4. Freeze-drying

This drying technique is of interest for products with a reputation for being heat-sensitive, particularly in pharmaceuticals (active ingredients), despite its high energy cost and the relative slowness of the drying process, which is generally batch-type with long residence times. Continuous processes have also been developed for certain applications (e.g. soluble coffee). It is also a technique for preserving the initial volume and appearance of the product, which has become porous and easy to rehydrate (so-called "instant foods").