The concasse technique is among the most specialized cutting board skills a chef can learn. Short for concasser, the French verb "to pulverize," this culinary technique is employed to remove the seeds and skin from certain kinds of fruits and vegetables. These are then reduced to clean, diced cubes for use in sauces, soups or salsa. This is also a French way to describe the process of turning a medley of spices into a single powder in a mortar and pestle or spice grinder.
Tomatoes are perhaps the most prime candidate for the concasse treatment. The flesh is so different in texture from the meat, and the seeds are so regularly disdained. Other fruits and vegetables are peeled, seeded and diced, from apples and oranges to cucumbers and squash.
The concasse process will be slightly different for each type of produce. For harder vegetables and fruit, the skin can typically be removed with a peeler or by hand. For the tomato, the process is different, since the skin is so delicate. First, the tomato is cored and scored on the bottom with an "X." Then, the tomato is blanched, for just 10 or 15 seconds, in simmering water until the skin starts to peel off.
To finish off the concasse process on the tomato, it is cooled in ice water to stop the cooking process. Then, the skin is peeled off where the "X" was scored, and the tomato is squeezed to remove the seeds inside. Once the seeds are gone, the tomato can be diced into small, uniform-looking cubes or pulverized with what is known as a rough chop. To skip the blanching all together, the fruit or vegetable can be peeled with a jagged potato peeler.
The same idea is behind another concasse procedure to make a spice blend. Hard, whole spices like peppercorns, star anise, allspice, cloves and mustard can be thrown together into a grinder or mortar bowl. A pestle or the grinder's blades then turn the mixture into a single, powdery blend.
Chefs are more likely to learn the concasse method after having perfected some of the more basic knife skills. A rough chop has no organized pattern, but a dice or fine dice requires some forethought to get the pieces of near-equal size. To mince, cooks must turn fruits, vegetables or herbs into tiny same-sized pieces that will spread the furthest throughout a recipe. The julienne technique is employed to add visual appeal, creating squared-off strips about the size of standard matchsticks.