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17th February 2015

A Taste of Taste!

Have you ever wondered exactly what your wine tastes of? Or for that matter, wondered why wine-geeky people talk of wines tasting of a plethora of things other than grapes, or any kind of fruit for that matter?

The answer is that wine, like everything in nature, tastes of the chemicals that make up its complex flavour profile. Fermenting fruit will break down the juice and reassemble the component parts, which is why the only wines that smell and taste of grapes are those where some of the grape juice has been left unfermented (principally some wines made from Muscat and Riesling). But wine made from grapes can also display the aromas and flavours of a whole bunch of other substances that originate from the fruit, from the ground in which it is grown, and from the yeast that ferments it.

A small knowledge of the chemistry involved can really help understand what is going on, and serves to illustrate that it may well not be “pretentious” to describe a wine as tasting of apple, blackcurrant, herbs and spices, but actually chemically true. And there are some entirely explicable flavours going on that can be even more bizarre than the most florid of wine journalists “descriptions” - flavours of mushroom and bacon for example.
Broadly the flavour compounds fall into these groups: Fruit, Floral, Herbal, Spicy and Earthy.

Esters are nature’s flavour building blocks. They are found across a range of fruits, and are common to many of them. If you have ever tasted raspberry or banana in a wine, then it is because of these esters. The grape variety Pinot Noir, for example, often carries flavours of strawberry (sometimes cooked or preserved), while Grenache can produce raspberry notes, and Chardonnay and Chenin Blanc often have an appley touch. All because of esters.

Pyrazines are common components of vegetable and bean flavours. From the under-ripe characters of grass and asparagus, through elderflower and green pepper/capsicum, right the way to bitter chocolate and coffee characters, pyrazines flavour flower, fruits and vegetables of all natures. In wine, the gooseberry character of Sauvignon Blanc and the leafy bell-pepper qualities of Cabernet Sauvignon (which are, as the name suggests, related) are all down to pyrazines.

Terpenes are intensely aromatic. They can be responsible for the floral aromas of rose, honeysuckle and lavender, but in extreme amounts can be resinous, and pungently bitter-herbal. A major component of the hops used in brewing, for example, terpenes in wines range from the aromatic lychee/litchi qualities of Gewürztraminer and the orange touch of some Muscat, through to the violet, eucalypt and sage notes of good Shiraz.

Thiols are part of a group of compounds called organosulfates (also types of esters). In small amounts they can add delicious characters of the mildly bitter-sweet like blackcurrant, grapefruit (especially pith) and passionfruit. However, too much and the aromas become sulphurous and can resemble garlic. You might not be a vampire and really enjoy garlic, but it’s not likely that you want it in your wine. The blackcurrant-leaf qualities of good Cabernet Sauvignon and the grapefruit-pith notes to be found in Vermentino are all a legacy of thiols from the fruit. A particular thiol, Rotundone, is responsible for the peppery flavours in Syrah and Grüner Veltliner.

Sulphur/Sulfur itself, which may come from the fruit, the soil, or the yeast, is responsible in large part for the aromas and flavours of minerality in wine. From the chalky freshness of a good Chablis to the flintiness of classic Sancerre and earthiness of Rioja, these mineral qualities are less to do with the grapes the wine is made from as the place those grapes were grown - a concept the French refer to as ‘terroir’ or a sense of place. Too much sulphur of course can smell bad and somewhat cabbage-y. This natural sulphur component is not to be confused with added Sulphur Dioxide, which is used by winemakers to control oxidation and disease, and if over-used can smell of struck match or even stale eggs. Sulphur Dioxide (SO2) in high concentrations can be a known allergen, and its use has to be recorded on the label.

Volatile Acidity is - in essence - vinegar, a conversion of the acids, and oxidation of alcohol, in the wine to acetic acid as a result of bacterial action. It is entirely natural and in very small concentrations can enhance the flavours in the wine with balsamic touches, adding complexity. Too much, of course, and the wine is ruined. Some Italian wines, especially those from hotter, sunnier climes, where the alcohol levels are also higher and protective can benefit from hints of volatile acidity.

Phenols are naturally occurring, pungent chemicals. They occur in pepper, sesame, hops and some grape skins. One phenol is the wild yeast, Brettanomyces, which often exists where grapes are grown. It can impart savoury flavours of bacon, cloves and leather. But in extreme doses the flavours become positively horsey and tend to dominate the fruity qualities the wine may have had. Some warm grown areas , like Châteauneuf-du-Pape in France are noted for Brettanomyces.

Geosmin is a bacterial organic compound and responsible for earthy flavours in wine. From the sweetly acrid qualities of fresh potting compost to beetroot, truffle and mushroom aromas, geosmin is another seasoning flavour that can really enhance a wine if the balance is right, but overpower if it exists in excess. Wines from Tuscany and parts of Spain can offer the best examples.

Lactones are esters that are the result of the action of lactic bacteria on chemicals (mainly acids) within the wine. They produce flavours of cream, butter, milk and yoghurt (even cooked pork has lactone flavours!). Often sweetish, and accompanying the vanilla flavours of ageing in oak, lactones can be an important flavour in barrel aged Chardonnay.

Botrytis is a type of fungus, or rot, which punctures the skins of grapes and consumes water, thereby concentrating the sugars and acidity. You will have seen Botrytis in a punnet of strawberries that has been left a tiny bit too long - it’s the furry part! In some wine grapes, however Botrytis is beneficial and its ability to concentrate sweetness makes it responsible for many of the great dessert wines of the world, such as Sauternes and great late harvest German Riesling. For this reason, it is also called ‘Noble Rot’. It leaves behind a distinctive flavour of honey, marmalade, ginger and rye-bread

Unlike a chef who can add ingredients to a recipe or with their imagination, the winemaker has only the power to try to capture the precise balance of the chemical constituents above as given to him or her by nature. Truly great wines are noted by their complexity of flavour, but with an emphasis on balance. It is almost as though the more complexity that the wine has, the more difficult it is for the consumer to pick out individual component aromas and flavours. Just as with fine cooking, the flavours should last - even when the wine has slipped down - without any one element dominating the others. Concentration of fruit in the vineyard and careful control of the winemaking processes are the only way for a great winemaker to be able to harness the best of nature, which is why the finest of wines often carry a price-tag to match. But just as with fine cuisine, sometimes it is worth spending the money!


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