Thursday, February 04, 2010

Vintage 2010

Harvest is dependent on the ‘ripeness’ of the grapes. Ripeness can mean a number of things. Sugar ripe is when the grape juice has reached a certain sugar concentration. Sugar level of the grape juice determines the eventual alcohol content of the wine. Flavour and aroma ripeness is when the taster of the juice determines that the juice has the potential to produce wine that will have the necessary varietal characteristics. Phenolic ripeness refers to the changes in the tannins that occur in grape skins, seeds and stems. The ‘ripe’ tannins become less bitter tasting and softer, and the methoxypyrazine levels decrease, making the grapes (and resultant wine) taste less green or herbaceous, particularly important in red wines.
Phenolic ripeness lags behind sugar ripeness and in warm climates, like ours, it is important that we keep an eye on both. We know that we normally achieve adequate sugar ripeness and generally don’t want to produce ‘big’ alcoholic wines so it’s important to watch the tannins closely and not let the grapes get too sugar ripe.
How do we go about monitoring this situation?
We know from experience approximately within a few weeks when the grapes should be ready. At first we walk the rows randomly selecting berries from bunches and testing them separately on a refractometer for sugar levels just to get a feel for the overall state of the vineyard. Later, in addition to this, we start tasting the grapes, inspecting the stalks for colour change and looking at and ‘cracking’ the seeds. Finally when we believe that harvest is imminent ie. when we think the phenolics are ripe, we take a sampling of grape berries from the whole vineyard in quite an organised way eg. every 4th vine, a berry from the back, front, top and bottom of a bunch, crush them and sugar test the juice either with a refractometer (right) or alternatively a hydrometer (centre 2), just to confirm sugar ripeness.

At this stage we usually look at acid levels, mainly pH, with a pH metre (left) as well as titratable acidity (TA). But as these two can be adjusted during the wine making process with acid additions it is not that critical.
Sugar levels in grape juice are determined by a number of scales which are based on the SG (specific gravity) of liquids where distilled water equals 1.0. Grape juice is basically a solution of water and sugar (fructose + glucose). The higher the SG, the denser the liquid thus the higher the sugar content.
Other scales include Oechlse, Baume and Brix where 1.1 SG = 100 Oe = 13.1 Baume = 23.7 Brix.
Measurements are temperature dependent and needs to be accounted for.
I like Baume because it indicates the potential alcoholic content of the wine after fermentation.
But I always use SG to determine when fermentation is finished ie. when all the sugar has been converted into alcohol by the yeast as the SG of the solution is then usually less than 1.0 and a SG hydrometer is a little more accurate at those low levels.
So that is where we are at the moment, waiting for the weather to clear a little (yes! It has been raining) so we can get into the Pinot Noir, which is ready, and start Vintage 2010.

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