How should you process your apples to make juice? Do you mill and then press them? Do you even need to press them? A. Censures and associates researched an interesting alternative for juice extraction: microwaves(1). Their research focused on plums, apricots, and grapes, which tend to be softer than apples but the concept could be viable. For me, this process is very interesting for many adjunct fruits as well as some crab apples. They explored using unfrozen and frozen fruit. Their goal was to assess not only yield but also juice quality. They measured quality by the color and compounds found in the juice. They discovered that the microwave process inactivated some enzymes like polyphenol oxidase, which causes enzymatic browning. As a result, the juices were brighter colored. Judging panels also noted higher acidity and viscosity of the juice. In general, the juice was deemed to be a higher quality.
Their method involved a household microwave so this wasn’t something that could only be replicated on an industrial scale. When evaluating both frozen and unfrozen fruit, they found the frozen fruit improve the yield, which makes sense as freezing in home freezers bursts the fruit cell walls and aids in extraction. They also assessed the different power to weight ratios to determine the optimal ratio. They found that the best extraction ratio was the lowest power to weight ratio (0.5 W/g). However, this took the longest time. They hypothesize that while the higher power densities reduced the time and increased the extraction rate, some of the juice was lost to evaporation, which decreased the yield.
I have some frozen blueberries that I am planning to use for an adjunct this year and I plan to test this method with these. I believe blueberries should be comparable to grapes and I plan to utilize a 1.0 W/g ratio in my trial. The one modification that they utilized was that they allowed the juice to flow out of the microwave as it was extracted, thus reducing how much the juice was heated in the process. I don’t plan to drill a hole in my microwave so I will modify the setup slightly. However, other research I have been reading indicates that microwaves can also be used to inactivate yeast and micro flora without degrading the juice or cider quality. This is because the temperature change is almost instantaneous. As always, I thought this was some interesting research that was worth sharing. Remember to experiment but experiment safely as microwaves can generate a lot of heat and potentially create pressure inside some fruits. I also have some other ideas for using microwaves so look for new articles on the topic.
(1) A. Cendres & associates, An innovative process for extraction of fruit juice using microwave heating, LWT – Food Science and Technology 44, 2011
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