Cryoconcentrating Cider

I decided to try making ice cider this year. Ice cider is a sweet apple wine made from concentrated apple cider that allows more alcohol production than normal cider, along with residual sweetness after fermentation. Normal cider is about 10% sugar, and this has to be concentrated to at least 30% sugar to make ice cider. The defining feature of ice cider is that it is concentrated by partial freezing, causing ice crystals to form, and the sugars are forced into the remaining unfrozen portion. This can be done either prior to pressing the apples or after pressing the cider, and removing the sugar-rich liquid from the ice crystals resuts in a concentrated cider.

For practicality at home I chose the cryoconcentration technique, which involves freezing already-pressed cider. I started with 10 litres of cider, expecting to get maybe 3 or so after concentration (in the end I got 2.8 L). I used my chest freezer though quickly saw how impractial this is for volume production. Officially ice cider is made by using the cold of winter to do the freezing, and if I had waited a month or two I could have done that, but I wanted to use cider while it was still available in bulk from a local producer (Halls Apple Market).

From a previous experiment freezing a very small amount of cider I had learned that simply freezing it solid doesn't  work, because the sugar-rich portion can't be separated from the ice block. Instead, it has to be turned to slush and the syrup drained from the crystals. I started with half the cider—all that would fit in my freezer at a time—and chilled it until it reached freezing temperature, which took overnight and then some, stirring occasionally so the entire batch would cool evenly and not form a rim of ice around the edge.

As it approached a temperature to start forming ice crystals I started stirring it evey half hour. At one point it reached the supercritical stage, where it was liquid until I stirred and then suddenly turned cloudy with crystals, which was exciting to see. I was anxious to keep small seed crystals evenly distributed so the water would form many small crystals of mostly ice, rather than large aggregates that might trap sugar. Cider slushieI kept the frequent stirring up, each time seeing more of it turn to ice crystals. Ultimately it turned to a cider slushie, a somewhat brown mess of slush in the pot.

At this point I tried to drain the concentrated cider off the ice. I put it in a sieve over a bowl and allowed the liquid to drain off. I stirred the ice to encourage the liquid to flow, but had trouble getting it all off, as I could see by the darker ice that remained in the bottom of the sieve. I risked melting the ice and unconcentrating it if I took too long. I also found (by hydrometer readings) that the concentration of the liquid I drained was not at the target level at first, and had to keep returning to the batch to the freezer to concentrate it further. By the time it was putting off a cider concentrated to the level I wanted, it was so frozen I would have sworn it was fully ice by this point, and it was also quite hard to work with. I set aside the small amount of concentrated cider I had obtained, as well as the much larger batch of ice crystals, which showed upon melting to still have a significant concentration of sugar, meaning I had not effectively separated the sugar as much as I hoped.

The twin problems I had experienced of how much had to be frozen and how difficult it was to separate the concentrate gave me two brainstorms for how to manage the second half of the original batch:

  1. When crystals formed in the mix I didn't have to wait to remove them, but could clear them out in stages, leaving a more liquid and workable mixture behind as the batch continued to freeze;
  2. I needed a centrifuge to force the concentrated liquid off the ice crystals. I ended up putting the ice crystals in a nylon mesh bag (the sort used to filter jellies and the like), and putting that in a salad spinner as my centrifuge.

Clean ice crystalsThese two approaches worked well all in all. As slush formed in the batch, I would scoop the ice crystals into the mesh-lined salad spinner, spin off the liquid, and return the liquid portion to the freezer to keep freezing. When I spun the spinner, initially a lot of liquid would come off and make it hard to spin, so I had to keep stopping, draining the liquid, and then continuing the spin. I did this for several cycles each time I used the spinner, until no more liquid came off and the crystal left behind were nearly white.

I did the cycle of removing liquid from slush and returning the liquid to the batch in the freezer several times as well, until finally the liquid portion was at the target concentration. To regain the sugar I hadn't managed to separate in my first batch I repeated this procedure on the weak portion of that batch. All of this took a week of effort, but in the end worked well. yielding an amount of concentrate about what I anticipated, and an unconcentrated portion with very little sugar in it. The difference between the two was striking—a small amount of dark brown concentrate, and a much larger amount of very pale dilute (though the photo below doesn't show the contrast well, because the larger bowl is deeper than it looks).

Diluted cider on left, and concentrated cider on right

Now that I've been through this I have a pretty good procedure for future efforts:

  • Place cider in freezing location and bring down to the freezing point, stirring occasionally to keep temperature even;
  • When cider begins to form ice crystals, stir every half hour to break them up and disperse them evently;
  • When ice crystals build up to the point it seems more ice than liquid, remove them by straining and using a centrifuge, then return the liquid portion to the freezing location;
  • Continue the process of stirring frequently and removing ice crystals as needed until the liquid portion achieves the desired concentration.

For any reasonable quantity, using the great outdoors rather than a machine to freeze the cider is nearly essential. Even 10 litres of cider took days in my freezer and required a lot of available space. That yielded only 2.8 L of concentrate, only enough for five 500 mL bottles if I'm lucky after losses in the production process. It will require 3 - 4 times as much cider as the desired amount of ice cider, which involves managing a lot of liquid and ice.

Also for future efforts I would really want a proper centrifuge. The salad spinner worked, but barely. The main problem was that it did not have much space below the basket to hold liquid, so I had to keep stopping and draining that liquid to allow more to accumulate. It was also evident that the plastic was not intended for this kind of intensive and prolonged use, and it was hard to reach the speeds I needed as well. I was really wishing for the kind of centrifuge beekeepers use to separate honey from the comb. Anyways, some kind of proper device for spinning liquid from a solid is really needed for this process.