In the July
edition of
Societynews
we answered
a member’s
question on
the term ‘minerality’. Here
Master of Wine and scientist
Caroline Gilby examines the
subject in more detail
Back in the late 1990s, I recall doing
some translation work for a Chablis
producer when I insisted that ‘the
typicity of the minerality’ was a
meaningless phrase in English. The
word ‘minerality’ barely appeared in
wine language back then and it didn’t
appear in Emile Peynaud’s legendary
wine tasting bible The Taste of Wine
published in the 1983. Today, though,
you won’t read many wine descriptions
before the words ‘mineral’ or
‘minerality’ crop up (‘mineral’ appears
more than 50 times if you do a search
on The Wine Society website, for
example). It’s usually a positive cue
for a quality wine with a sense of place
or terroir and often linked closely to
a specific soil or rock type.
> Classic 'mineral' wines to taste
But does minerality come
from the soil?
There is an implication that this
mineral quality must somehow come
from the vineyard and the soils or
bedrock, but try as they might
scientists cannot find any sort of
mechanism for this. The thing is that
plants are very good at absorbing what
they need and nothing more. And it’s
important to understand that in fact
what they take up from the soil
through the roots has to be dissolved
in water, meaning very simple ions,
and these have no taste at the levels
measured in wine. There’s a good
paper by Alex Maltmann of
Aberystwyth University on this for
anyone wanting to delve deeper.
It makes no difference whether a
calcium ion, for instance, comes from
chalk, limestone, clay or any other
sort of bedrock – it’s still the same
tasteless cation. And there’s no
mechanism for complex or crystalline
minerals to be taken up by plant
roots and end up in the grapes.
At this point it’s worth a couple
of definitions. The International
Mineralogical Association definition is
‘A mineral is an element or chemical
compound that is normally crystalline
and that has been formed as a result
of geological processes.’ It is also
naturally occurring (so not man
made), inorganic, solid with a definite
chemical composition and ordered
internal structure. In contrast, rocks
are disordered and are a mixture of
minerals. Examples of minerals include
things like calcite (that is important in
limestone rock), halite (rock salt) and
sulphur, while rocks include chalk,
slate, shale, basalt and many more.
Distinctly different: halite (rock-salt) is a mineral not a rock
Do we all mean the same
thing when we use the
term ‘mineral’?
The use of the word ‘mineral’ has
become so widespread that various
researchers have tried to identify if
there is a detectable cause in wine
and indeed if there is any unity
between tasters in what the concept
of ‘mineral’ or ‘minerality’ means.
One recent paper by Parr et al in
New Zealand tested two groups of
tasters from France and New Zealand
respectively to identify mineral
characters in samples of sauvignon
blanc. Descriptors like citrus, flinty
and chalky were linked to minerality in
both groups while tropical notes like
passion fruit were negatively linked to
minerality. Interestingly, in this group
the French tasters relied more heavily
on the nose to evaluate wines than
the New Zealand ones though there
was largely agreement about key
descriptions. Parr has also pointed out
that the rise of the term ‘minerality’
has also been paralleled by the rise of
screw cap use in New Zealand.
Are some grapes more
likely to be described as
‘mineral’?
Chardonnay, one of the grapes more prone to show mineral characteristics
If you ever get the chance to do a
horizontal tasting across wines from
different soil types from a single
producer, it’s clear there are
differences and therefore also clear
that there’s a gaping chasm between
the art and scientific understanding of
this aspect of wine. But scientists are
working hard to try and tackle this.
A recent study in Spain (by Outlook
Wine and Excell Iberica) entitled
Minerality in Wines found that the
chemical composition of wines and
perception of mineral characters are
not linked to minerals in vineyard soil.
The team also looked at the sensory
basis for mineral character in wine
and came to some conclusions. They
found that certain grapes are more
prone to showing mineral character
including chardonnay, chenin blanc,
albariño and sauvignon blanc, and in
reds syrah and pinot noir with
cabernet franc, nebbiolo and cabernet
sauvignon to a lesser extent.
Cool climate means more
incidences of ‘minerality’?
There was also an association with
expressing ‘minerality’ if grapes had
been grown in cold or cool climates;
harvested earlier rather than fully or
over-ripe; if the wines showed high
acidity/low pH and had been made
using reductive techniques (ie minimal
exposure to oxygen) and had higher
levels of free sulphur dioxide. They also
found that there had to be an absence
of highly aromatic compounds, particularly terpenes (responsible for
key aromas in lemons, lavender and
pine, for instance) and fruity esters. The
researchers also found the presence of
higher levels of an acid called succinic
acid (which is produced by the yeast
metabolism during fermentation) and
has a salty taste is directly associated
with the concept of minerality in some
wines. However, careful research to
define a group of wines as ‘mineral’ and
then to analyse them, did not find any
single compound consistently linked to
this characteristic.
Vineyard characteristics
could have some influence
What is clear is that this is a complex
picture and there are almost certainly
links with what is going on in the
vineyard and its soils, even if the soils
are not involved directly. For instance,
stress in the vineyard caused by lack of
water (on sandy, gravelly or rocky
sites, for example) can cause changes
in juice composition that may lead to
‘mineral’ characters. Another soil
factor is that infertile soils with low
nitrogen (limestone soils are often low
in fertility, for instance) may mean low
nitrogen in the juice which can force
yeast to metabolise more sulphurcontaining compounds, leading to
more reductive, struck-match/flinty
characters associated with ‘mineral’
descriptions. This suggests that
geological/climatic factors are involved
but doesn’t show any firm link with an
identifiable chemical. The process of
fermentation plus clarification and
stabilising wine also affects the
composition of wine and thus its final
taste and possible perceptions of
‘minerality’ too.
Stress in the vineyard due to lack of water may lead to ‘mineral’ characters (Rocky vineyard, Croatia)
So, the answer doesn’t just
lie in the soil then?
So it appears that the phenomenon
of ‘minerality’ is complex and most
likely to be an indirect effect of grape
growing and also winemaking. But it
is not in any provable or literal way a
taste of actual rocks or minerals found
in a vineyard. Nonetheless, the word
‘mineral’ has become very fashionable
and a handy shorthand for implying
quality, elegance and provenance.
I don’t see the word going out of
fashion anytime soon.