Glaces (glazes) appear throughout Escoffier's work as the concentrated foundation of classical sauce work. The French brigade kitchen maintained a constant production of glaces — brown, white, and fish — as the invisible infrastructure of everything that left the kitchen. A kitchen without glace was a kitchen working at a disadvantage. Pépin addresses them as both a technique and a necessary mise en place.
A perfectly made brown stock or white chicken stock reduced to one-tenth of its original volume — producing a concentrate of almost overwhelming flavour intensity that sets to a firm, glassy jelly and can be dissolved a tablespoon at a time to transform any pan sauce from adequate to profound. Glace de viande is the kitchen's amplifier. A single tablespoon added to a pan sauce, a soup, or a braise provides the resonant depth that hours of cooking would otherwise be required to achieve.
Glace achieves its remarkable flavour impact through the concentration of free glutamates, 5-nucleotides, and amino acid compounds — the same umami-building components that make soy sauce, miso, and Parmesan so potent, concentrated in this case by evaporation rather than fermentation. As Segnit notes, the combination of reduced stock and wine in a pan sauce is a pairing of glutamate amplification — both carry free glutamates that stack synergistically, and the wine's acidity simultaneously cuts the fat and heightens the perception of umami. A tablespoon of glace added to any such sauce multiplies this effect dramatically, which is why the brigade kitchen's investment in glace production was fundamental rather than optional.
**Ingredient precision:** - Starting stock: the best possible — see Entry 23 (fond brun) or Entry 4 (fond de volaille). A glace of weak stock is merely concentrated weakness; a glace of great stock is transformative. The gelatin content of the starting stock determines the final glace's body. - Reduction equipment: a wide, heavy-based saucepan — the wider the pan, the greater the evaporation surface area and the faster and more even the reduction. **The process:** 1. Begin with cold, defatted, strained stock. 2. Bring to a boil over high heat. Reduce to a simmer. 3. Skim frequently — as the stock reduces, fat and impurities concentrate at the surface. 4. As the stock reaches half its original volume: transfer to a smaller, heavy saucepan. The risk of scorching increases as the concentration increases — smaller vessels with lower surface area moderate this risk. 5. Continue reducing over medium-low heat, stirring more frequently as the liquid thickens. 6. At one-tenth of the original volume: the glace should coat a spoon thickly — like warm maple syrup — and when a small amount is cooled on a cold plate, it should set to a firm jelly within 60 seconds. 7. Pour into a container and refrigerate. At 4°C, the glace should be a firm, rubber-like block. Decisive moment: The transfer to a smaller vessel at the halfway point of reduction — and the increased vigilance from this point onward. As the concentration increases, the boiling point rises above 100°C and the rate of caramelisation accelerates dramatically. A glace that is not stirred constantly in its final stage will scorch at the base of the pan — and a scorched glace is ruined entirely, producing a bitter note that pervades every preparation it touches. Sensory tests: **Sight — the concentration stages:** At one-quarter volume: the liquid is noticeably darker and more viscous — it moves in the pan like a thin sauce rather than a liquid. At one-eighth: the surface shows slow, heavy bubbles rather than active boiling. At one-tenth: the surface appears almost still — the bubbles are few, slow, and large. The colour is very dark mahogany-brown, with a slight sheen. **The cold plate test:** At the suspected endpoint: remove a small spoonful to a cold plate. After 60 seconds at room temperature: it should set to a firm jelly that holds a shape when touched. Tilt the plate: the jelly should not slide. This test is the only reliable confirmation of sufficient concentration. **Feel — the finished glace:** At 4°C, the correct glace is a firm, dense jelly — it should require a knife or spoon to portion from the container, not pour. It should feel tacky to the touch — the same stickiness as concentrated gelatin at any temperature. **Smell:** The glace at correct concentration smells intensely of its source stock — a roasted meat depth (for fond brun glace) or a clean, sweet chicken depth (for volaille glace). It should smell rich and appetising, not harsh or burnt.
- Pour the finished glace into ice cube trays — each cube is approximately 15ml, the correct portioning unit for pan sauce finishing. Freeze and store in labelled bags; glace keeps frozen for 6 months - A cube of glace dissolved in 100ml of warm water produces a rapid stock substitute of credible quality for emergency sauce work - Glace de volaille added to a béarnaise in the final seasoning stage adds savoury depth without any discernible chicken flavour — it enriches without identifying itself
— **Scorched glace:** The reduction was not stirred sufficiently in the final stage. The base caramelised past the correct point and a bitter note has developed. Cannot be corrected — begin again. — **Glace that does not set cold:** Insufficient gelatin in the starting stock. The reduction has concentrated everything proportionally — including the lack of gelatin. A weak stock produces a weak glace. — **Grainy texture after refrigeration:** The glace was reduced too quickly at too high a temperature — the proteins denatured unevenly and the final product lacks the smooth cohesion of a correctly made glace.
Jacques Pépin's Complete Techniques