South African Pepper Steak Pie

Oxtail, shin and short rib all hold a lot of collagen. Collagen converts to gelatin slowly from 70 °C and much faster above 80 °C. The long braise dissolves it into the liquid.

Below approximately 40 °C, dissolved gelatin sets to a gel. So the chilled liquid sets to a firm jelly, and the fat rises and sets as a cap that lifts off in one piece.

The cold filling goes into the pastry as a solid. A solid filling gives off less steam and no free liquid while the base sets. In the oven the gel melts again and becomes the gravy.

This is why the filling must be cold, not warm, when the pie is assembled.

Puff pastry takes up water fast because it is thin layers of dough and butter. The base needs three barriers.

Blind bake. Heat drives water out of the pastry and sets the starch into a rigid structure before the filling touches it.

Egg white. Egg white proteins set from approximately 62 °C into a thin film that water does not easily cross. Brush it on the hot base so it sets at once.

Breadcrumbs. Dry crumbs take up the first liquid that meets the base.

The frozen assembled pie then goes into a hot oven on the lowest shelf. The butter in the pastry is still solid, so its water turns to steam and lifts the layers. The base gets direct heat before the filling warms enough to give off steam.

Reducing the wine by half in the open pot boils off most of the alcohol and concentrates its acid, sugar and tannin. In the closed braise the alcohol cannot leave, and a raw wine taste stays in the gravy.

Wine tannins bind to protein. Against the fat and gelatin of the filling they read as structure, not as bitterness.

Aluminium conducts heat approximately 200 times faster than borosilicate glass: approximately 237 W/m K against 1.1. On a preheated steel, heat goes through the foil into the pastry base in minutes. The base dries and its starch sets before the filling can wet it.

The frozen puck delays the filling. It must take up the heat of melting, approximately 334 J/g of water, before the gelatin can melt at approximately 35 to 40 °C. During that time the base bakes with nothing wet against it.

The cold puck also keeps the fat in the base pastry solid until the pie goes in the oven. Solid fat lets the water in the dough turn to steam between the layers, so the base puffs and does not go leathery.

Tendon is almost pure collagen, packed tightly and bonded across its fibres. The bonds get stronger as the animal ages and as the muscle works. They resist heat much more than the loose collagen around the muscle cubes.

A 3 h braise softens the cubes but only starts on the tendon. In an earlier cook, tendon from a braise stayed chewy.

Cook the tendon whole in the stock overnight, at a light simmer. Cut it when it is cold and set. Add it to the meat after the braise, so it does not cook a second time and fall apart.

Cornstarch is approximately 25 percent amylose. Amylose is a straight-chain starch. In the cold and during freezing, the chains line up again and push water out of the gel. The gravy then weeps. This is retrogradation.

Gelatin sets by a reversible network. Ice can loosen it a little, but it melts back into gravy in the oven.

So this filling gets its body from reduction only: oxtail, tendon, the reduced stock and the demi-glace.