What process makes fat solid and more stable for cooking?

The correct answer is hydrogenation. This process involves the addition of hydrogen atoms to unsaturated fatty acids, which converts them into saturated fatty acids. By increasing the saturation of the fats, hydrogenation increases their melting point, making them solid or semi-solid at room temperature. This transformation also helps to improve the stability of the fats against oxidation, which is crucial for cooking applications where high temperatures are used.

Hydrogenation is commonly applied in the food industry to create products like margarine and shortening from liquid vegetable oils. The result is a fat that is not only solid but also has a longer shelf life and a texture that can be desirable in various cooking and baking applications.

In contrast, fermentation refers to a metabolic process that converts sugars to acids or gases, which does not directly relate to making fats solid or stable. Emulsification is the process of mixing two immiscible liquids, such as oil and water, but does not change the state of the fat itself. Oxidation involves the reaction of fats with oxygen, leading to rancidity and degradation, which is the opposite of making fats stable.