The freezing of unpackaged foods induces water loss due to interactions with the surrounding medium. The weight loss resulting from this dehydration is up to 6% according to the product and the freezing process. Food dehydration was studied for various operating conditions from mechanical to cryogenic ones with the same freezing device using Tylose as a food model material. The dehydration was studied for several surface states (smooth or streaked surface) and product porosities (full or perforated plates). It was found that weight loss is estimated with a good reproducibility in the developed freezer. The influence of freezing operating conditions and product characteristics on weight loss were clearly pointed out. From these results, weight loss could be related to the surface temperature evolution. In any case, these results confirm that to limit the weight loss, it is essential to decrease as quickly as possible the surface temperature of the product.