How did nouvelle cuisine use reductions instead of flour-thickened sauces?

In nouvelle cuisine, chefs moved away from the traditional grande cuisine practice of using flour-based roux to thicken sauces, which was often viewed as heavy and calorie-laden. Instead, they utilized the technique of reduction to achieve the desired consistency and flavor intensity.1234

By simmering stocks and cooking liquids over heat for an extended period, the water content evaporates, naturally concentrating the flavors and thickening the liquid into a more refined, syrupy consistency. This method emphasizes the natural essence of the ingredients rather than masking them with the starchiness of flour. This shift was part of a broader philosophy within nouvelle cuisine that prioritized lightness, freshness, and clarity of flavor, directly reacting against the rigid, fat-heavy systems codified by earlier chefs like Auguste Escoffier.3514