Just as in red wines, tank geometry is also important in white wine production. In the production of red wines one wants a balance of diameter to height ratio that allows the thinnest possible cap while balancing that with real estate needed for the tanks footprint. The norm is a 1.5:1 to 1:2 (diameter to height) ratios.

In white wine production cap management is replaced with thermo management issues. In order to produce fruity aromatic wines such as Riesling, Sauvignon Blanc, and others one need to be able to tightly control the fermentation temperature to allow a slow fermentation to keep aromatic compounds in solution.

To do this many winemakers employ the use of jacketed tanks with a 1:2 to 1:5 ratios. This is to insure a large chilled surface to volume ratio. Tanks over 1:3 ratios, depending on volume require seismic bracing, on site fabrication, high ceilings, if indoors and last but not least large cooling jackets.

Another issue that is seldom mentioned is as the diameter to height ratio gets larger the lees bed gets thicker. This can be a real problem on long fermentations where the dead yeast cells become compacted and start to breakdown. One way to resolve the lees problem is to stir the lees bed with an agitator. This also lends to more complex wines and better mouth feel. Again the problem is that with a tall narrow tank it is almost impossible to efficiently distribute all the lees.

The Solution:

Oval tanks have been long used in Europe, especially in Germany for the production of white wines. They take up less room then a comparable size cylindrical tank; have larger bottom surfaces for a thinner lees bed. The semi circular bottom of the oval tank allows efficient and complete agitation of the lees throughout the fermenting juice. The narrow width of the oval tank promotes very efficient cooling equivalent to typical cylindrical tank having five times the cooling surface. This is a big savings in cooling loss due to less active surface area.

Comparison:

Let’s compare a typical 2000 liter Oval tank to a standard cylindrical tank with the same volume;

As you can see from the above table that for the same volume of wine:
• The oval tank has about 6 times the bottom surface area of the cylindrical tank allowing the lees bed to be 1/6 the thickness of the cylindrical tank
• Uses about 2.5 times less cooling surface for the same volume, a great energy savings.
• Saves precious floor space
• Fruit forward wines
• Easy to control wines sweetness due to fast and efficient cooling.

Picture of a row of 3000 Liter Oval Tanks

The tanks on the left are four of nine tanks purchased by Left Foot Charley Winery in Traverse City, MI for the production of Rieslings Pinot Grigio and other white wines.

More on diameter to height ratios:

This past season I studied what effects if any tank geometry had on the finished wines characteristics. The study involved a small lot (400 Liters) of Viognier at Les Chenes Estate Winery Livermore, CA. The grapes where “whole cluster” pressed and the juice was allowed to settle in a refrigerated tank for 48 hours at 5° Celsius to allow the gross lees to settle out. The juice was racked into a 400 liter tank and allowed to warm up to 12° Celsius before inoculating with D21. Once the fermentation was started the juice was agitated and pumped into two 200 liter tanks, one having a (D:H) ratio of 1:2 the other 1:3. Both tanks were set to a temperature of 10° Celsius and fermented for 22 days to dryness. The wine in both tanks were racked off the sediment and cold stabilized.

The Results:

During the fermentation the fermenting juice in both tanks had the same vinous flavor and aroma profiles, green tea and apple. The surprise came after the wines where cold stabilized. The wine fermented in the tank with the 1:3 ratio kept the vinous quality and the wine fermented in the tank with the 1:2 ratio a bouquet of pears, pineapple, apple, canned peach let’s just say a fruit cocktail.

In closing, tank geometry has to be considered when wine style is important.

Dwight J. Busalacchi
Mio Vigneto Products, Inc
Importer of custom stainless steel winery equipment
www.miovigneto.com