Wine aromas and their precursors in grapes

Discussing the aromas in a wine can sometimes be like flogging a dead horse, and is often a controversial subject. So we are throwing open the doors and letting in a breath of fresh air with scents to awaken our senses.

Let me be clear – I will not be listing the seven aromatic components appearing in wine, but instead I will be attempting to shed some light on where they come from.

In another article, Harald discussed the three categories of aromas, coming from the grape’s metabolism, that of micro-organisms, and a wine’s maturation and development. Thus far, things are simple and universally agreed upon. Now things get more complicated, as we are looking at aroma precursors and the source of development for maturation aromas.

Precursors can be split into two major categories based on the position of the aroma molecules:

• If attached to a sugar, precursors are broken down into fruit aromas, and can be found at approximately the same intensity level in young wines.
• If attached to an amino acid, the molecule is completely odourless in the grape and is only revealed during the fermentation process. Thiols, which are so sought-after in our Sauvignon Blancs, thus develop rhubarb, boxwood, grapefruit, sweat, mango, broom and exotic fruit aromas.

However, before working to ensure that the aroma precursors are transferred into the must, using enzyme activity in the yeast to transform them and striving to preserve them in the wine, it is vital to boost their concentration levels in the grape itself. In order to do so, we must step slightly away from the sacrosanct ‘winemaker’ and instead look at the expertise of the people that work the land. They can only partially compensate for extremes of climate, but their agronomic activities of planting the right rootstock, managing planting density, plot cultivation methods, plant balance, harvest dates and more enable them to control the complexity of the winegrowing factors that have an impact on wines’ aromatic potential. Control…

The plant’s water and nitrogen supply during the weeks leading up to the harvest will assist vineyard workers in their efforts. Slight water stress and no searing heat after veraison is good for Sauvignon Blanc (that grape again), but if it persists, the lack of balance in the grapes will be irreversible. The option to irrigate part of the plot goes some way towards correcting certain vagaries of weather. It is all a question of balance…

For leaf thinning, an attentive winemaker will reduce the shade covering grapes, which has a major impact on their aromatic potential. However, seeking better light access via long, direct exposure to the sun can ruin their efforts. Then it becomes a question of balance…

Not all grapes react to sun exposure in the same way. Balance comes from the perfect pairing between the nature and colour of the soil, and its ability to absorb and pass on rays. It is all a question of adapting…

The skin is the primary home of these direct aroma compounds or precursors of future aromas. Its surface hosts the various different elements of its eclectic flora, promoted or eradicated in turn by the climate and cultivation methods used. Moisture, for example, which we know is beneficial for the plant, also aids the development of mould, which then comes through as earthy or mouldy flavours once in the vat. Not all of the aromas found in the grape will improve the wine’s organoleptic qualities, and thus not all should be expressed. The green pepper aroma that is strongly present in the skins of some red varieties is one of these. The molecule responsible for this aroma is synthesised during the plant’s growth cycle, from fruit set to veraison (essentially June to August). It is sensitive to light and temperature, and will be broken down and diluted as the grapes increase in volume during ripening. The point when the green pepper aroma begins to degrade is also the point at when the sought-after blackberry and blackcurrant aromas gain traction. A change of weather at this pivotal point, light that shines early, late or too strongly on the fruit-bearing area, can efficiently prevent mould from developing but also irreparably compromise the wine’s future aromatic expression. Swings and roundabouts. It is all a question of balance…

All of the components made in the grapes or created and biosynthesised during the process of turning must into wine are vital for aromatic development. However, each of the different stages of fermentation can reveal or destroy aromas. There is therefore an ongoing balancing act governing the development of aromas or their precursors, and a trained person will not be flogging any dead horses. Attentive and restrained, rigorous and selective, quite simply they sometimes hold the keys to their particular approach to the winemaking process. And with climate change, they have multiple keys on their keyring.