Effects of magnesium ions on both VHG batch and continuous fruit wine fermentations

Abstract

In Poland, fruit wines or aromatized fruit wines are semi-sweet or sweet and contain approximately 15-16% (v/v) ethanol. Their production can be classified as a very high-gravity (VHG) fermentation. Magnesium has a beneficial effect on VHG fermentations as it protects the yeast cells against ethanol, osmotic and temperature stress. The effect of the magnesium concentration in an apple must, containing 32% sugars, on the fermentative parameters of batch and continuous fermentations was assessed. In the batch process, a magnesium concentration of ~8.5mg/L resulted in decreased the ethanol production in comparison to a magnesium concentration of ~250, 490 and 970mgMg 2+ /L. The highest amount of Mg also caused a metallic taste. A continuous fermentation was carried out for 2.5months in a four-column packed-bed fermentor. The medium contained ~50, 250 and 490mgMg 2+ /L and the yeast was immobilized on foam glass. During the continuous fermentation, no differences at p≤0.05 in terms of fermentative parameters were seen with magnesium additions. The same beginning amount of magnesium ions in the medium led to a similar use of this element, both in batch and in continuous fermentation. The more Mg 2+ that was present in the medium, the more Mg 2+ was used by the yeast. The results suggest that the minimal dose of magnesium, under the described conditions, is 50mg/L, corresponding to the amount of Mg in the medium prepared using concentrated apple juice and tap water. This finding has industrial significance, as Polish wine companies prepare their fruit musts using tap water.