Key Lime Juice

One US cup of Key lime juice weighs 246 grams (8.7 ounces). Going the other way, 100 grams is about 0.41 cups.

Also called bottled Key lime juice, Key West lime juice, Mexican lime juice, West Indian lime juice, fresh Key lime juice.

Citrus juices compared: cup weights side by side, the source behind each, and why they differ.

A cup of Key lime juice weighs 246 g (8.7 oz), a density of 1.040 g/mL. USDA weighs a cup of bottled lime juice at 246 g and fresh lime juice at 242 g, and Health Canada's tablespoon of bottled lime juice agrees. King Arthur's 227 g would make the juice lighter than water and is rejected.

Key limes (Citrus aurantifolia), also called Mexican or West Indian limes, are small, round, thin-skinned and seedy, and they ripen to yellow. The common supermarket lime is the larger Persian or Tahiti lime (Citrus latifolia). Key lime juice is the base of Key lime pie, where it sets sweetened condensed milk without baking much. Most of it is sold bottled: Nellie & Joe's Famous Key West Lime Juice, the best-known brand, is filtered water and Key lime juice from concentrate, brought back to normal strength.

USDA has no record for Key lime juice as such. Its SR Legacy record for bottled, unsweetened lime juice (FDC 168157) gives 1 cup = 246 g and 1 fl oz = 30.8 g, and its fresh lime juice record (FDC 168156) gives 1 cup = 242 g. Health Canada's Nutrient Value of Some Common Foods weighs 15 mL of bottled lime juice at 16 g, against 15 g for bottled lemon juice; whole grams on a tablespoon are a coarse measure, but the reading is consistent with the other two. Nellie & Joe's label gives a 1 teaspoon (5 mL) serving and no gram weight.

The physical check: a juice's density follows what is dissolved in it. A study of Mexican limes measured their juice at 9.0 to 10.3 °Brix through the harvest season, with 5.4 to 7.5% acidity as citric acid. A liquid carrying about 10% dissolved solids weighs about 1.04 g per millilitre, 246 g per cup, exactly USDA's bottled figure. Persian lime juice measures a little lower in published studies, about 7.3 to 9.6 °Brix, which fits USDA's 242 g for fresh lime juice. The two limes differ in aroma and acid balance far more than in weight.

King Arthur lists Key lime juice at 1 cup = 8 oz = 227 g, 0.960 g per millilitre, lighter than water. An acid juice cannot be lighter than water. A cup is 8 fluid ounces, and 227 g is 8 weight ounces: the fluid ounce has been read as a weight ounce, the same mistake as King Arthur's 227 g cup of water and its 14 g tablespoon of lemon juice, and this entry rejects it.

The fruit decides how much juice you get, not the weight of the juice. USDA counts the juice of one Persian lime at 44 g, about five or six limes per cup; Key limes are a fraction of the size, so a cup takes several times as many.

Practical guidance: use 246 g per cup of Key lime juice, 123 g per half cup, the usual amount in a Key lime pie, and about 15.4 g per tablespoon. A 16 fl oz bottle holds 2 cups, about 490 g. Bottled and fresh juice weigh the same within 2%, so a recipe written for one works with the other by weight or by volume; the difference is flavour.

The following published figures for Key lime juice are rejected here, with the physics or standards reasoning behind each rejection on its own page:

• King Arthur Baking Ingredient Weight Chart: 227 g per cup