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| A Brix reading of 15 by refractometer |
I took Brix readings of the Rondo grapes this afternoon and the results are not encouraging. The first reading was just 15° Brix (SG 1.060) and the second was 19.2° (SG 1.080).
The Brix measurement of a liquid fluctuates according to temperature. The Brix of a cold sample will measure higher than the same sample at room temperature. Therefore, our Brix is likely lower than my readings taken at 13.9C degrees as the device is calibrated to 20C.
The highest temperature yesterday was 15.7C and today it's not made it past 14.2C with a northerly breeze. The temperature dropped to 12.1C overnight. With the days getting shorter, no sunshine and cold temps, it's not looking like we'll get into the 20s. We'll have to harvest and fortify with sugar. Not sure how to do those calculations so I've a new thing to learn again this year.
Brix can be expressed as a percentage of sugar in the liquid. For instance, if a juice measures 20° Brix, that means the juice is 20% fermentable sugar. Although defined specifically as percent sugar (sucrose), all dissolved solids in the juice affect the Brix measurement.
How much sugar should you add to grape juice that already has 15 grams sugar per 100 ml, to ferment to make wine? When sugar ferments, roughly half becomes alcohol and the other half becomes carbon dioxide. So your 15g of sugar will make approximately 7.5 g of alcohol in 100 g (100 ml) of wine, giving a wine of around 7.5% alcohol. If you want to make a wine with 12% alcohol, you will need another 9 g of sugar per 100ml. You can get technical with molecular weights and so on or you can get a hydrometer and just add enough sugar to get a sensible starting gravity.
The Pinot Noir grapes are tiny hard balls not even close to veraison, so I think that's a fail for this year. Who knows what next year will bring. At least the Solaris is bubbling away, which is very encouraging for the fermentation. My yeast was still good.
Even the cat doesn't want to be outside today.
