Pre-Fermentation Treatments
Amelioration
Amelioration is simply adding acidulated water to unfermented must with the purpose of reducing the sugar level. Grapes sometimes can have sugar contents that may be high enough to cause stuck or sluggish fermentations. At harvest, grapes may have a Brix greater than 26 and include dehydrated or raisined berries. Degrees Brix is the sugar content of an aqueous solution. One-degree Brix is 1 gram of sucrose in 100 grams of solution and represents the strength of the solution as percentage by mass. During fermentation, the alcohol that is produced can be sufficient to kill the yeast or severely restrict its ability to take up glucose and fructose and hence prevent the fermentation from completing to the desired level.
Calculating Water Dilution
We can calculate the actual volume of acidulated water to add by using Pearsons Square (Rankine, 2004):
Water Quality
When considering adding water to a high sugar must, it's important to think about the type of water available for use and what else might be added to the must along with the water. Mains/potable water is often treated with chlorine, chlorine dioxide, chloramines, ozone and hydrogen peroxide, combinations of these and other minor disinfectants.
Acidulating the Added Water
Tartaric acid, the predominant natural acid in grapes, is recommended for addition although an acid blend with malic and citric acids as well as tartaric may also be used. Bench trials can be conducted to determine the number of grams of tartaric acid required per liter to acidulate the water without affecting titratable acidity of the juice or must.
Risks of Adding Water to Must
Aside from the risk of introducing chlorine-related taints to musts and wines, there are some other risks associated with water additions that should be considered. If the water used to make the addition contains some other kind of taint this could be transferred to the must and the resulting wine. Winemakers should remember that water additions will dilute nutrients and acidity of must. Consequently, it is important to measure the Brix, pH, titratable acidity, YAN and malic acid concentration after the water addition has been made to obtain an initial set of parameters prefermentation. These values can then be used to determine any required additions that need to be made.
Click on the following topics for more information on pre-fermentation treatments.
