I am not sure how many of you liked science at school, but I actually found it quite fascinating (except the exam part of course). Once one starts to appreciate the wonder of nature and how we as humans perceive it, we realize what a wonderful role chemistry plays in our everyday lives! The same applies to wine and we as wine researches are trying to match the chemistry of wine with the taste of it. Now, we often talk about tasting wine, which is actually not a bad hobby as most of you would agree. However, we can only perceive five different tastes, which are bitter, sweet, salt, acid and umami (the latter is the taste one finds in soya sauce).
However, we can smell a wide range of different aromas, which is also the case in wine. This is due to the many different flavour compounds occurring in wine and the wide ranges in which these compounds occur. The aroma compounds in wine (more than 800 have already been discovered) basically comes from 4 sources. These are the grapes, the yeast, wood derived aromatic compounds and those forming over time while the wines mature in the bottle. This post is not really about these difference origins, but rather to show you how wide these ranges of different compounds can be in wine and how we perceive them. The range that we can perceive aromas in wine also differs a lot, with humans being able to smell certain compounds at a million times lower concentrations than others! Some compounds we can perceive in wine at milligrams per litre or mg/L, others at a thousand times less at microgram per litre (µg/l) and others at a million times less at nanograms per litre (ng/L). I would like to illustrate this with the following picture (the chemical structures of the compounds are also shown for those of you who like chicken wires).
On the left one can see for instance sulphur dioxide (sulphur like aroma) and an ester (iso amyl acetate, banana like). Both of these occurs in wine normally at mg/L, levels at which we can smell them. This equites to you dissolving 6 grains of salt in a litre of water and being able to perceive it. Certain other aroma we can perceive at µg/l, or the equivalent of these 6 grains of salt being dissolved in a 1000L of water or a small swimming pool. This is true for compounds such as terpenes which has a rose, fruity aroma or volatile phenols with a medicinal aroma for instance. Others we can smell at much lower levels, that is at ng/L, which is the same as us perceiving the 6 grains of salt in half an Olympic size swimming pool or a million litres of water! The latter is true for instance for certain methoxypyrazines or volatile thiols, which causes the green pepper aromas and passion fruit aromas in Sauvignon blanc, respectively. All of this makes research in wine very challenging, but also fascinating!