But how do we decide when the vintage starts? In order to maximize wine quality the grapes need to have reached a certain level of development on the vine. This is determined by a set of precise measurements and observations. When you have been growing wine grapes for a while, you get a reasonably accurate idea from taste alone, of when they are ready for winemaking. Grapes are very palatable to eat some weeks before this, but at this stage respective levels of sugar and acid will make a rather thin and sour wine, with a low level of alcohol.
Taste alone is not generally good enough. The when-to-pick decision for most of us is made after we have collected a sample of grapes, examined the pips and stems, juiced the fruit, measured the sugar level, either by refractometer or hydrometer, measured the pH, then measured the level of acidity using a laboratory process called titration, which involves progressively adding an alkaline solution to the juice until it raises the pH to a particular level. The amount of alkali added is the measure of how much acid is in the fruit. In popular mythology the sugar level or “brix” is considered the key determinant, but getting the acid down is just as critical as getting the sugar up, possibly more so with red wines.
It is particularly important that the test sample is thoroughly representative of the area to be picked, because not every bunch or every berry within a bunch is at the same level of development. Some are well exposed to the sun and will be advanced in their ripeness, while others will be partially or fully shaded by leaves, and others will be in rows near shelter belts which may mean they receive less sun and will be less ripe. So the criterion for picking is the average ripeness of the complete area to be picked.
When to pick may be complicated by what the weather is doing or has done in the recent past, so for example significant rain events around this time can cause consternation and gnashing of teeth. And after the picking decision is taken the winemaker immediately has a range of other issues to consider and decisions to make, but that is another subject…..
Robin Ransom
President, Matakana Winegrowers Inc.
robin@ransomwines.co.nz
Originally published in Mahurangi Matters, April 2008
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