Cici Muldoon provides the 45th published entry into our wine writing competition. Don't forget that we will be asking you to vote for your favourites on Friday 7 April.
My name is Cici Muldoon, I am 33 years old, and I am an avid oenophile, physicist, and wannabe ballerina. I am the founder and CEO of VeriVin, an innovative startup developing a unique non-invasive wine analyser and working on the quantum-enhanced spectroscopic sensing of trace compounds in sealed containers. I studied physics and finance at Princeton University, and hold a PhD in experimental Atomic and Laser Physics from Oxford University, where my PhD work focused on cold atom trapping and manipulation as a step towards the eventual implementation of a quantum computer. My passion for wine began at Oxford, where I was president of the Oxford University Wine Circle and co-captain of the Oxford University Blind Tasting Team, and I am a current WSET Diploma student (hopefully done in June!). I speak five languages, and my other two lifelong passions are ballet, which I still practise almost every day (performing in June!), and classic cars, which I am learning to judge and restore. I am originally from Mexico and I live in Oxford, England.
DOES WINE REALLY SMELL LIKE BLUEBERRIES?
Is there a scientific basis for the flamboyant aroma descriptions which can often be found on labels or in menus? Isn’t it down to individual perception?
Yes, and yes. To a certain extent, a wine’s bouquet will be different for every person that smells it, because the smelling apparatus of each individual will be slightly different, and because the smells the individual has been exposed to throughout his or her life may be different, or have different names. Even the environment in which the individual is smelling a wine may have an effect on its perceived aroma. However, chemically speaking, there are indeed molecular compounds which are associated with the smell of certain well-known foodstuffs or other substances – whether because they are naturally present in that substance or foodstuff, or because they have been used to mimic the aroma artificially – and some of these molecular compounds can be found in wine. Their presence and concentration will depend on a number of factors, including the grape variety and various choices made by the winemaker (eg oak maturation, anaerobic winemaking, cold fermentation, etc).
Some smells are almost unmistakable and are predominantly attributable to a single molecular compound which is naturally present in the foodstuff with which the smell is associated. For instance, the smell of vanilla derives predominantly from a phenolic aldehyde called vanillin, which occurs naturally in cured vanilla pods. Some smells are more complex, and attributable to several different molecular compounds which are all naturally present in the foodstuff with which the smell is associated. For instance, there are more than six different aroma compounds that can be associated with the smell of pineapple, all of which are naturally present in pineapples. Some 'unmistakable' smells are attributable to a molecular compound which is regularly used as an artificial flavouring, to mimic the smell of a particular foodstuff. For instance, the smell of banana is regularly mimicked using a simple ester called isoamyl acetate, which is naturally present in bananas but only partially responsible for their smell. So strong is the association of isoamyl acetate with the smell of bananas that it has come to be called the banana ester by chemists.
It should of course be emphasised that just because a wine is redolent of strawberries does NOT mean that strawberries were blended into the wine.
In sum, there is indeed a scientific basis for the description of a wine’s bouquet in terms of the smell of existing foods or substances, and to the trained taster, a description using this vocabulary can indicate something about the grape variety/ies, the winemaking techniques, and even the geographical origin of the wine. This description is not necessarily 'correct' and may differ wildly from an individual’s perception of the same wine, but it is valid and can be very useful. As with any language, it is a case of being able to interpret the terms used and mapping what one smells in the glass with the language that is usually employed to describe it. This aromatic language will undoubtedly have a strong cultural dependence. Perhaps more interesting in terms of interpreting what is in the glass is determining whether the perceived aroma is a simple or complex one… and whether it is pleasant!
THE ROLE OF SO2 IN WINE
In order to understand the role of added sulphur dioxide (SO2) in the formation of volatile sulphur compounds, it is important to understand why it is added to wine in the first place. SO2 is added to wine for its antiseptic, antioxidant and antioxidasic properties. It can be sprayed on grapes, added to must, used to arrest primary (alcoholic) fermentation, used to arrest malolactic fermentation, and added at bottling. SO2 exists in wine in more than one form. In winemaking, reference is often made to total SO2 being a combination of free SO2 and bound SO2. Bound SO2 is the fraction that has formed other sulphur-containing molecular compounds and can thus no longer play an antiseptic/antioxidant role. Free SO2 is the useful fraction, but even this does not exist purely as molecular SO2. In solution, SO2 exists as a combination of hydrogen sulphite (HSO3-), sulphite (SO32-), and S, like this:
SO2 + H2 —> (HSO 3)- + H+ —> 2H+ + SO32-
lower pH higher pH
(higher acidity) (lower acidity)
The balance between these three forms depends on pH. At wine’s average pH, the dominant form is HSO3-, although SO2 and SO32- will also be present. As the pH goes lower, the proportion of SO2 goes up, and that of HSO3- goes down; as the pH goes higher, the proportion of HSO3- once again goes down, and the proportion of SO32- goes up. Hence, it is a generally known dictum in winemaking that the more acidic the wine, the more SO2 is available to do its job, and the less of it that needs to be added.
It should be noted that SO2 in wine is not only useful but generally also harmless. The amount of total SO2 permitted in wine is regulated by law, and as such, will only be present in quantities which are safe for human consumption (of course this will depend on the laws of the region or country of production and adherence to those laws). In the EU, for instance, the basic legal limit for dry wines is 200 mg per litre for white wine and 150 mg per litre for red wine (red wine needs less sulphur dioxide because it contains more polyphenolic compounds, which act as natural antioxidants). That said, SO2 can cause an allergic reaction in some people, especially if they are prone to asthma or other allergies, and it is for this reason that most bottles now carry the phrase 'contains sulphites'. Also interesting to note is the fact that even organic winemaking permits the use of sulphur dioxide, and it is rare to see a wine made entirely without SO2.
The use of SO2 goes hand in hand with modern-day anaerobic winemaking, in which great care is taken to avoid oxidation at all stages of the winemaking process. Wines made in this way tend to be incredibly clean, fresh, and fruit-driven, in line with current preferences of the general public. The irony is that wines made in this way are also at a much higher risk of developing sulphur taint. Some experts think the levels of added SO2 should come down to as little as 5 mg per litre, especially for wines bottled under screwcap.
