Prune juice

One US cup of prune juice weighs 256 grams (9 ounces). Going the other way, 100 grams is about 0.39 cups.

Also called 100% prune juice, dried plum juice, prune juice with pulp.

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

A cup of prune juice weighs 256 g (9 oz), a density of 1.08 g/mL, the heaviest of the common fruit juices. USDA weighs a cup at 256 g and Health Canada's 125 mL at 135 g, 255.5 g per cup, within 0.2%.

Prune juice is not pressed like other juices, because a dried plum has too little water to press. It is made by soaking or cooking prunes in hot water and extracting the dissolved fruit, then filtering it, or leaving fine pulp in for the versions sold as prune juice with pulp. The result is dark, thick and very sweet: USDA lists 81.2% water and 16.4 g of sugars per 100 g, plus sorbitol, the sugar alcohol that gives prune juice its laxative reputation.

USDA's Standard Reference record for canned prune juice (FDC 167753) gives 1 cup as 256 g and 1 fl oz as 32.0 g, both 1.082 g/mL. Health Canada's Nutrient Value of Some Common Foods weighs 125 mL of ready-to-drink prune juice at 135 g, 1.080 g/mL. Two independent government measurements agree, so the entry is held at high confidence.

The physical check: the FDA sets the minimum strength of 100% prune juice at 18.5 °Brix, the same 18.5% dissolved solids that USDA's own purchase specification requires, and a sugar solution of that strength weighs 1.073 g/mL by the USDA sucrose table, 254 g per cup. Prune juice measures a little heavier, 1.08 g/mL, because its suspended fruit solids and sorbitol add weight that a refractometer reading does not fully count.

Among juices on this site it sits above grape juice (253 g per cup), pineapple juice (250 g) and apple juice (248 g), in the order of their dissolved sugar. One database transcription lists a cup of Sunsweet prune juice with pulp as 8 fl oz = 226 g, which is 8 weight ounces read as 8 fluid ounces and would make it lighter than water; it is not Sunsweet's label and is not used.

As with any juice, the way the cup is filled does not change the weight, since a liquid leaves no air in the cup. What does change it is the pulp: prune juice with pulp carries more suspended fruit solids, and USDA's and Health Canada's figures both describe ordinary filtered prune juice. A cup with pulp may weigh a few grams more, within the tolerance this site allows for liquids.

Practical guidance: use 256 g per cup, 128 g per half cup, 64 g per quarter cup and 16 g per tablespoon. A 32 fl oz bottle holds 4 cups, about 1.02 kg. In baking, where prune juice replaces some of the fat or liquid, weigh it if the recipe gives grams; a liquid measuring cup is otherwise accurate enough.