March 20, 2020

Just less than three weeks ago I started a batch of Finger Lakes Riesling from a Limited Edition Meglioli Riesling kit with 100% grape must. You can read about the kit and the initial winemaking in my first blog.

With fermentation now complete and the lees having settled for the most part, I am now into Day 17 and the wine is ready for degassing, clearing and stabilizing.

Before proceeding with those operations, I measured some key parameters to see how the wine has changed and evolved during fermentation. The following table compares the relevant initial measurements with today’s.

The wine has fermented dry leaving some 2.80 g/L (0.28%) of residual (reducing) sugars, having converted sugars into approximately 12.3% ethanol, or at a rate of 0.578 the initial Brix. A factor of 0.57 is often used to estimate the expected amount of alcohol, or potential alcohol (PA) to be produced by yeast.

Total acidity (TA) has increased from 5.14 g/L to 6.90 g/L with a pH drop from 3.42 to 3.31. During fermentation, a drop in tartaric acid with a corresponding drop in TA is expected as potassium bitartrate (KHT) formed becomes less soluble as ethanol concentration increases. Since TA increased, the juice likely had a higher percentage of malic acid with little tartaric acid available to interact with potassium ions and drop out as KHT, which could be expected with juice sourced from a cool-climate area like the Finger Lakes. The increase in TA would then be attributed to new acids formed during fermentation, succinic acid being the most significant.

I like the balance in taste here, so I will not want to drop the acidity further by cold stabilization, electing instead the use of a protective colloid, like a polyaspartate salt or a solution of carboxymethyl cellulose (CMC), to prevent KHT crystals from forming.

More on TA from a taste perspective in the Tasting Notes section below.

All other parameters show normal results.

Color parameters are monitored to assess color evolution and to identify any potential issues during aging. A₄₂₀ is the absorbance (in absorbance units, or a.u.) measured at a wavelength of 420 nm; it is a measure of the yellow component of the color. A₄₄₀ and A₅₂₀ are absorbances measured at 440 nm and 520 nm, respectively; these are “browning” indicators and will help evaluate aging and detect oxidation issues. I am looking at aging the wine for years, and so, these parameters will help me make a good assessment.

TASTING NOTES

The wine definitely tastes very dry, but quite refreshing with its zesty acidity. There are attractive sweet-fruit notes with pleasant citrusy aromas on the nose and flavors on the palate. There is just a hint of petrol too; I expect this to jump to the forefront as the wine ages – it is a cool-climate Riesling after all.

DEGASSING, CLEARING AND STABILIZING

I racked the wine into a pail and then degassed for about 3 minutes, as per instructions, using a stir paddle mounted on an electric drill. Since I am often asked if there are any risk in whipping the wine and introducing excessive amounts of oxygen, I measured the amount of dissolved oxygen (DO) in the just-racked wine and monitored the uptake during degassing. The initial DO was 0.65 mg/L and rose to 1.22 mg/L by the end of degassing – so DO essentially doubled in about 3 minutes. This is still relatively small as I often see higher levels just from simple racking operations and much higher levels from filtration, for example. Kits also come with high amounts of sulfite to be added, so that will take care of even abnormally high amounts of oxygen, a not-uncommon occurrence with beginners.

I added the 5-g packet of potassium metabisulfite; this corresponds to about 125 mg/L (ppm) of free SO₂, and so, the wine will be well protected until bottling and during bottle aging. I will measure free SO₂ prior to bottling to get a sense of how much SO₂ is consumed and lost between now and bottling.

Then I added the pack of kieselsol, stirred the wine, then added the pack of chitosan for clarifying the wine. I know these work quickly and effectively, and so I should have a very clear wine within a week or two.

And lastly, I added the 5-g packet of potassium sorbate, which adds about 160 mg/L of sorbic acid, a preservative used to inhibit renewed yeast fermentation. It’s a bit high for a 12% ABV wine, but, with kits, you can never be too careful. I added the packet although I have only 2.80 g/L of residual sugars and that I also intend to sterile filter and bottle under vacuum.

The wine will now rest in the dark at 13°C/55°F in my cellar until the next processing step.

Since 23-L (5-gal) carboys are actually slightly bigger, and given the losses from racking and taking samples for lab analysis, my 23 liters of wine is down to some 22 liters. I prefer to not top up the carboy, not even with a similar wine, because I want to assess a totally unadulterated wine, however small the top-up addition might be. Instead I will use a Headspace Eliminator from the maker of the All in One Wine Pump to extract headspace oxygen and protect the wine.

I’ll be back when the wine has cleared and is ready to be bottled.

Cheers!

P.S. You can also follow my winemaking in my Home Winemaking group on Facebook.