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Whats a Botrytis

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					What's a Botrytis, Noble Rot Or Late Pick Wine?
Botrytis bunch rot or grey mould is a disease that exists in all
vineyards worldwide and is caused by the fungus Botrytis cinerea.
Botrytis can hit grapes at any time but the most common infection time is
when they are very nearly ripe. Botrytis bunch rot stays alive during
winter on the bark, in dormant buds and in debris under the vine. That's
just one reason to keep the vineyard clean. Botrytis spores are produced
in spring and infect leaves and berries. Water is required for
germination and long periods of wetness with high levels of humidity are
ideal spore production conditions.
An infection period during spring will kill off the flowers and/or the
berries on the vine. This means a vastly reduced yield. Instead of the
full number of ripe berries on the bunch we may be getting only 50%. Any
break in the skin of the berry from birds, wind, splitting due to hail or
sunburn provides an easy infection entry point. Eventually the entire
bunch becomes a grey mouldy mass of spores. In dry weather the berries
dry up and there's very little damage further on. During wet wether the
berries burst and spread the mould further.
We manage botrytis in the vineyard in two ways: environmentally and
chemically.
Environmental management includes changes done to maximise the airflow
around the vine canopy to decrease humidity. Different trellising,
pruning and leaf plucking methods are used to manage the canopy density.
Everything possible is done to minimise berry splitting. We go to great
lengths to keep the weeds down under the vines and the ground as clean as
possible as botrytis can survive on vine prunings and even weeds.
Chemical management involves sprays to kill the fungus before it
multiplies rapidly or 'blooms'. Wet humid weather is the danger time when
we have to monitor the vineyard daily and spray regularly. Flowering and
'bunch closure' (when the bunch rapidly fills in, late spring to early
summer) are the two crucial periods.
Legend has it that in 1650 a priest had his harvest delayed when the
Turks attacked. When they returned to the harvest they found a fungus had
grown on some bunches. They wondered what the wine made from these grapes
would taste like and were pleasantly surprised. The Germans and then the
French were next to follow with the botrytis or 'noble rot' wines. The
best grapes for noble rot wines are Riesling, Gewürztraminer, Semillon,
Sauvignon Blanc and Chenin Blanc.
The botrytis fungus will puncture the skin and slowly draw out the
moisture from the grape. This produces grapes with much less liquid than
normally ripe grapes and consequently a much higher sugar concentration.
Grapes are carefully harvested. The harvest may occur in stages. One pass
will pick up the ripest grapes. You then wait for a few days and harvest
again to pick up only the very ripest grapes in the block. If you leave
it too late you can smell the vinegar walking through the vineyard. Then
you know you've left it too late. You have to pick the grapes while
they're still moist raisins, not when they've dried up.
Needless to say this is a very slow and precise process. You definitely
can't machine harvest a botrytis crop. The very rot that you are fighting
off for most of the year is what you desperately hope for in the final
weeks and days of harvest.
The term 'late pick' is used synonymously with botrytis wines but is not
the same thing. Late pick means just that. The fruit is left on the vine
to very slowly ripen and wither on the vine. The same concentration of
sugars that happens with 'noble rot' happens naturally in late pick
grapes. The botrytis infection just helps speed up this natural process.
The harvest is delayed while the grapes literally wither on the vine
producing almost raisins with incredible sugars and favours.
If all the sugar in these grapes were fermented we would get a wine of
around 20% alcohol content. However, the yeasts used to start the
winemaking process will die when the alcohol content reaches around 15%.
This leaves a beautifully balanced wine with good crisp acids, plenty of
sugar for sweetness and lots of alcohol. An environment of approximately
15% alcohol content by volume becomes toxic to the yeasts. Normally the
yeasts would happily continue multiplying and consuming sugars until they
ran out of food. In the case of botrytis wines the yeasts do their job so
well that they produce a toxic environment for themselves.
In the winery the grapes are hard to work with. The juice flows like
molasses, not like normal grape juice. The pumps are wo rking harder and
everything is sticky. The botrytis grapes are always the last ones to be
picked so they're coming through when the winery has been cleaned up
after harvest. Almost an afterthought.
But when you open a sweet bottle of 'noble rot' wine, all the troubles
are truly worth it.
And, an interesting point. In Australia it is illegal to add sugar to
wines. We can add acids (tartaric, citric etc) but not sugars. In the
rest of the world it's the other way around. You are allowed to add
sugars (chaptalisation is the winemakers term for sweetening wines by
adding sugar) but you're not allowed to add acids.
Keep any eye out for these wines as they are wonderful addition to any
meal or any evening. If you haven't tried any, make sure you do as you
are missing out on some wonderful drinking.
The Gurdies Winery is one of Australias premium cool climate wineries.
The weekly newsletter gives you a snapshot of 'This day in wine history',
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website http://www.thegurdieswinery.com.au or send a blank email to
whatson@thegurdieswinery.getresponse.com

				
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