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Lemon Juice (To preserve lemon juice)
To preserve lemon juice for future use it may be boiled down to half its bulk. This will keep indefinitely.
A single line with a lot left unsaid. The technique works, but the reduction needs care and the keeping claim does not survive contact with a modern understanding of spoilage.
- The hinge: keep it below a rolling boilHard boiling drives off the volatile oils that make lemon juice taste of lemon and leaves a flat, faintly cooked sourness. Reduce at a bare simmer, uncovered, until the volume has halved; the citric acid concentrates regardless of how vigorously you boil.
- Use a non-reactive panLemon juice at this concentration will pull metal out of aluminium, unlined copper or chipped enamel and taste of it. Stainless steel or glass only.
- Strain firstPips and pith left in the pan release bitter compounds over a long simmer. Strain through a fine sieve before reducing, not after.
- "Keep indefinitely" is not trueThe acidity is high enough that botulism is not a concern, but molds and acid-tolerant yeasts grow happily on an unsweetened acid concentrate left in an open cupboard. Refrigerate the cooled concentrate, or freeze it in ice-cube trays, where it genuinely does last for months.
- ReconstitutingHalf-bulk concentrate is roughly twice-strength juice: one part concentrate to one part water gives you something close to fresh, though flatter in aroma. Judge by taste rather than arithmetic, since lemons vary in acidity by variety and season.
- YieldSix to eight medium lemons give about a cup of juice, so half a cup of concentrate. It is worth doing in quantity, since the losses are proportionally worse in a small pan.
- Where it belongsThis is a bar and soda-fountain ingredient, not a cooking one. Fresh juice is better anywhere it is not going to be masked; the concentrate earns its place in lemonade syrup, punch and anything sweetened heavily enough to cover the loss of top notes.
Uncle Sam's Water Wagon belongs to the temperance-era literature of the soft drink "" the title plays on the phrase "on the water wagon," slang for having sworn off liquor " and its Syrups section is essentially a soda-fountain manual. A fountain in a small town could not count on good lemons year-round, so a boiled-down juice held in the back room solved an obvious problem, the same logic that produced bottled lemon squash and lime cordial. The technique itself is far older than the fountain: boiled-down fruit juice under the name "rob" long predates the soda counter, and its best-known application was the eighteenth-century navy provisioning trade, where "rob" of lemon or orange " a thickened, boiled-down juice " was carried against scurvy, though the boiling was later understood to destroy much of the vitamin C the sailors were counting on. What survives here is the sugar-free version, useful precisely because the fountain man would add his own syrup at the counter.