It’s in the soil: unearthing the truth about rocks and wine flavour

‘The rain quit and the wind got high, a black old dust storm filled the sky’ sang  Woody Guthrie, about the awful 1930s Dust Bowl in the American prairies. In my book it’s how I open chapter 15, ‘Four elephants in the tasting room’, in this case referring to the unacknowledged importance of the organic matter in soil, properly called the humus.  

The weathering that unlocks the crop nutrients in the soil’s geological minerals takes place far too slowly to produce a fresh suite each year, so it’s vital that the soil’s organic content is maintained. Its natural recycling not only provides the essential nutrients year on year, but they are much more readily available from humus than any geological mineral. 

So, the answer does indeed lie in the soil 

Some wine commentators like to claim that the nutrient minerals taken up by the vine roots reach the wine for us to taste, and enthuse about different kinds of source geological minerals and rocks. But in practice any soil nutrients that do get through to a wine will have largely come not from the geology but from the humus. And when did you last see humus mentioned in a vineyard description or in a wine-tasting note?  

Geology is so much more charismatic. Wine lovers don’t really want to read about rotted insects, decayed vegetation and the like so, well, the role of humus is simply disregarded. In other words, it seems to me, we have here an ‘elephant in the room’ (defined in my dictionary as a huge topic that is uncomfortable for people to talk about and so is ignored). 

Here's another ‘elephant’. When did you last see names such as Franz Richter, Georges Couderc, Federico Paulsen and Antonino Ruggeri in wine writings? They may be unfamiliar, yet it is scarcely an exaggeration to say that if it was not for the work of these individuals then wine as we know it might not even exist today. For they were the pioneers of grafting vines onto phylloxera-resistant rootstocks. And still today, most vine rootstocks have names like 110Richter, 3309 Couderc, and 1103 Paulsen. 

The uncomfortable truth about rootstocks 

Although during the phylloxera crisis the grafting solution was promoted as not affecting wine flavour, over time evidence otherwise has accumulated. For example, in one experiment wines from shiraz vines grafted on to 110Richter rootstocks relative to those grown on their own roots, had a more intense colour, darker berry aromas together with more intense and coarser tannins. In another test, 140Ruggeri rootstocks gave wines with relatively more acidity and higher anthocyanin/tannin ratios but were lower in polyphenols. For sure, the rootstock names hardly trip off the tongue but in view of all this shouldn’t they be getting some mention in wine reports? 

It’s similar, it strikes me, with yeast. A supplier’s catalogue notes that ‘choosing the right yeast for your wine impacts the taste, aroma, and overall quality of the wine’. One yeast strain, for example, is said to produce wines that have a ‘distinctive intense berry, graham cracker nose and a jammy, rich, very smooth complex profile’, another gives ‘bready aromas with vanilla notes’. 

…and what about yeasts? 

So the logic seems plain. Winemakers are choosing yeasts to help them achieve the kind of wine they’re striving for, so coming at it the other way round, a wine we are tasting must reflect the yeast that was used. And after all, it’s the yeast, ie. the fermentation, that produces the majority of the compounds that give wine its flavour. It’s why wine doesn’t taste like grape juice. So why isn’t yeast mentioned in wine reports? 

Most wine enthusiasts will know about extraneous factors that can affect taste perceptions. Best known probably is what we already know about a wine, its pedigree, cost, critics’ ratings, etc. They’re all in our minds as we taste. So the ‘elephant’ here isn’t about a factor that is quietly impacting the wine itself but one – psychology – that influences how we perceive it. 

Don’t look now – the power of autosuggestion 

The paramountcy of wine colour has been demonstrated in numerous studies; some have shown how easy it is to fool even wine experts simply by deliberately miscolouring a wine. The shape of the wine glass can be influential, as can the weight of the wine bottle. One analysis compared bottle weight and wine price and found that on average as the shelf price increased by £1, the bottle weight increased 8g. Put another way, for every additional £1 you pay you get an extra 8g of glass (a preconception The Wine Society is taking steps to counter with its lightweighting bottle initiative). 

Our taste perceptions are affected by a whole host of other factors, including the tasting ambience, our eating habits, medications, age, even our very genes. It’s perhaps surprising that there’s any consensus at all on wine tastes! But then, when we read a report on what an expert says a wine tastes like, given the suggestive psychological power of the placebo effect, it’s likely that’s what we will taste. 

> Read more on this The Mystery Of Minerality | The Wine Society  

> Caroline Gilby: The Science Of Taste | The Wine Society 

Taste the Limestone

Alex’s new book Taste the Limestone, Smell the Slate is available in hardback from academieduvinlibrary.com for £35 with a special 15% discount for members (quote WINESOCIETY15 at checkout).