Water of life, without water
Chemists
have figured out an answer to that hoary old chestnut - water or not, when
drinking whisky. John Piggot, from the University of Strathclyde, Scotland,
unlocks the chemical secrets of perhaps the most complicated alcoholic
beverage in the world and comes down in favor of personal taste. Whiskies,
whether Scotch, Irish, Bourbon, Kentucky, or moonshine, contain hundreds of
compounds, including fatty acids, esters, alcohols, and aldehydes, in a wide
range of concentrations. Apparently, adding water to whisky does indeed
release some flavors, but masks others, while not adding water masks nothing
but reveals no additional aromatic notes either.
Is
this the most chemically complicated drink in the world? Victoria Gill
attempts to unlock some of the mysteries of Scotch malt whisky
The finely-tuned process of Scotch whisky production is
governed by its own law - the Scotch Whisky Act
·
There are 92 malt whisky distilleries in Scotland, and
each one has a slightly different process - with different stills, malts and
casks for maturation
·
Under the Act, Scotch whisky must be matured for at least
three years, during which time the spirit reacts with compounds in the timber
casks
·
Chemists continue to study the complex effects of dilution
on the sensory perception of whisky flavours
When
I worked in a tiny Edinburgh pub, I occasionally incurred the wrath of the
regulars when the water jug sat on the bar wasn't at room temperature by the
time they wanted their whisky. So I've long been eager to find out if there's
any chemical truth behind this received bar wisdom, and similar whisky lore.
I've
heard much postulating about 'releasing the flavours', so during my visit to
Edinburgh's Scotch Whisky Research Institute (SWRI), I hoped the real experts
might teach me how to make it - or fake it - as a whisky connoisseur, so that
I could smugly explain to my friends in the pub exactly how one should dilute
one's whisky - and more importantly, why.
But
embarking on a whirlwind tour of whisky chemistry raised far more questions
than I could have predicted. Like the heady, aromatic spirit itself, it's far
from simple. There's no single chemical composition to describe a whisky, so
there's no single way to explain what exactly happens in your glass when you
add water, ice or even (heaven forfend) cola.
Making
flavour
Whiskies
contain hundreds of compounds, including fatty acids, esters, alcohols, and
aldehydes, in a wide range of concentrations. According to Paul Hughes,
director of the International Centre for Brewing and Distilling (ICBD) at
Heriot-Watt University in Edinburgh, the most important flavours in a whisky
come from 'the raw materials, the distillation process, and the maturation'.
So that's the whole whisky-making process, then - and there's just no
narrowing it down.
To
begin at the beginning, we need to go back to the raw materials. That's
Scotch whisky 10, 12, 16 or more years before it's poured into your glass.
The Scotch Whisky Act quite literally lays down the law about raw materials
and the production process.1 Scotch malt whisky is made from
100 per cent malted barley - grain that has been germinated very briefly,
releasing the enzymes that convert starch into the sugar that eventually
becomes alcohol.
Whisky-producers
start with a mash of malt and water. (Under the Act, distillers must use that
water as it arrives at their distillery, untreated in any way). The aim is to
turn as much of the grain's starch into sugar as possible, for the highest
alcohol yield.
The
strong sugar solution is taken from the mash, and yeast is added for
fermentation. This takes about 72 hours, after which the alcoholic solution -
or wash - goes for distillation.
This
is where those impressive, bulbous copper stills come in. Distillation is
essentially very simple - heating the mixture to separate it into fractions
based on their volatility - although the copper also catalyses some important
reactions on the side. And as with any scaled-up process, there are a lot of
variables. Reflux, for example, is determined by the neck of the still, so
its shape is very important, and each distillery designs its own.
'Copper
catalyses the reactions you want most in distillation - especially those
reactions that remove sulfurous compounds,' explains Craig Owen, a chemist
and laboratory manager at the SWRI.
The
research at the SWRI is funded by its members - Scotch malt whisky
producers -who are constantly refining the efficiency of their
processes. 'What distilleries are looking for is continuity,' says Owen.
'They want to understand each part of the process, so that if anything starts
to drift they know exactly where the problem will be - to get it back on
track again.'
Distillation
of the spirit gives three fractions - the foreshots that contain the highly
volatile components such as acetaldehyde and ethyl acetate, the spirit
fraction that will go on to be matured into Scotch, and the feints which
contain the low volatility compounds, including phenols and many
nitrogen-containing compounds. Foreshots and feints are removed but, since
they contain alcohol, they are recycled and redistilled.
'Most
Scotch whisky is distilled twice,' explains Brian Eaton, senior teaching
fellow at the ICBD. 'That's a key difference between Irish whiskey and
Scotch. Irish whiskey is triple-distilled, and that's a big marketing point -
its purity. But the thing about double-distilling is the flavour compounds
that remain in the whisky. You could say that the aim with Scotch whisky is
to distil it just enough.'
The
spice of life
There
are 92 malt distilleries in Scotland, all unique. Each takes a slightly different
fraction during distillation - so each spirit is chemically different before
it even gets into the cask to mature. This colourless liquid already contains
some of the compounds that are evident in the final flavour - phenols,
esters, lactones, aldehydes some sulfur and nitrogen-containing
compounds.
But
the cask is where the really interesting stuff happens - with the maturation
process finely tuned to each individual whisky. 'When you mature a Scotch,
you're trying to balance the spirit character with the maturation character,'
says Eaton. 'Some may be matured for eight years, but most of the very smoky
malts are matured for 12 to 16 years - because it takes longer to get the
balance right.'
Most
casks are made of American white oak, and have already been used once to make
bourbon. 'The American bourbon industry uses new casks every time, so it's a
cheap and efficient way to buy them,' says Eaton. Bourbon-making is also a
good pre-treatment for the casks. White oak contains a lot of vanillin - the compound
responsible for the sweet, vanilla note that is a signature of bourbon.
Making bourbon extracts a lot of the vanillin from the casks, and only then
are they ready for Scotch.
All
casks must be less than 700 litre capacity, because much of the maturation
chemistry depends on good contact with the wood. Three types of reaction
happen in the cask - additive, subtractive and interactive. In subtractive
reactions, compounds are lost through the timber - including the pungent
sulfur compounds, such as dimethyl sulfide.
And
as oxygen diffuses into the cask, reactions take place between the molecules
in the spirit, and between the spirit and the wood. Alcohols and aldehydes
are oxidised, and acids react with ethanol to form esters - which are some of
the most aromatic of whisky flavour compounds.
The
casks are often fired to char the inside. The resulting layer of active
carbon on the inner surface removes some unwanted compounds, and charring
starts the breakdown of lignin in the wood.
'Lignin
undergoes what's been termed ethanolysis,' says John Piggott from the
University of Strathclyde. 'Ethanol reacts with the lignin to break it down
into some of the important flavour compounds, such as aromatic aldehydes.'
Piggott has compared charred with uncharred oak in the maturation of Scotch
malt whisky, and found that charring increased the production of whisky
lactones (cis - and trans -methyloctalactone)
- fruity flavour compounds often described as smelling like coconut.2
And
it's maturation in timber casks that gives the whisky its golden colour.
Melanoidins - from the breakdown of cellulose - help to brown the spirit. And
some distilleries use old sherry or rum casks, which also darken the whisky,
as well as contributing to its flavour. The only additive allowed, apart from
water, is caramel, which can be added to bring the whisky to a standard
colour.
Smoky
notes
Not
all distilleries smoke their malt - but some, including Laphroaig, Ardbeg and
Lagavulin, all on the Scottish island of Islay, are famous for it. It's a
practice derived from the days when people would dry out their malted barley
over a peat-fuelled fire, simply because peat was an easily and locally
accessible fuel. Phenolic compounds transfered from the peat give these
whiskies their signature smoky flavour.
But
even peat chemistry is complex. Barry Harrison, a distillation researcher at
the SWRI, has studied different peats and found that the chemical composition
of a peat bog depends on its geographical location. 'So I tried to find out
if we could match that to chemical fingerprint of the spirit,' says Harrison.
He
dug peat samples from six locations across Scotland - three of which were
peat bogs on Islay. 'I smoked malt in the fume cupboard in a lab, then
distilled my own spirit with it.' Harrison used a combination of analytical
techniques to study his peat samples and smoked malt, and even volunteer
nosers to test his lab-made spirit.
He
found not only that peat from different bogs could be distinguished by its
chemical fingerprint, but that the chemical fingerprint of a bog was still
distinguishable in the final spirit. It's just one example of a practice
steeped in tradition that plays a part in the mysterious chemistry of malt whisky.4
Age
is everything
The
Act states that whisky is not Scotch whisky until it has been matured for at
least three years. And that it must be matured in Scotland. 'This isn't the
industry being protectionist,' says Eaton. 'It's down to the climate - it's
cold and damp, which affects maturation. In the US, the ethanol concentration
in the cask goes up because it's hot and dry, here it goes down.'
Once
a whisky has matured, it is blended and diluted for bottling - cask strength
whisky can be more than 60 per cent ethanol, and the final bottled spirit is
40 per cent. Each distillery has a master blender - a person able to detect
hundreds of flavour compounds by nose alone. This is still a talent no piece
of analytical equipment can match, and everyone interviewed for a job at the
SWRI is asked to take a smelling test to see if they could join the
institute's panel of 19 nosers.
Single
malts are usually blended from several casks - all from the same distillery -
to establish just the right flavour. The age on the bottle indicates the
youngest whisky in that blend.
Eaton
says the belief that single malt whiskies are far superior to what we
commonly refer to as blended whiskies is something of a misconception. 'From
around 1890 to the 1960s everyone drank blended whisky,' says Eaton. The late
1800s are significant because an aphid-related pest called phylloxera,
accidently imported from America, had wiped out the grapevines across France
and the rest of Europe.
'People
in the UK who drank brandy couldn't get it, so they looked to Scotland where
they were making this very fiery spirit called malt whisky. This was too
strong for most people, so they started making grain whisky - distilled from
a mixture of whole grain cereals, usually wheat or maize, and the malted
barley that produces the necessary enzymes.
'Grain
whisky is distilled to a higher alcoholic strength, and it is blander. By
blending the grain whisky with the malt whisky, they made a spirit that was
acceptable for the would-be brandy drinkers in the UK to have as an
after-dinner drink. So people started drinking blended whisky.'
It
was only when the first single malt was marketed by Glenfiddich in the 1960s
that single malts became more widely available. And today they represent
about 5 per cent of the whisky market.
'In
a single malt you get a narrow band of flavour - peaty, waxy, meaty sulfur,
grassy - so if you like that flavour, you find the malt that's to your exact
taste,' says Eaton. 'A blender may take 35 different malts and two to three
grains, and blends them to give all the different characteristics. People
think blends are cheap and nasty and they're not, many of them are
superb.'
How
to drink whisky
Just
as diverse and complex are the ways in which whisky is consumed. But single
malt purists will often tell you to add just a little room temperature water.
So is that the 'right way' to drink whisky?
'It's
personal preference - there are no instructions on the bottle that say
"dilute to taste",' Owen points out diplomatically. 'It's partly
about practicality. When we're nosing the whisky, it's diluted to 20 per cent
[ethanol concentration] because at 40 per cent, after nosing a few whiskies,
you wouldn't be able to smell anything.' Since the whisky producers rely very
much on teams of nosers for their quality control (whisky producers' master
blenders often have their olfactory equipment insured for large sums)
avoiding numbing the nosers' precious noses is very important.
'With
sprits, there's a magic dilution of 17 per cent where you have a continuous
phase of water and ethanol,' adds Hughes. 'Otherwise you get some clustering
- pockets of ethanol where the more ethanol-soluble compounds will
gather.'
Perhaps
this is something I can finally quantify - you need just the right amount of
water to bring the spirit to this continuous phase. But, as always, it's far
more complicated for Scotch, as Hughes explains: 'Whisky is not ethanol and
water alone. Once you start to introduce all the other components, the simple
dynamic of ethanol and water mixtures is affected. So it's much trickier to
put a critical dilution on whisky.'
Piggott
has tested the influence of dilution on the sensory impact of a whisky. His
team at Strathclyde measured the compounds occupying the 'headspace' above
the whisky - that's the part you stick your nose into to take in all of those
aromatic notes. And dilution, it seems, is not just about the oft-quoted
release of flavour compounds - it releases some but masks others.3
'If
you increase the water content, you reduce the solubility of some long-chain
compounds - such as esters,' he explains. 'You also increase the volatility
of some compounds, especially hydrophobic ones. While phenols, for example -
the smoky compounds - are particularly water-soluble, so you'd expect to
reduce the volatility of those as you dilute. Nitrogen-containing compounds
too - they're the roasted nut and cereal flavours - would be reduced.' So if
you like the cereal tones or that smoked peaty aroma, drink your malt whisky
neat.
And
the insistence upon room temperature water? 'Ice or very cold water will
reduce the volatility of many flavour compounds - it keeps the flavour in the
liquid, so you may not get the aromas, but you'll still get the taste,' says
Hughes.
One
guaranteed effect of dilution for every whisky is that it diminishes the
ethanol concentration. But whether that reliably reduces the alcoholic burn
depends, once again, on the whisky you're drinking. 'If you dilute to 20 per
cent ethanol, you reduce the pungency, so for younger spirits that would seem
to be a good idea - to get more out of the rest of the flavour. But something
very strange goes on as whisky matures.'
Piggott's
experiments have shown some whiskies are not as pungent as they should be
given their ethanol concentration. 'If you plot the amount of ethanol in the
head space against pungency [detected by nosing], you would normally see a
direct correlation. But we found that some whiskies were less pungent than
they should have been - and that seemed to tie in with maturity, which links
with the popular view that you should drink well-matured malts
neat.'
'At
tastings at the Scottish Malt Whisky Society, they tend to taste
cask-strength whiskies, diluting them to taste,' says Hughes. 'When you add
water to one it tastes much better, but add water to another and it might
taste far worse. For example, heavier whiskies that have strong sulfur
notes -those compounds are released when you dilute the whisky, and most
people find them unpleasant.'
Only
Hughes will be drawn on the best way to drink a whisky, and his advice is
surprisingly specific. 'The master blender at the Talisker distillery once
told me 18 year old Talisker with vanilla ice cream and pepper was the best
combination,' says Hughes. 'I just wonder how on Earth they found that
out.'
'Blue
cheese or chocolate often go well with whisky,' says Owen. 'But it's entirely
down to personal taste. In China it's often mixed with green tea. In Spain many
people drink it with a mixer, like cola.'
And
according to one well-known Scottish joke, that's actually the only way to
drink the stuff - cola, that is.
Chemweb.COM
|
Saturday, May 28, 2016
WHISKY SPECIAL ......Water of life, without water
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