Sugna

A whole-muscle ham dries through its surface, and a boned or trimmed ham has two surfaces that behave completely differently. The skin and fat side is almost impermeable, so very little moisture leaves there. The exposed lean face, where the leg was cut and trimmed, is wide open. Left alone, that face loses water far faster than the deep interior can resupply it, and the result is the classic fault: a hard, dark, leathery rind sealing the outside while the centre is still at a water activity that will spoil. That is case hardening, and sugna is the traditional answer to it.

Sugna is a paste. The base is pork fat, usually rendered leaf lard or a soft back fat, worked with flour, most often rice or wheat, and salt, sometimes with black pepper and occasionally a little of the ham's own trimmed fat. The proportions vary by house and by region and the texture is what matters more than the ratio: it should be stiff enough to stay where it is put on a vertical face and soft enough to smear into every crevice without air pockets. It is applied by hand, in a layer of a few millimetres, over the exposed lean only. The skin side is left bare because it does not need help.

What the layer does is slow the face down rather than stop it. Fat is a poor barrier to water vapour compared with plastic but a very good one compared with bare lean, and the flour gives body and a degree of breathability. The face keeps losing moisture, just at a rate the interior can keep pace with, so the moisture gradient through the ham stays gentle and the whole leg dries evenly. The Italians call the operation sugnatura and time it precisely: for Prosciutto di Parma it comes after the initial resting and salting phases, once the surface has firmed but before the long ageing, and the exact timing is part of the protected specification.

It is not a preservative and it is not a mould coating, though it interacts with both. The salt and the pepper in the mix discourage surface growth, and the layer physically excludes flies and limits the surface a mould can colonise, but the preservation is being done by the salt in the meat, the drying and the temperature. Sugna also protects against the other surface fault of a long dry: the exposed lean going rancid and dark from oxidation.

The same idea appears under other names across the ham traditions. Spanish producers grease exposed lean on serrano and iberico legs, the French and Corsican hams use the technique, and speck and cecina specifications allow for sugna or an equivalent protection on cut faces. Where a Curesmith recipe lists sugna in its formula, it is listed as a process material rather than an ingredient: it goes on the outside, most of it is scraped off before slicing, and it is not eaten as part of the product.