First, we describe the characteristics of the fermentation process to produce Icewine and we identify the fermentations problems. Next, we offer a concentration of sugar (40° Brix) for an efficient fermentation. Finally, we focus on the stages of production.
Icewine is produced by fermentation (Saccharomyces cerevisiae) from a frozen grape juice with a high concentration of sugar and acetic acid. Vintners Quality Alliance (1999) established the physical and chemical characteristics of Icewine and characteristics of the winemaking process to produce it. Among the most important are ethanol, glycerol, acetic acid and total acid. The sugar in the juice use for fermentation must have a minimum concentration of 35° Brix (g sugar/100 g solution). In practice, the concentration of sugar is between 32° and 46° Brix (3). High concentration of sugar (a large osmotic pressure) upset the fermentation and modifies the characteristics of wine because it changes the growth and metabolism of yeasts (strain K1-V1116 - 0.5 g / l, Saccharomyces cerevisiae).
Fermentation Icewine presents many challenges for wine yeast. A high concentration of sugar in Icewine juice modifies the metabolism, growth and fermentation. In this condition, the growth and multiplication cellular are reduced and above 52.5° Brix the two processes are stopped and the juice would be theoretically unfermentable. The cellular metabolism of carbohydrates begins to produce glycerol and NAD (P) + and the production of ethanol decreased. To balance NAD (P) +, the yeast cells begin to produce acetic acid, but the limit for this acid into Icewine is 2.1 g/l. So, we must choose a concentration of sugar into Icewine juice to allow optimal growth and fermentation, which generate a wine with composer wanted.
Analyzing information found in the article ''Concentration effect of Riesling Icewine juice on yeast performance and wine acidity'' and other articles we propose to obtain Riesling Icewine by fermentation (K1-V1116) from a juice with a concentrate of 40° Brix. We chose this concentrate (40° Brix) because:
- yeast in the 40° Brix begin to consume sugar almost immediately and continue for 18 days, after which, the fermentation will stop,
- have a good dynamic cellular during the fermentation.
- have a good final report between components analysis (ethanol, acetic acid, etc).
The steps to make Riesling Icewine are: determine chemical composition of Icewine juice, yeast inoculation, fermentation monitoring and determine chemical composition of Icewine.
1) Determine chemical composition of Icewine juice 40°Brix
Riesling Icewine juice composition prior to fermentation (mean value ± SD) should be: titratable acidity (TA) 9.42 ± 0.14 g/l, acetic acid 0.11 ± 0.02 g/l, glycerol 4.85 ± 0.05 g/l, ammonia nitrogen 120 ± 4 mg/l, amino acid nitrogen 484 ± 4 mg/l, glucose + fructose 447 ± 1 g/l and pH 3.15 (2).
2) Yeast inoculation
Wine yeasts are inoculated into Icewine juice (0.5 g/l) using a yeast acclimatization procedure previously described Kontkanen et al. 2004 (1).
3) Fermentation monitoring
Fermentations are carried out at 17°C until the yeast will stop consuming sugar (2).
4) Determine chemical composition of Icewine
Chemical composition of the finished Riesling Icewine (mean ± SD) should be: residual glucose + fructose 235.1 ± 0.05 g/l, titratable acidity 11.8 ± 0.1 g/l, acetic acid 1.79 ± 0.1 g/l, % of TA represented by acetic acid 19%, glycerol 19.95 ± 0.76 g/l and ethanol 94.0 ± 0.9 (11.9% v/v) (2).
More from: Danny
More from: Danny