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Goosecross: Pre-harvest Lab Tests

by David on September 13, 2009

In our last post you saw our Owner/Winemaker, Geoff Gorsuch, gathering grape samples from two different vineyards.

Now, back at the ranch, so to speak, he tastes the juice for flavor maturity and also measures the sugar (provides the alcohol), acid (makes wine clean, lively and food friendly; enhances longevity) and pH (kind of like measuring the strength of the acidity – important to the health and stability of the wine). Read more about the significance of these components. Enjoy!

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Sugar: After he juices the fresh grapes, you see him put some of the juice on the lens of a small instrument called a refractometer. This measures the brix or sugar (degrees brix = percentage of sugar). When he holds it up to the light it measures the speed at which light passes through the liquid: The denser the liquid, the slower the light will travel through it, and the higher the reading will be (90% of the soluble solids are sugars). If he harvested the grapes the same day, with the 25 degrees brix reading, the wine would be around 13.5% alcohol.

Acid: Next, you see him titrating to measure the acidity. He’s determining the concentration of the acid in the juice by adding a carefully measured reagent until he sees the appropriate color change.
1. He mixes a pH indicator, with the juice.
2. Then, he adds the titration solution, ½ cc at a time, shaking as he goes, until the solution turns pink. Each cc of solution represents 0.1% total acidity. So, if 6-6/7 cc of solution was used and he knows the total acidity is 6.67%.

pH: The pH meter is really a volt meter that’s been calibrated to measure the pH and the first thing you see is a couple of buffer solutions to help calibrate. Then, he just puts the electrode in the sample and the reading appears on the display (3.22 in this case – fairly tart for a red).

Upshot? He decided to wait. pH  was a little lower than ideal and flavors weren’t quite there.


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