Almond flour vs plain flour
Not a flour with the gluten removed — a nut with no starch in it at all, which is a much larger difference than the name suggests.
The short answer
The word “flour” does a lot of misleading work here. Wheat flour is mostly starch with some protein; almond flour is mostly fat and protein with essentially no starch. That means it supplies neither of the two things a wheat flour supplies to a bake — no gluten network and no starch to gelatinise and set — and it adds a large quantity of fat that was not in the formula before. Substituting it one-for-one produces something dense, greasy and often raw in the middle. Where it works, it works because the recipe was designed around it: a frangipane, a macaron, a friand, and cakes where eggs are carrying the entire structure.
Where they differ
| Dimension | First | Second |
|---|---|---|
| Main constituent | Fat, then protein. Very little carbohydrate. | Starch, then protein. |
| Gluten | None. It is not a grain. | Forms the network most baking is built on. |
| Starch to gelatinise | Essentially none, so nothing sets as it cools. | The main setting mechanism in a cake. |
| Effect on the formula | Adds a great deal of fat that was not accounted for. | Contributes almost no fat. |
| Keeping | Shorter — the nut oil goes rancid, and cold storage helps. | Long, if kept dry. |
| One-for-one substitution | Dense, greasy, frequently underset in the middle. | — |
Ground almonds and almond flour, and whether the difference matters
In British usage “ground almonds” usually means whole almonds with the skins on, ground to a medium texture; “almond flour” usually means blanched almonds ground finer. American usage tends to reserve “almond meal” for the first.
For a frangipane or a cake the difference is cosmetic — slightly darker, slightly coarser. For a macaron it is not: the shell's smooth surface depends on a very fine, skinless grind, and skin fragments show as specks and can puncture the shell as it rises.
So the honest answer is that the two are interchangeable in most things and not in the one bake people most often ask about.
Related
Compares
Not a flour with the gluten taken out: a nut with no starch in it, which is a much larger substitution than the name suggests.
Not a flour with the gluten taken out: a nut with no starch in it, which is a much larger substitution than the name suggests.