Blood oranges not only have their own distinct flavor, but they often taste more concentrated than the more familiar orange orange juice. This concentration method takes that aspect and exaggerates it still further. Use this method to concentrate juices to various degrees, depending on your needs.
blood orange juice, strained through a chinois
Put the juice in a 2-quart (2-liter) Erlenmeyer flask (the flask is intentionally large to increase the surface area of the juice and speed its evaporation) with a sidearm.
Place a cork in the top of the flask and, using rubber tubing, hook a vacuum pump to the sidearm (see Vacuum Pumps). Turn on the vacuum. You’ll need to place the flask over low heat because the vacuum and the concurrent evaporation cool the liquid. Simmer the liquid to the consistency and strength you need.