One Smart Apple: Using Particle Size Analysis and Rheology to Optimize Cider Production

Cider is an alcoholic beverage produced from the fermented juice of apples. For manufacturing, apples with a high content of tannins are preferred. The apples are first ground to a fine pulp, then pressed to extract the juice. The juice is then fermented, either using the natural yeasts present in the juice or by supplementing it with controlled yeast strains to ensure consistent fermentation. Fermentation consists in two separate steps: first, yeasts convert the sugar to alcohol, then lactic acid bacteria convert the natural malic acid into carbon dioxide. Hence, controlling these two processes enables the manufacturer to modulate both the alcohol content and the sparkling character of the final product. Compared to other alcoholic beverages, cider fermentation takes place at rather low temperatures (4 - 15 °C). This has an important impact on the duration of the fermentation process and hence on the flavor of the final product.

For the usual case where fermentation takes place in tanks, the cider is siphoned off at the end of the fermentation process to remove the dead yeast an the particulate matter, resulting in a clear, sediment-free product. In order to create a more natural-looking product, and also to add back some sweetness and apple taste to the cider, some manufacturers add cloudy apple juice concentrate at the end of the process. In order to give the final product an appealing cloudy appearance while avoiding the risk of sedimentation (which is repealing to the customer), the concentrate needs to be homogenized so that the particles reach a certain size. The mechanical homogenization process aims both at downsizing the particles and at narrowing the particle size distribution, i.e., at giving the particles a more uniform size.

In the present application report, the effect of homogenization on particle size in an apple juice concentrate was investigated using a Litesizer™ 500 particle analyzer. The influence of the concentrated apple juice on the final cider product was also examined. In addition, we sought to establish the rheological properties of the apple juice concentrate before and after homogenization using an Anton Paar rheometer. 

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