April 7, 2020

Just over a month 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 and the 3-week update on the next blog when I degassed the wine and started the clarification and stabilization processes.

The wine is now into its fifth week. Clarification is complete. The kieselsol–chitosan fining agents did an absolutely great job giving a very clear wine. Check out the picture showing the wine with the added fining agents, then post fining and post filtering.

I gave the fining some extra time than what is suggested in the instructions, but these are unusual times. Given the current Covid-19 pandemic and lock-down, I will not be ready to bottle the wine until I can source some polyaspartate to stabilize the wine against tartrates. (Polyaspartate is a protective colloid that prevents the formation of tartrates.) I chose this route, as opposed to cold-crashing the wine to drop tartrates (more on this below), as the acidity is just where I want it to be at 6.90 g/L (0.69%) for this style of wine. Cold-crashing the wine would drop the acidity and reduce its freshness.

I measured the “clarity” of the wine to gauge fining efficacy — it’s actually called turbidity in winemaking parlance, and is measured in Nephelometric Turbidity Units, or NTU. After 17 days, turbidity measured 0.83 NTU, which, without any filtration, is already below the 1.1 NTU threshold for a wine described as “brilliant” (Ribéreau-Gayon et al. 2012). The fining also “cleaned up” the wine of its oxidized polyphenols, though invisible to the naked eye, to give a beautiful, bright yellow color. This was assessed by spectrophotometric analysis of color, and there was an appreciable decrease in brown-colored pigments. Again! These brown-colored pigments are not visible, but the fining really brought out the brilliant yellow color.

As I wanted to give it that extra sparkle, I filtered the wine with a 1.2 µm (microns) cartridge; this also preps the wine for a final sterile filtration at 0.45 µm at bottling.

The wine tastes wonderful for such a young wine; I’m pleasantly surprised. It exhibits oodles of citrusy flavors and aromas with that subtle hint of petrol I had detected in the last tasting just about two weeks ago. The acidity gives the chilled wine just the right balance and freshness. You’ll recall from my last analysis and blog that it has 2.80 g/L (0.28%) of residual (reducing) sugar. I like the wine so much that I filled a bottle for dinner later this evening; it will pair just perfectly with chicken fajitas.

I will let the wine age in the carboy for now until Mosti Mondiale sends me some polyaspartate. Until I bottle, I will keep an eye on SO₂ levels and make necessary adjustments. Free SO₂ has already fallen to about 75 mg/L (ppm) since the addition of 130 mg/L at the stabilization stage. This drop is in part due to pulling a vacuum in the headspace as the carboy was not completely full. I had taken many samples for testing and, well, tasting.

Back to tartrates and tartrate stability.

I tested the wine’s tartrate stability to see if there would, in fact, be a need for the polyaspartate. I did this using the contact method, which involves seeding a chilled sample with potassium bitartrate (cream of tartar) and monitoring the drop in conductivity using a conductivity probe and meter. If conductivity drops less than 3% until it reaches a steady state, typically in about 30–45 minutes, then the wine is considered tartrate-stable.

Alas! Conductivity dropped by 7% within a minute of seeding and 14% within 5 minutes, and so the wine failed tartrate stability. This means that the wine has an excess of tartaric acid and/or potassium that would cause tartrates to form and drop at colder temperatures, something that definitely be a no-no if it happens in bottles. Some would say that tartrates in bottles is “a sign of good winemaking;” I couldn’t disagree more.

So for now I will continue to let the wine rest in the dark at 13°C/55°F in my cellar until I can stabilize with polyaspartate and bottle it. Aromas and flavors should continue to develop and improve with some aging, so why rush a good thing anyways.

Stay tuned for more updates.

Cheers!

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

REFERENCE

Ribéreau-Gayon, P., Y. Glories, A. Maujean and D. Dubourdieu. 2012. Traité d’œnologie, Tome 2 – Chimie du vin. Stabilisation et traitements. 6e édition. Dunod, Paris.