Ice cider product development : effects of concentration, yeast strains and processing conditions on biochemical and sensory quality traits

Abstract: Ice cider is produced by fermenting apple juice that has been concentrated by freezing (cryoconcentration or cryoextraction). Ice cider is more a sweet wine than a cider, with an intense apple flavour and sweetness, and acidity to balance the flavours. It originates from Canada, where specifications includes a pre-fermentation sugar content of not less than 30 °Brix, and a finished product with a residual sugar content of not less than 130 g/l, containing 7-13 % alcohol. This project aims to investigate and document some of the aspects of ice cider production process for Swedish conditions. The ambition is to start building experience and knowledge useful for ice cider production in Sweden. The scientific documentation on ice cider fermentation and biochemical properties of cryoconcentrated apple juice is very limited. In this project factors important for the quality of cider and ice wine were reviewed, and methods for producing ice cider through cryoconcentration and subsequent fermentation were evaluated. It was demonstrated in this project that concentrating the apple juice by cold has an equally concentrating effect on sugars, total acids and total phenolics. It was also demonstrated that the level of concentration of the juice highly influences the fermentation kinetics and output. Higher sugar level slowed down the rate of fermentation, and the amount of ethanol produced was lower. In order to produce a good ice cider, the juice needs to be sufficiently concentrated to produce the alcohol content and residual sugar level that defines the product, while not be too concentrated and place excessive hyperosmotic stress upon the yeast cells, resulting in slow and potentially stuck fermentations. The juice needs to hold a minimum of 32 °Brix, while a juice of above 42°Brix will be very difficult to ferment. It was further demonstrated in this project that the selection of yeast strain has an effect on level of ethanol produced, and acid development during fermentation of ice cider. The level of phenolics was found to remain fairly stable across different yeast strains during fermentation. The yeast strain was also demonstrated to have a small impact on the flavour of the ice cider.