Let me start on this note, if you are in this trade you have heard an awful lot of tales along the line. For example, a Manzanilla taste salty because the bodegas, where they are aged, are on the seashore and consequently closer to the salty sea winds than Jerez where they age Fino! Therefore, the wind imparts the salty flavour. I wonder why port does not taste salty then. Another interesting one, that I have also heard, was that certain wines have a fruity apricot flavour profile because the vinyard is situated next to apricot orchards. It sounds lovely and quite wonderful, but not true. So, beware and have your doubts.
I am confident that anybody who ever read or written any kind of wine description, myself included, or attended a tasting, come across the mystical term: minerality. It has been used, over-used and abused to an exceptional degree. We all seem to understand the certain quality, flavour compound that we are referring to when we use this descriptor. What do we really mean when we using it? Difficult to tell. I have heard well-regarded Master Sommeliers and laymen talking about it alike, but when you start asking questions the answers seem to be quite confusing and more often than not, lacking any scientific thinking or evidence. Is it not just a myth, a story, a fable we like to tell that we are able to taste the soil the grapes have been grown on in a glass of wine?
When I was doing my WSET courses, we were always cautioned not to use this particular term, but on my CMS course, even Master Sommeliers were a bit unsure, and claimed they were not convinced just yet whether that minerality as a quality in wine came from the specific soil or not. It is most certainly true that different soils have a flavour altering effect on the same grape variety even if they are next to each other. You can find plenty of examples from Burgundy to Bordeaux. My argument is that it has a less of a direct effect. In other words, a good Chablis does not taste flinty and steely because it was planted on flint and steel.
At first, if you care to spare some thoughts what a plant, any plant can actually take up from the soil will shed some lights on the problem. Plants on your windowsill, potted or otherwise need watering. That suggests that they can use minerals dissolved in water via capillary effect. Stones rarely melt into water naturally, although some of its mineral content could be dissolved into natural waters, but the constant flow of a river does not equal with watering or rain. You cannot dissolve sand in water, otherwise it would be quite troublesome solution as a flood defence. Of course, there is a natural weathering down, but it is very-very-very slow. So much so that the amount of minerals exclusively derived from this process would not be sufficient to a plant. That is why humus is needed in the soil. That is why fairly frequently you put some compost in your garden or refresh your potted plants. You do not tend to put stones in your garden as source of minerals as you would find those stones intact after many decades.
If plants take up minerals dissolved in water, those minerals must be in atomic or more likely ionic form to be able to disperse. Can you recall how ions like Ca2+, Mg2+, K+ taste like? Have you ever experienced it? These ions are the building blocks of mineral compounds and not the actual type of rock. Whatever flavour they have, if any, it surely cannot be the same as those infamous stones the plants have been in contact with. Incidentally, the only mineral that humans can identify easily in a solution or otherwise is salt. Not to mention that those ions are in the wine in minor quantities with alcohol, sugar, extracts, acids and other flavour compounds, and you still able to detect them clearly down to the specific type of rock? Sounds quite unbelievable to me. Just as a comparison, sugar can be detected in wine, if you are a good and well-experienced taster, when there is at least 2g of sugar in a litre of liquid. (Apropos, you are quite skilled on how sugar taste like.) Sometimes when you taste wine with particularly high acidity, like a dry Riesling, there can be even 7-8g residual sugar in a litre of wine and you would still get the impression of being dry without a hint of sweetness. Here we are talking about micrograms or even smaller amounts of dissolved ions that has been used up by the plants for photosynthesis to be able to support grape growth. Those grapes have been collected, crushed, pressed than fermented, sometimes aged in oak. In other words, a staggering amount of chemical interactions happened to them. To be able to identify the original source, like gneiss, slate or limestone, it is not short of a miracle.
It is important to note as well, that vine tends to prefer well-draining and poor soils and not fertile ones, so you do not need huge amounts of minerals and trace elements. It is commonplace that the best wines of the world coming from vineyards with limestone in the make up of the soil. Fact! Just think about, Chablis, Champagne, Burgundy, Rioja, Barolo. Also, a botanical fact that plants and grapes in particular, not very fond of lime in the soil as it is altering the PH of the soil and causes chlorosis. A disease that makes the plant struggle to take up iron from the soil, that leads to loss of chlorophyll pigments that slows down photosynthesis and can lead to plant death. That is one of the reasons vines are grafted on certain types of rootstocks to cope with lime rich soils. So why are we appearing to be able to tell if a good Sancerre has a lovely gunflint quality to it? (Again, there is no gunflint in the soil in Sancerre.) Or why we can experience a lovely petrol (mineral oil) scent in good old Rieslings and Semillons? Most certainly not because they have been planted over petroleum fields. Why we cannot taste minerality in grapes or in must? You should be able to if minerals flavouring liquid to such an extent. How come this magical flavour only seems to appear in fermented must and not necessarily in every one of them either. White wines tend to be more likely to have a much more pronounced minerality than reds. It may have to do something with fermentation temperatures. Red wines are fermented in much higher temperatures than whites. New World whites tend to be fermented on the lower end of white wine fermentation temperatures usually inoculated as well whereas in the Old World it is more like the middle or the higher end and not necessarily using cultured yeasts.
Although the soil is of utmost importance when we talk about wine, the different qualities those types of rocks represent physically may influence grape growing physiologically. Grapevine does not like to be water-logged. Limestone rich soils and gravelly soils are particularly well-draining. Stony soils usually quite poor as well, which again can come handy for vine. They do hold temperature well that supports steady ripening. These factors can add up making a difference how a wine taste like from individual vineyards and we should not forget about the very important role of the winemaker.
Photographs by The Tannin Addict.