Cool Fermentation Techniques: Maximizing aroma retention in white wines
This article by Daniel Pambianchi is from WineMaker Magazine, April-May 2007. (NOTE: You can get a free trial issue of this magazine. Go to the website. ) Pambianchi is General Manager of Maleta Estate Winery (Niagara) and author of Techniques in Home Winemaking: A Practical Guide to Making Chateau-Style Wines , rev. ed, Montreal: Vehicule Press, 2002 (available from Amazon.ca for $16.12). The article has been edited somewhat with additional comments by Peter Huyghebaert, the Club member who submitted this article to Pressing News.
Cool fermentation in white winemaking has a number of benefits that are important in making fruit-forward wines.
Most important, the cooler fermentation, usually carried out in the 13-18C range, significantly slows down fermentation and allows slow aromatic development enabled by a yeast strain specifically chosen to enhance aromas. The temperature must be maintained above the yeast’s minimum fermentation requirement to avoid a stuck fermentation. Depending on environmental factors such as temperature and Brix, fermentation can take several weeks.
As great effort goes into aromatic development, the cooler fermentation preserves the subtle flavors and aromas by minimizing the loss of precious flavor and aromatic compounds that could easily be volatized with an otherwise vigorous, high temperature, fermentation.
Important side benefits of a cool fermentation include reduced risk of microbial spoilage and oxidation owing to the lower temperature.
Most white varietals will benefit from cool fermentation. Examples of wines and styles include unoaked Chardonnay, Sauvignon Blanc, Pinot Gris, Gewurztraminer and Riesling.
Home winemakers can replicate with relative ease the cool fermentation techniques used in commercial wineries.
As soon as the juice is pressed, add sulfite at a rate of up to 35ppm depending on the quality of the fruit or juice. If the grapes show a lot of rot and/or damage, use the maximum rate. Most whites to undergo cool fermentation where refreshing acidity and full flavors and aromas are desired will not benefit from malolactic fermentation.
Allow the juice to settle for 24 hours and then rack to another carboy or tank in preparation for fermentation. Be sure to maintain a cool environment (below 13C if possible) - during the settling period to avoid a spontaneous fermentation from wild yeasts.
Assuming that you do not have the luxury of temperature-controlled, stainless steel tanks and are instead working with carboys or similar glass containers, you will need one or more large containers that can accommodate carboys in width and height. You will be immersing containers in a chilled-water bath. A large plastic vat works well for this purpose. Chose the appropriate yeast strain for cool fermentation and determine its temperature range. Your desired cool fermentation temperature will need to be slightly higher than the yeast’s minimum temperature tolerance.
PH: An old fridge that can accommodate a carboy or two can work well as your fermentation environment. There are different yeast strains which can work well cool. Chose among them for the specifics of aroma development in the varietal you are fermenting. D47, VIN13, VL1 and VL3 are possibilities. See “Yeasts commonly used by NW members for white wines on our web site.
Rack the juice from the sediment and transfer to a clean, sanitized carboy. To reduce the risk of a stuck fermentation, use GOFERM in rehydrating your yeast. Have the juice at a slightly warmer temperature than the desired cool fermentation and add the yeast/nutrient solution. Secure the carboy with a fermentation lock and let stand. Fermentation should start within 24 hours.
In the meantime, as close as possible to the onset of fermentation, prepare the setup for cool fermentation by pouring sufficient cold water into the vat so that the carboy will be completely immersed to right above the shoulder. The water temperature should be at your desired cool fermentation temperature. Use a large floating thermometer and leave it in the water. Add ice to the water if you need to lower the temperature. Make sure you have a good supply of ice throughout the cool fermentation period to keep the temperature steady. Keep the ambient temperature as cool as possible to reduce the need to cool the water.
PH: I would put the empty carboy into the vat, then rack the juice into it, then the yeast, wait for fermentation to get going fairly well, then add the cold water. Freezing water in plastic milk jugs and adding them to the vat is a simpler way—recycling them two or three times a day keeps the fermentation quite cool, especially if you have your setup outside, in the coolest place possible, such as under a deck or on the North side.
As soon as fermentation starts transfer the carboy to the chilled water vat making sure that the carboy is immersed to the shoulder. Maintain the water at the desired temperature by adding ice as required. As fermentation progresses, temperature will rise and you may need to replenish ice at shorter intervals.
PH: A yeast nutrient such as Fermaid K should be added depending on the nutrient requirements of your yeast - see our web site on “making white wines“ and our yeast listing with nutrient requirements. In general, for a 23l carboy add 4-6 grams the first week and 2-3 more when the fermentation is half way through.
Monitor fermentation progress twice daily by taking hydrometer and temperature readings, and stir the sediment. Do not let temperature fall lower than the desired temperature.
PH: I have not found this so critical, a number of times my carboys have sat outside in January at -10C and the fermentation kept chugging along, albeit quite slowly (this was with Vin13, VL1 and VL2); stirring was not done at all.
Fermentation will be slow and steady, and can last for several weeks. It is complete when the specific gravity is steady at 0.995 or less. For a light-bodied white wine, rack the wine from its lees as soon as fermentation is complete. For a fuller-bodied style wine, you can leave the wine on its lees for another couple of weeks while stirring the lees once or twice daily. Be sure to keep the container topped up during this time.
PH: To ensure fermentation does not stick, it pays to warm the wine up to 18-20C towards the end—hitting it with 15ppm SO2 could also help (as per Ray Bodnar’s advice).
Age the wine in glass or stainless steel tanks for at least 6 months, then fine and/or filter as desired, stabilize the wine, adjust the free SO2 to 35-45ppm and bottle. And Voila! Cool fermentation at home. You can start enjoying the fruit of your labor shortly after bottling.