POTASSIUM BICARBONATE (KHCO3)
Fall Bright, The Winemakers Shoppe
NOTE: Acid reduction with Calcium Carbonate, Potassium Bicarbonate, or Acidex can not exceed more than a .4% total reduction either by combined or any one application.
Addition of 3.4 grams/gallon will reduce acidity by 0.1% with a maximum reduction of Total Acid (TA) of 0.25 to 0.3%
Potassium bicarbonate reduces the acid level of wine by neutralization
and precipitation. It neutralizes acid by converting one to the hydrogen ions of tartaric acid to water and then combining with the remaining tartrate
ion to form relatively insoluble potassium bitartrate (KHT).
· The use of potassium bicarbonate does not add anything foreign to wine. All that occurs is an increase in K+ concentration and a decrease in both acid and tartrate.
·
The procedure for using potassium bicarbonate is also simple. It is added in a single dose to the entire batch of wine, rather
than in serial addition recommended for calcium carbonate and Acidex. Addition of 3.4 grams/gallon will reduce acidity by 0.1% with a maximum
reduction of Total Acid (TA) of 0.25 to 0.3%
Because it neutralizes the acid, potassium bicarbonate raises the pH of the wine more than calcium carbonate. This
can be an advantage in dealing with problem varieties with a pH below 3.0 and a TA above 1.0. Raising the pH of such wines will help soften their
acid taste. However, this can also be a major disadvantage or limitation in its use. It is
recommended only for use with wines with a pH below 3.0 and a T.A. above 1.0
to insure that the final pH will not exceed 3.6. Maximum reduction of TA is in the .25 to .3% range.
Precipitation of the potassium bitartrate resulting from the use of
potassium bicarbonate is brought about by cold stabilization. It is important for the amateur
winemaker to make use of potassium bicarbonate while cold weather is still available.
The cold stabilization accounts for about 25% to
50% of the calculated acid reduction.
Seeding with potassium bitartrate enhances the precipitation of tartrates during cold
stabilization. The
wine is chilled to a temperature of 26oF and very finely ground potassium bitartrate crystals (cream of tartar) are sprinkled on the surface. In this basic procedure, about 2-3 grams of potassium bitartrate are added per gallon and 2-3 weeks allowed for the precipitation to run its course.
Dropping through the wine, they grow as they attract more potassium bitartrate out of solution.
Super seeding is the use of a mega dose of 4 grams/liter and keeping the wine in agitation for 2-3 hours at 26oF. Without seeding, the cold stabilization (detartration) should be extended for a month or more rather than weeks. (Crystals from earlier reactions can be ground up with a mortar and pestle and recycled for seeding.)
References: Eastern Grape Grower and Winery News, August/September 1983, AWS Manual #14: Wine Acidity: Taste, Measurement, Control, Drs. R. Plane and L. Mattick