vigorously). This term is still in use scientifically, but many use the term “thiols” as it is more in line with the universal standards of IUPAC nomenclature (see note below). Thiols are basically compounds with carbon bonded to sulfur and hydrogen, a sufhydryl group (-C-SH), and can occur in wines due to a myriad of factors in the winemaking process. Like sulfides, many of these compounds are described as having aromas such as rubber, burnt rubber, rotting cabbage, garlic, and onion.It should be noted that there are other types of sulfur molecules, like thioethers, which may give reductive smells and are not classified as thiols. Also not all thiols, sulfides and sulfur compounds give off scent or give unpleasant or unwanted scent. Some can contribute to a coffee-like smell, and others can smell like grapefruit. As well, there are many aromas that can result from “reductive” winemaking conditions that do not involve sulfur, and just like with oxidation, the presence of reductive aromas are not necessarily a fault. It is the nature and degree of the aroma created by “reductive” processes that will determine this.

The terms “oxidative” and “reductive” have already become commonplace descriptors for wine aromas. They are more complicated terms than other wine descriptors - the ideas that are conjured from the use of “oxidative” as a wine descriptor are not as simple as those evoked by descriptors like “bruised apple” - but the beauty of wine can lie within its complexity. As scientific knowledge about wine increases and this knowledge is imparted on more sommeliers, the aromas, tastes and textures that result from redox reactions may become more defined, along with the terms used to describe them. I expect, and desire, that both sommelier and scientific fields will evolve together.

Viscosity

Many sommeliers find it useful to swirl or coat the sides of the glass with wine and observe the “tears” or “legs.” Some refer to this as analyzing the “viscosity” of a wine, the purpose being to get information about alcohol and sugar levels, and perhaps also some information about extraction. In everyday usage, people relate the word “viscosity” with how thick a fluid is. The term originates from the Latin word for mistletoe, viscum, because mistletoe berries were used to make a viscous, gluey birdlime to trap birds. In science, however, the concept of viscosity, which can be defined as a resistance to flow, relates to fluid motion and fluid dynamics, which are very complicated fields that factor in molecular
considerations, thermodynamics, kinematics, and inertial forces. All wine possesses scientific viscosity, and it is true that viscosity can be related to alcohol and sugar levels in the wine, but many many other factors can affect viscosity. Observing minute differences in the definition of the legs of a wine may not always be an accurate method of assessing these relationships which are not always linear, particularly because the composition of different wines are so complex.

However, because some information is usually evident from examining the legs and the sommelier is not necessarily concerned with assessing fractional differences on a purely visual level, I see no harm in using the word “viscosity” to explain to customers and other professionals why the sommelier is drawing certain inferences from the legs. The practice itself is not unscientific to me. A sommelier makes assessments by drawing from experience, from trial and error in a multitude of different circumstances, and such expertise and use of human faculties has the potential to result in accuracy greater than deduction from an accumulation of isolated information from different experiments from different laboratories.
One thing that should be noted is that tears or legs in a wine do not form because of their scientific viscosity. If you put molasses in a wine glass, it will not form legs. Why? Because wine forms legs due to the different surface tensions and vapour pressures between alcohol and water. This effect has been called the Marangoni or Gibbs-Marangoni effect. Fluids will move from a lower surface tension to a higher surface tension, otherwise known as a tension gradient. Ethanol has lower surface tension than water. When you swirl and coat the sides of the glass with wine, the ethanol (which has greater vapour pressure than water) evaporates from this coating more quickly than from the wine in the glass, causing the surface tension of the liquid on the sides of the glass to increase due to there being less ethanol. This creates a tension gradient between the coating on the sides and the pool of wine in the glass. Wine is drawn up into the coating from the pool and the alcohol continues to evaporate. The water in the wine starts to draw together into droplets at the top, due to cohesion, and the droplets fall down the sides of the glass under the influence of gravity.

Accordingly, there are many factors that can affect the appearance of the legs such as temperature, the liquid-air interface, the condition and shape of the glass, and variables regarding the swirling or coating. Again, I bring this up simply to highlight the difference in mindset between a scientist and a sommelier, and not to denigrate the practice as obtaining no useful information, especially since the sommelier does not use this as their only input about the wine. Also, in my mind, the act of swirling the wine and observing the legs can provide a traditional aesthetic purpose, and aesthetics and tradition are more functional for sommeliers than scientists. I once had a wine expert ask me what I thought of the wine, “viscously-speaking”. The scientist (and grammaticist) in me wanted to reply that one cannot speak with viscosity. But the wine-lover in me instead just said, “It has nice legs.”

Some additional facts:

• If you think “redox” is a strange word, how about “phlogiston”? Phlogiston, a term with origins in alchemy in the late 1600s, was thought to be an element that was released from objects during combustion, and was the precursor theory explaining certain oxidation reactions before Lavoisier’s influence.
• Even though redox is usually explained through electron transfer today, it was once also explained as the loss or gain of oxygen, and also conversely, the gain and loss of hydrogen (electron “transfer” happens in all of these types of reactions, and is therefore the most all-encompassing method of explanation).
• “Redox potential" can be defined in different ways, but in aqueous solutions (solutions where the solvent is water, like wine) it's a measure of the tendency of the solution to gain or lose electrons when a new chemical species is introduced, and here's the neat thing: it's measured in volts, like with electricity and batteries because electrons are species with charge. Increasing oxygen exposure through techniques like racking can often raise a low redox potential number.
• Thiol is the preferred suffix for organic compounds with a carbon-bonded sulfhydryl groups used in the IUPAC nomenclature method (universal rules for naming chemicals) and it's used just like "ol" is used for alcohols. In chemistry, an alcohol is a compound with an oxygen bonded to hydrogen, (a hydroxy group, -OH). Ethanol is CH3-CH2-OH. Ethanethiol is CH3-CH2-SH. It can produce smells like burnt match.
• The Marangoni or Gibbs-Marangoni Effect is named after Carlo Marangoni who first studied it in the 1870s. James Thomson explained the phenomenon in his 1855 paper, "On certain curious Motions observable at the Surfaces of Wine and other Alcoholic Liquors". (Sounds like a fun thesis!)

Lisa N.S. Wong (B.Sc. (Hons), J.D.), majored in chemistry at Queen's University and has been employed as a researcher at such institutions as the Atomic Energy of Canada Ltd., Chalk River Laboratories, and National Research Council Canada, Steacie Institute for Molecular Sciences. She afterward obtained her J.D. from Osgoode Hall Law School (call to the bar, 2009), and has practiced intellectual property law and commercial litigation at a leading Bay Street firm. She is currently completing the sommelier intensive at the International Culinary Centre, California campus.