The must’s high phenol content leads to rapid browning and excessive colour. Gallnut tannins, such as Tannivin® Galléol, work by actively inhibiting the activity of natural oxidation enzymes (laccase, tyrosinase) and help to maintain the typical pale colour of the subsequent wines. When combined with a low dose of Tannivin® Grape, this adds oxidation protection.
The prior enzymation that is required to break down glucan is important. Virtually every ice wine must is heavily contaminated with mucilage, such as glucan, that can make subsequent filtration difficult and even almost impossible. The use of Trenolin® Filtro provides targeted degradation of these retardants and so not only facilitates better preclarification, but also continues working until the resulting wine is filtered lateron. Dispensing with this measure or the use of standard enzymes will cause the ice wine to be unfilterable in nearly every case.
Clean preclarification is also important in sensory terms, in order to remove sensory impurities as fully as possible. The long time on the vine inevitably leads to a certain occurrence of botrytis and other fungi. Purocell® O has proved effective in this case,along with Granucol® GE. The pure yeast cell walls adsorb fermentation-inhibiting ingredients and so assist successful fermentation.
The incredibly viscous juice usually frustrates either sedimentation and flotation. As a rule the only way to achieve preclarification is filtration. As a result, gelatine or pea protein are not absolutely necessary. Once again, LittoFresh® Chito-Flot makes a significant contribution to removal of oxidised phenols and fermentation-inhibiting substances. Theoretically, various filters can be used, but the filter most used in practice is the filter press. Filtration aid VarioFluxx P has become standard for the VarioSan method. For small volumes, monophilic cloth bags combined with TrubEx Neu, a particularly long-fibered cellulose, have proved to be very effective.
Both nutrition and choice of yeast are absolutely decisive for fermentation. Ice wine musts are generally low in nitrogen and thiamine. Both should be supplied in moderate doses with VitaFerm® Ultra. The use of Vitamon® Liquid is ideal during fermentation, adding nitrogen in an easily usable form. Fermentation should take place at 18-20 °C. The high degree of preclarification and enormous amount of sugar impede the fermentation process, which is why the best possible yeast nutrition is all the more important.
Yet even under the best starting conditions, many yeasts which under “normal” conditions are otherwise reliable founder as a result of the large quantities of sugar. Particularly osmosis-tolerant yeast strains are required in order to achieve the necessary degree of fermentation of 5.5% ABV, and even to exceed it if requested. Two yeasts are particularly suitable for assured and organoleptically successful fermentation: Oenoferm® wild&pure and Oenoferm® Klosterneuburg. Simultaneous use of both strains is more or less a well-kept secret. When each is dosed at 15 g/hl, they combine many strengths and the total dosage of 30 g/hl yeast is absolutely necessary for ice
wine. Wild yeast strain torulaspora delbruckii in Oenoferm® wild&pure forms very few fermentation by-products, whilst volatile acids and SO2 are significantly reduced. The highly robust saccharomyces cervisiae Oenoferm® Klosterneuburg starts to ferment very rapidly, achieves a comparatively high degree of final fermentation and can easily be stopped by cold.
Fermentation progress Riesling Eiswein in Rheingau 2021. Fermentation progressed over the length of time shown and was fully stopped at 6.5% ABV. Preclarification with 20ml/hl FastFlow at 1 h reaction time, 100 g/hl Granucol® GE and 50 g/hl Purocell® O. Fermentation with 15 g/hl Oenoferm® Klosterneuburg + 15 g/hl Oenoferm® wild&pure, Vitamon® B, Vitaferm® Ultra, at approx. 20 °C fermentation temperature.
The degree of final fermentation should be determined as much as possible by sensory factors – too little alcohol makes ice wine seem flabby and stolid, too little residual sugar over-emphasises the high level of acidity expected in this vintage. If the desired balance is achieved, fermentation can easily be stopped by cold and filtration.
The addition of sulphur should be high but adjusted to the marketing launch. A dosage of 120 mg/l SO2 and a possible second addition to adjust the free SO2 a couple of days later would be typical. The high residual sugar buffers against the released SO2, so that even seemingly low quantities of 20-25 mg/l SO2 provide adequate protection. These values must be stable, however, and be checked by multiple measurements over one or two weeks.