Allspice vs Black pepper
The short answer
Related only by the word "pepper" and by history. Allspice is a New World berry named pimenta by Spanish traders who thought they had found pepper, and English kept the resemblance in "Jamaica pepper" and "myrtle pepper". It has no piperine, so it is not pungent at all: its warmth is eugenol, the clove compound. Black pepper contributes bite; allspice contributes sweet aromatic warmth. Substituting either for the other changes which of those two things the dish has.
Side by side
| Allspice | Black pepper | |
|---|---|---|
| Botanical identity | Pimenta dioica (L.) Merr. | Piper nigrum L. |
| Part used | berry, fruit | fruit, berry |
| Origin | The Greater Antilles and Central America, with Jamaica the historic and still the most reputed source. | The Malabar coast of southwestern India. |
| Flavour notes | warm, sweet, clove-like, cinnamon, peppery, woody | pungent, woody, citrus, resinous, warming |
| Heat | Scoville does not apply | Scoville does not apply |
| Flavour | Sweet, warm and gently pungent, reading as clove first, then cinnamon, then a faint pepperiness. It is milder and rounder than clove and much easier to use in quantity, which is why it can carry a dish where clove can only accent one. | Pungent and warming with a woody, faintly citric aroma behind the bite. The pungency builds and lingers rather than striking immediately as chilli heat does. |
| Aroma | Warm and sweet, clove-dominated with clear cinnamon and a light peppery edge. The impression of several spices at once is genuine rather than suggestible — the oil contains the compounds that dominate each of them. | Woody, resinous and citrus-fresh, with a distinct piney lift that is lost quickly once ground. |
Which should you buy?
Allspice
Buy whole. Allspice keeps unusually well in the berry, grinds acceptably at home, and is used whole in a great many of its traditional applications — pickling, brining, braising — where it needs to be retrievable. Ground allspice also loses the specific thing that makes it worth having: as the lighter aromatics go, it converges on a flat clove note, and at that point you may as well have used clove.
Black pepper
This is the least ambiguous whole-versus-ground case in the entire spice cupboard. Pepper's pungency is non-volatile and its aroma is highly volatile, so pre-ground pepper reliably delivers the heat and reliably loses the fragrance. Buy whole and grind at the point of use; nothing else about pepper matters as much.
Full detail on allspice and black pepper, including evidence grades and sources for every claim above.