Drying of Beef in Superheated Steam

摘要

Two drying treatments were applied to slices of beef: superheated steam and hot air. Drying kinetics and quality attributes such as color, water activity, and peroxide value were investigated for different drying conditions (drying medium temperature 130, 160, or 180° C; flow rate of the drying medium of 35, 45, or 55kg/h; and sample thickness 3 mm, 6 mm, 9 mm, or minced beef). The experimental results show that superheated steam drying generally leads to shorter residence times in the dryer when the moisture content needs to be decreased below 8%. Superheated steam drying distinguishes itself by longer constant rate periods, lower critical moisture contents, and higher drying rates for the falling rate period compared to air drying. Reducing the sample thickness or increasing the transferred heat, by increasing the temperature or velocity of the drying medium, result in accelerating the drying process. Temperatures above 160°C, however, cause changes within the and its surface and prevent the bound moisture from getting to the meat's surface to evaporate. This so-called case-hardening effect is worse for air drying than for superheated steam drying and results in even longer drying times and higher final moisture contents. Superheated steam drying reduces the water activity faster than air drying at the beginning of the drying process, but the same values are reached at the end of the drying run. Furthermore, the study proves that the absence of oxygen during superheated steam drying leads to prevention or minimization of lipid oxidation reactions, thus resulting in low peroxide values. Undesired quality changes like off-flavors and off-odors hardly develop during superheated steam drying even at high temperatures and long drying times.