There are two ways to make juice concentrate from fruit. They depend on the type of fruit you are using.
For wetter, easily juice-able fruits, go to Step 1: Frozen Concentrate. Good for oranges, lemons, many other fruits if you have a juicer.
For fruits that will be a pain to juice, go to Step 2: Boiled Concentrate. Good for berries, pomegranate, apples, pears, etc.
Step 1: Frozen Concentrate
The method of freezing is based on the fact that juice can be extracted from ice- if you've ever made a fruit juice popsicle and sucked on it too hard, you remember that you sucked all the flavor out and had a pure ice-sicle left on the stick! Here's how to use that.
- Juice your fruit by any method- a hand juicer, a lime squeezer, by hand, into a freezer-safe container.
- Freeze it. This might take a while.
- Set up a container that can hold all of the juice with a narrow funnel on top. Upend frozen juice on top of it.
- Let sit at room temperature while the juice drips out.
- When the ice is sufficiently clear/white, you're done! Throw out the ice and keep the concentrated juice.
- Repeat freezing/thawing as necessary.
I juiced about 17 oz. of orange juice, and by repeating the freezing/thawing method described above twice, condensed to about 10 oz. It's much stronger tasting and thicker in consistency. You can also see a darkening of the color (the photos are in order).