Glace de viande is brown stock reduced to its absolute essence — a dark, syrupy concentration that solidifies to a rubbery sheet at room temperature and shatters like glass when cold. It represents the ultimate extraction of flavour and gelatin from animal bones, reduced from litres to decilitres over hours of careful evaporation. The process begins with a finished, strained, defatted fond brun. The stock is brought to a gentle boil in a wide, heavy-bottomed pot (surface area accelerates evaporation) and reduced, skimming constantly as proteins concentrate and rise. At the halfway point, transfer to a smaller pot to prevent scorching as the liquid level drops. Continue reducing, lowering the heat progressively as the glaze thickens. The critical final stage requires constant attention: the bubbles change from rapid and small to large, slow, and volcanic. At this point, the glace is minutes from either completion or burning. Test by dipping a cold spoon — the glace should coat it in an opaque, dark film that sets firm within seconds. The reduction ratio is typically 10:1 — ten litres of stock yields one litre of glace. The finished product keeps refrigerated for months and frozen indefinitely. A half-teaspoon stirred into any sauce provides an intensity of meat flavour that no other ingredient can replicate. It is the secret weapon of the French professional kitchen.
Start with fully defatted, strained fond brun — any fat will concentrate and become rancid. Transfer to smaller pots as volume decreases — prevents scorching. Reduce heat progressively as concentration increases. Test on cold spoon — should set firm in seconds. 10:1 reduction ratio is typical.
Line a sheet tray with cling film, pour the hot glace in a thin layer, refrigerate, then peel off and cut into squares for portioning. Each square is approximately one tablespoon — store in a zip-lock bag in the freezer. For the richest possible glace, reduce a remouillage first and use that concentrated stock as the starting liquid for a second batch of fond brun before the final reduction to glace — a double-extraction technique used in three-star kitchens.
Reducing too fast over high heat — scorches the bottom, producing bitter, burnt glaze. Failing to defat the stock completely — concentrated fat turns rancid and gives an off flavour. Not transferring to smaller pots — the thin layer in a large pot burns before it concentrates. Using weak stock — concentrating mediocre stock produces mediocre glace.
Escoffier, Le Guide Culinaire; Larousse Gastronomique