Sour fruits ranked by acid: the 12 most sour fruits, with a number each

Sour fruits are sour for one measurable reason: acid, and how much of it the fruit carries per gram. Food scientists put a number on that two ways. Titratable acidity is the share of the fruit's weight that is acid, written as a percentage. pH is how strongly that acid behaves, on a scale where lower means sharper. Put both numbers beside a dozen fruits and the ranking of the most sour fruit is not the one most people would guess. Lemon is not first.

How the ranking works

The list below runs from the most acid to the least, by titratable acidity, with the pH beside it. The pH figures are the ranges in the FDA's table of approximate pH values for foods; the acid percentages are the ranges that food-science references and university extension tables commonly cite for ripe fruit. Ripeness moves every number, so each one is a range, and a fruit at the top of its range will taste closer to the fruit above it on the list.

One thing the numbers do not show on their own is which acid. Citric acid, the lemon acid, hits fast and fades fast. Malic acid, the green-apple acid, arrives a beat later and stays. Tartaric acid, the grape and tamarind acid, sits between the two with a drier finish. Two tart fruits can share a pH and taste nothing alike because of that.

The 12 most sour fruits, ranked by acid

1. Tamarind. Titratable acidity 8 to 18 percent, nearly all of it tartaric. pH about 2.5 to 3.3. The sourest fruit on any list, by a wide margin. The pulp is a paste rather than a juice, which is why one spoon of it seasons a whole pot.
2. Lemon. About 5 percent citric acid by weight: a 2008 analysis in the Journal of Endourology measured lemon juice at roughly 48 grams of citric acid per liter. pH 2.0 to 2.6. The standard every other sour fruit is measured against.
3. Lime. About 4.5 percent citric acid, around 46 grams per liter of juice in the same study. pH 2.0 to 2.8. Nearly a tie with lemon, and lime carries less sugar to soften it, so it usually tastes sharper.
4. Passion fruit. Titratable acidity 2.5 to 4.5 percent, citric with some malic. pH 2.8 to 3.3. One of the few fruits that is intensely sour and intensely sweet in the same spoonful.
5. Cranberry. Titratable acidity about 3 percent, split roughly three ways among citric, malic and quinic acid. pH 2.3 to 2.5, the lowest of any fruit here, which is why cranberries nearly always arrive with sugar attached.
6. Gooseberry. Titratable acidity about 2 percent, citric and malic. pH 2.8 to 3.1. The green ones are the tart ones; red and yellow gooseberries ripen sweeter.
7. Rhubarb. Titratable acidity 1.5 to 2 percent, mostly malic, with oxalic acid behind it. pH 3.1 to 3.4. Technically a vegetable, cooked as a fruit, and sour enough that every recipe for it starts with the sugar.
8. Kiwi. Titratable acidity 1.2 to 1.5 percent, a mix of citric, quinic and malic. pH 3.1 to 3.4. The quinic acid is the faint bitterness around the edge of the sour.
9. Green apple. About 1 percent malic acid in a Granny Smith; a red eating apple runs closer to 0.3. pH 3.2 to 3.4. The reference fruit for malic acid, which is why green apple is the name on half the sour candy in the aisle.
10. Pineapple. Titratable acidity 0.6 to 1.2 percent, mostly citric. pH 3.2 to 4.0. It also carries bromelain, an enzyme that digests protein, which is the tingle on your tongue that acid alone does not explain.
11. Strawberry. Titratable acidity 0.6 to 1 percent, mostly citric with some malic. pH 3.0 to 3.9. A strawberry's pH sits close to a pineapple's; it tastes sweeter because it carries less acid for the sugar it has.
12. Grape. Titratable acidity 0.4 to 0.8 percent in table grapes, tartaric and malic in roughly equal parts. pH 2.9 to 3.8. Wine grapes are picked far more acid than this; the grapes in the fruit bowl are bred for sugar.

Two more for the record. Blueberry: 0.3 to 1 percent acid, pH 3.1 to 3.3, mostly citric. Mango: 0.2 to 0.5 percent when ripe, pH 3.4 to 4.8, citric and malic. A green mango is a different fruit on this scale.

Why the sourest fruit is not the one that tastes sourest

Acid is half of sour. Sugar is the other half, and the ratio between them decides what you taste. A ripe strawberry and a lemon can land within a point of each other on pH, but USDA FoodData Central lists the strawberry at about 4.9 grams of sugar per 100 grams and the lemon at about 2.5. Food scientists call this the sugar-to-acid ratio, and it predicts flavor better than either number alone. It is also why tart fruits taste sourer underripe: the acid is there and the sugar has not arrived.

Water matters too. Most sour fruits are 85 to 92 percent water, and the acid is dissolved in it. Take the water away and the acid stays, so a freeze-dried piece carries the same acid as the fresh one in about a tenth of the weight. That is one reason freeze-dried fruit tastes sharper than the fruit it was made from, before anything has been added to it.

Where sour candy gets its sour

Read the back of a sour candy bag and the acids are the ones in this list, sold on their own. Citric acid for the fast hit, malic acid for the slow one, sometimes tartaric for the dry edge. The crystals on the outside are those acids mixed with sugar. What they are sitting on is usually gelatin and syrup, with the fruit part supplied by a flavor house.

They can also sit on fruit. Sour freeze-dried grapes start as a grape, which arrives with its own tartaric and malic acid, then are Infuz'd with sour, citric and malic, all the way through, and freeze-dried until they crunch. The ingredient list reads grapes first, then the sour. The rest of the REFRESH'D Sour Freeze-Dried Fruit lineup works the same way: five sour fruits, each with its own acid before anyone added any.

Picking a tart fruit for the sour you want

For a sour that hits and disappears, pick the citric fruits: lemon, lime, pineapple, strawberry. For a sour that lingers, pick the malic ones: green apple, rhubarb, an underripe grape. For sour and sweet in the same bite, passion fruit and tamarind lead the fresh fruit, and a sour-infused freeze-dried fruit does the same job without the spoon. The most sour fruit in the supermarket is the cranberry; the most sour fruit full stop is a tamarind pod, waiting in the international aisle.