What is tart cherry?

In one line

Tart cherry is a strongly sour cherry from a different species of cherry tree than the sweet cherries people usually eat.

What is tart cherry?
The name on post-workout recovery drinks
You often see 'tart cherry' on post-workout recovery drinks and on supplements said to help sleep. This post explains how tart cherry differs from the cherries we know, what is in it, and what to know when drinking it as juice.
In one line
A strongly sour cherry
A cherry is the fruit of a cherry tree. Tart cherry is a strongly sour cherry that grows on a different species of cherry tree from the sweet cherries we usually eat. That is why it is also called 'sour cherry'.
How it differs from sweet cherry
One eaten fresh, one processed
There are more than a hundred cherry varieties, but they fall into two main groups: sweet cherries and tart cherries. Sweet cherries are mostly eaten fresh. Tart cherries are sour, so almost all are processed, mainly for cooking and baking.
Montmorency
The most widely grown tart cherry
The tart cherry variety grown most in the US is 'Montmorency'. You will often see this name on tart cherry juice and supplements, and most tart cherry studies in people used this variety.
How is it eaten?
Juice, concentrate, powder, capsules
Tart cherry is eaten less as fresh fruit and more as juice, as concentrate made thick by removing water, as dried and ground powder, and as capsules filled with that powder. Studies also used these products.
Where the red comes from
A pigment called 'anthocyanin'
A group of substances that plants make is called 'polyphenols'. The deep red of cherries comes from 'anthocyanins', pigments among the polyphenols. Anthocyanins give flowers and fruit their red, blue and purple colors.
It also has melatonin
A hormone linked to sleep
A 'hormone' is a substance made in one part of the body that travels in the blood to send signals. Melatonin is a hormone the brain makes when it gets dark, setting the timing of sleep. Tart cherries contain melatonin, and so do sweet cherries.
Studies that measured sleep
Fewer than half found better sleep
Pooling the studies that measured whether tart cherry helps sleep, fewer than half found better sleep. In a study where people took tart cherry juice or powder for a month, sleep did not differ between those who took it and those who did not.
Drinking it as juice
About 30 g of sugar per cup
Fresh tart cherries have less sugar than sweet cherries. But tart cherry juice has more sugar than the same weight of fresh fruit. One cup (240 mL) of tart cherry juice has about 30 g of sugar.
Common misconception
Does it have as much melatonin as a pill?
No. To get 2 mg of melatonin, the amount commonly used as a sleep medicine, from Montmorency cherries, you would need to eat about 150 kg of cherries. Tart cherries have far less melatonin than a pill.
Summary
A sour cherry of another species; juice brings sugar too
Tart cherry is a strongly sour cherry from a different species of cherry tree than sweet cherry, and it is mostly eaten as juice or powder. It contains the red pigment anthocyanin and melatonin, but far less melatonin than a pill. Related terms: Montmorency, anthocyanin, melatonin.