The science and magic of wine- making

I grew up on tales of my Dad's 1970s
homemade hedgerow wines. Their
fruity aroma and potency were
legendary. All that remains of this
heady era are five very dusty bottles
of "vintage" wine sitting in my
father's garage. Of what vintage, or
even of what fruit these wines are
made, has long been forgotten. But
the bottles, and a glut of apples and
blackberries, inspired me to start
making my own wine. Beautiful
jewel-coloured liquids and the
constant plop of air locks have
formed a backdrop to my living
room ever since.
Many microbes are capable of
obtaining energy by consuming
sugars, and many liberate the alcohol
ethanol as a by-product.
Unfortunately for the microbes, they
are also producing their very own
poison. Ethanol will kill most
microbes even at low concentrations.
Fortunately for us, yeast is different.
It can survive in up to about 20%
ethanol before it is overcome, and
for millennia we have made use of
this ability in many fruitful ways.
The truth is that Dad's "vintage" wines
have taken the inevitable final step of
fermentation: their alcohol has
turned to vinegar. In fact it is
vinegar, not wine, that is God's gift to
man; all we can do is hold it a little
while at the wine stage.
It was only when we moved from
being hunter-gatherers to
agriculturists about 8,000 years ago
that we could accumulate enough
grapes for winemaking to begin.
From this point on grapes held sway
in winemaking because of the ease
with which they can be turned into
wine. Even the word "wine" has the
same ancient root as "vine".
However, almost anything can be
used to turn water into wine: fruits,
vegetables, flowers, spices, teabags –
whatever you think might taste good.
The recipe
Whatever ingredients you choose, the
basics are the same: get the right
balance of flavour, sugar and acid,
add some yeast, and away you go.
The following will work for most
fruits. For strong-tasting fruits like
elderberries use slightly less fruit (say
1.5kg). For fruit with gentle flavours,
such as apples and grapes, you can
use the pure juice (but then use less
sugar).
About 2kg fruit
1.5kg sugar
4.5L water
Packet of yeast (normally 5g)
Pectic enzyme
Lemon juice
Strong tea (alternatively, use raisins
or tannin extract)
Stage 1 - prepare the fruit
When making wine it is important to
control the microorganisms that
grow. Wild yeasts and bacteria exist
all around us and for much of the
history of wine were used to ferment
the fruit into alcohol. Unfortunately,
many of these will produce
unpleasant flavours and some can
make toxins. To ensure that only the
microbes you have chosen grow,
make sure you sterilise all your
equipment before you start.
To prepare the fruit, first remove any
stalks and leaves – you can remove
skins if you want but you will lose
lots of colour and flavour. Next,
crush the fruit in a large plastic food-
grade bucket. Sterilise the fruit by
adding boiling water to your bin. This
has the advantage of killing most
microorganisms but may affect the
flavour of the fruit. Alternatively, use
normal tap water and add a
Campden tablet . Invented in the
eponymous Cotswold village,
Campden tablets release sulphur
dioxide into the mixture. This will kill
most bacteria and will inhibit the
growth of most wild yeasts. The rest
will die later as the alcohol content
rises above 5%.
Allow the water to cool to below 50C
and then add some pectic enzyme.
Letting the water cool will avoids
damaging the enzyme, which breaks
down the networks of pectin
molecules that help hold plant cell
walls together. By breaking these
down, more juice is released and we
avoid the formation of "pectin haze"
in the finished wine. Letting the water
cool before adding avoids damaging
these little chemical factories.
Leave this mixture, or "must", for 24
hours to allow the juices to escape the
fruit and the sulphur dioxide to
disperse. If you add the yeast now,
the bubbles created can push fruit to
the top of the bucket and out of the
water, reducing flavour transfer.
Stage 2 – open fermentation
Before we can start fermentation we
need to add sugar to the must. The
type of sugar you use depends on
which kind of flavour you're after:
cane sugar, beet sugar and brown
sugar will all produce different
effects. Whichever you choose, the
yeast will work its way through the
sugar until it is used up or until so
much alcohol is produced that the
yeast dies. This recipe will give a wine
with about 13-15% alcohol. You are
now ready to add your yeast, the
miracle that makes wine work.
Once you have added, or pitched, the
yeast into the must give it a good stir.
Over the next 24 hours you can
watch as the calm wine-dark sea is
disturbed by bubbles of carbon
dioxide coming to the surface. Yeast
can live with or without oxygen but it
can create much more energy with it,
so we start our fermentation open
(but covered) to allow the yeast to
multiply and completely take over the
must.
As the yeast cells respire, a stormy
raft of bubbles will form and a dark
earthy smell will erupt from the
depths. You should leave this mixture
for 5-7 days in a warm place
(18-24C), stir it each day and watch
as the yeast makes it "boil". It is this
process that gives fermentation its
name, from the Latin word fervere,
"to boil". There are many species of
yeast but most winemaking is done
using the reliable Saccharomyces
cerevisiae. There are hundreds of
strains of C cerevisiae, each releasing
different flavours and surviving
different amounts of alcohol, so the
choice is yours.
In addition to sugar, yeast requires
various nutrients in order to flourish.
It needs amino acids, (poly)phenols,
various B vitamins, acids, and
minerals (such as phosphates).
Insufficient nutrients may result in a
"stuck" fermentation. Unfortunately,
most fruit does not contain all of
these nutrients and so additions need
to be made. Even commercial
vintners make nutrient additions,
although they don't shout about it.
While you can buy commercial
formulations, I have always found
that tap water, a cup of strong black
tea, and some lemon juice provide
enough nutrients for a lovely
fermentation.
It is also important to balance the
level of acidity in your wine. Acidity
gives tartness to your wine: too little
and you get a flat, lifeless wine; too
much and the wine tastes "sharp".
The optimum acidity of your wine is
about pH 4.5-5.5 and so for some
fruit you may need to add citric acid
in the form of lemons (up to three for
low-acidity fruits) or as tartaric acid
from raisins. Since citric acid is
partly used up during fermentation
tartaric acid will be a useful addition
for very low acidity fruits; it is also a
good yeast nutrient. Alternatively,
you could add a commercial acid
blend.
Stage 3 – fill the demijohn
Now that the yeast has gained a
strong hold over your must, we need
to seal it away from dangerous
oxygen – that which once fed your
yeast could now ruin your wine.
Removing oxygen forces yeast to
produce alcohol and stops bacteria
from turning that alcohol into acetic
acid, or vinegar. Transfer your must
to a sterile demijohn using a large
funnel and an old but clean tea-towel
to filter out the fruit pulp.
Once you've filtered it, have a taste.
Hopefully you have a sweet fruity
liquid with a hint of alcohol. If there
is any space left in the demijohn, fill
it up to just below the neck with clean
water. When the demijohn is full put
an airlock in the top; this will let the
carbon dioxide escape but keep the
oxygen out.
Stage 4 – closed fermentation
Left in a cool, dark place, your
cloudy, sweet liquid will gradually
turn into a clear, alcoholic one: a
fantastically pleasing sight,
accompanied by the hiccupping sound
from the airlock that lets you know
the yeast is still working.
Over the next few months, exhausted
yeast cells will sink to the bottom of
your demijohn, forming a deposit
known as "lees". These dead yeast
cells are digested by their own
enzymes and their "guts" get released
into the liquid, generating flavour.
However, if you leave this sediment
too long it will start to decompose
and release unpleasant flavours. To
avoid this, transfer the wine to a new
demijohn when there is 1-2 inches of
sediment at the bottom. This is called
racking. You might need to repeat this
several times, but ensure that you
always carefully minimise contact
with oxygen. Top up with clean water
after each racking.
After about nine months the
fermentation should finish, the
bubbling should come to an end, and
the wine should be clear. You can
check the yeast has finished
producing alcohol by moving the
demijohn to a warm place for a few
days to see if that wakes it up.
Stage 5 – bottle
Bottling is a dangerous stage when
your wine can catch "the wine
disease" and turn to vinegar. To
avoid this, Pliny suggested adding tree
resin; later winemakers found that
adding brandy helped prevent it and
so invented sherry. We now know
that it is bacteria that cause the
disease and we can stop them with a
Campden tablet. The sulphur dioxide
released into the demijohn will kill
the bacteria and also act as an
antioxidant during bottling.
You are now ready to bottle your
beautifully clear wine. Siphon it into
sterilised bottles, being careful not to
carry sediment over. I always put my
new wine into old bottles. You'll need
six.
This is another tasting opportunity:
run some of your "nouveau" wine
round your mouth. Is it fruity, sweet,
tart, or astringent?
Stage 6 – ageing
One of the appeals of wine is that left
in a cool dark place it will
continuously change. Flavours and
aromas will develop and improve.
Unfortunately, the process is very
complex, so it is not possible to
predict from bottle to bottle when
flavour and aroma will peak. There
are interactions between hundreds of
different compounds, all of which
contribute towards the ultimate
flavour, aroma and structure of the
drink.
One set of such compounds are the
tannins. Tannins are the third most
important feature of a wine's flavour
after sweetness and acidity. They are
phenolic compounds that are
common in darker fruits such as
elderberries and red grapes,
especially in the skins. They bind to
the proteins in our saliva, inhibiting
its ability to lubricate the mouth,
causing a puckering, astringent
feeling.
Some fruits, such as strawberries,
lack tannins and so do not have the
"mouth feel" of good wines; for these,
tannin-rich black tea is an important
addition. As wine ages, excess tannins
slowly bind together in long chains
and fall to the bottom of the bottle as
sediment, allowing the wine to
mellow. The more tannins in your
wine, the longer you'll have to age it.
For example, elderberry wine might
need two years before the tannins
mellow and it reaches its peak. I
leave all my wines for at least six
months before I take a sip to see
whether it is ready to share with
others.
Stage 6 – drink!
Few things compare to the pleasure of
sharing a glass of your homemade
wine with your friends while plotting
how you are going to fill your next
demijohn. I hope that your wine will
be the finest wine known to humanity
… or at least your corner of it