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I used to make no-bake pies as a kid that consisted of whipped topping, condensed sweetened milk, and frozen lemon- or lime-aid concentrate (thawed) mixed together and poured into a graham cracker pie crust then chilled to set.

The recipe I learned called for a small can of frozen concentrate, a can of sweetened condensed milk, a 12-16 ounce container of whipped topping and a 9 inch pie crust. But lately all I can find are large cans that result in a runny pie filling that doesnt set well.

I would like to try with homemade lime or lemon concentrate but how would I go about concentrating the juice?

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2 Answers 2

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Some fruit juices can be heated to drive off excess water (especially those with a higher sugar content) but citrus doesn't tolerate this well. Fresh-squeezed citrus will get bitter and acrid if reduced.

Instead, squeeze your citrus as normal and freeze the juice in an open container. Once it's set into a solid block, place it into a funnel or strainer over a collection vessel. The juice itself will run off more quickly and collect in the vessel, while the ice crystals stay in the strainer (until they melt, at least - don't let them melt all the way, or you're back to the beginning). Once the ice looks very lightly colored, discard it and enjoy your concentrated juice. You can repeat this process if you want further concentration, though eventually there will come a point where the juice is so concentrated that it won't freeze at conventional freezer temperatures.

Good instructions for this process here - it's really quite simple!

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I suspected some form of freeze-distilling would work, thank you! –  David Wilkins Aug 15 at 12:01
    
Very interesting information. I have never reduced lemon juice, and wrote my answer assuming that it will work similarly to the other juices I have reduced. I wonder why cooking orange marmalade doesn't produce the acrid taste you describe. –  rumtscho Aug 15 at 14:39
    
@rumtscho I think it does, a bit, but the additional sugar in orange juice suppresses the flavor. Lemons and limes have less sugar and so the bitterness stands out more. I think there's also some action from enzymatic action and oxidation, but I don't know for sure - I'm basing this entirely on observation. –  logophobe Aug 15 at 15:10

All you need to do for a good concentrate is the treacle route. You heat your juice to somewhere above 60 Celsius (below is generally dangerous, although lemon juice is probably acidic enough to not worry, and besides will go too slowly) and 85 Celsius, and keep the temperature stable until you have reached the consistency you wanted. If you see a simmer, reduce the temperature.

Lower temperatures will give you better taste, higher temperatures will give you longer running times. Making a concentrate takes many hours.

Both lemons and limes will need a much longer time than traditional treacle, because they don't have the high fructose content found in other fruits. Seeing that you're making a cake, it is probably best to also add sugar at the beginning, 10-15 g of sugar per 100 ml of juice should be a good starting point.

Choose a wide mouthed pot for the concentrate in order to get more even temperatures within the pot (as opposed to a hot bottom and cool surface) and to speed up evaporation. Using a frying pan can be a good option. Don't cover the pan/pot.

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