I'm looking to concentrate freshly pressed apple juice. In order keep the apple-freshness I would very much like to avoid heating up the juice.
Does anyone have experience with cryoconcentration, is it possible to do yourself?
I was thinking about putting the juice in the freezer while constantly stirring it (using a magnetic stirrer), and once in awhile strain away the ice crystals and hopefully reduce it by half.
Is it possible to do? Any pointers would be highly appreciated.
Best Answer
This worked for me as an experiment in freeze concentration (of plums) and freeze distillation (of a lemon juice/vodka mix). It is not fast.
Remove the pith, stem, seeds, and the rest from the fruit you want to use. If you want to extract with alcohol, add full-strength vodka now, at about 50/50 ratio with the fruit.
Blend it
Freeze in a strong plastic bag, preferably inside a bowl, until it is solid. Twenty four hours should be good but the longer the better to grow the ice crystals
Break it up into a crystalline slurry with a hammer whilst still in the plastic bag (but not in the bowl, of course. This is why the bag needs to be quite robust. Fruit juice does not freeze as hard as water so 'slurrifying' is easier than you would think.
Put the crushed slurry in a sieve, over a bowl and put in the fridge to thaw slowly. Doing it in the fridge is important because you want the whole thing to thaw very slowly and evenly
Leave it until you judge the extract to be about the right strength.
If you are just concentrating fruit juice, it is up to your judgement how long you leave it to 'melt', depending on how strong you want the resulting syrup. A lot of fruits are around 10% sugar so you can get a strong syrup by taking syrup equivalent to about 1/5 of the original (sugar recovery is not complete but I judged it to be pretty efficient because the remaining ice had only slight sweetness).
If you added vodka, it will tell you when it is ready because the melt pauses for a few hours after the alcohol is through but before the water starts to melt. The alcohol will collect all of the flavour chemicals and a lot of the sugars. I did it with lemons (including the zest in the blend). The result was a super-intense liquor.
I do not know what possible value such a labour-intensive method is, but it produces a very clean essence (no heating, you see) and I enjoyed the experiment when my wife was away and could not object. If you try it, please tell me how you get on.