glace or “half-glace,” which is stock simmered down to 25–40% of its original volume, often with some tomato puree or paste to add flavor and color, and with some flour or starch to supplement its lower gelatin content (10–15%) The tomato particles and flour gluten proteins cloud the stock and are removed by skimming the stock as it reduces, and then by a final straining The starch in demi-glace, around 3–5% of its final weight, is largely an economy measure — it gives a greater thickness with less stock reduction and loss of volume to evaporation — but it also has the advantage of sparing some of the stock’s flavor from being boiled off, and avoiding the sticky consistency of very concentrated gelatin Demi-glace is the base for many classic French brown sauces, which are given particular flavors and nuances with the addition of various other ingredients (meats, vegetables, herbs, wine) and final enriching thickeners (butter, cream) Because they’re versatile but tedious to prepare, demi-glace and glace are manufactured and widely available in frozen form Concentrating Stock and Flavor to Finish a Dish An alternative to cooking stock down in bulk is to reduce it in small quantities to augment the pan juices of a roast or sauté Once the meat is cooked and its juices concentrated and browned on the pan bottom, the cook can repeatedly add a small quantity of stock to the pan and cook it down until its solids begin to brown, then dissolve the successive brownings in a final dose of stock to make the liquid sauce The high pan temperature helps break down the gelatin molecules into shorter lengths, so the resulting sauce is less sticky and congeals more slowly than it would if the gelatin were intact ... augment the pan juices of a roast or sauté Once the meat is cooked and its juices concentrated and browned on the pan bottom, the cook can repeatedly add a small quantity of stock to the pan and cook... it down until its solids begin to brown, then dissolve the successive brownings in a final dose of stock to make the liquid sauce The high pan temperature helps break down the gelatin molecules into shorter lengths, so the resulting...thickeners (butter, cream) Because they’re versatile but tedious to prepare, demi-glace and glace are manufactured and widely available in frozen form Concentrating Stock and Flavor to Finish a Dish