Starch Drying: Equipment Selection

There is one hard limit in starch drying: gelatinization. Once the moisture inside a starch granule reaches a certain fraction, the granule takes in water, swells and its structure breaks down, and after gelatinization it cannot be reversed — what comes out is a viscous paste rather than a powder. Starch is therefore rated at the highest heat sensitivity level and the process only works on a flash airflow line, where the water is taken out in the seconds before gelatinization can start. Our configuration works backwards from the material temperature: the hot air can run at 180 to 200°C and the residence time is only a few seconds.

There is one hard limit in starch drying: gelatinization. Once the moisture inside a starch granule reaches a certain fraction, the granule takes in water, swells and its structure breaks down, and after gelatinization it cannot be reversed — what comes out is a viscous paste rather than a powder. Starch is therefore rated at the highest heat sensitivity level and the process only works on a flash airflow line, where the water is taken out in the seconds before gelatinization can start. Our configuration works backwards from the material temperature: the hot air can run at 180 to 200°C and the residence time is only a few seconds, so as long as the moisture comes off fast enough the material temperature never reaches the gelatinization point. Starch also has a characteristic that matters here: gelatinization temperatures differ widely by species — cassava, corn and wheat starch are not the same — so the set temperature cannot simply be copied from another batch and has to follow the incoming test data. Storage matters just as much: starch takes on moisture very quickly, and once it cakes and turns sticky the drying has been wasted.

Why can starch not be dried in a rotary drum?
Because the residence time in a drum is minutes, and the gelatinization risk comes precisely from residence time. The hot air can be hot, but the longer the material stays in the machine, the more heat eventually reaches the inside of the granule and opens its structure. The seconds-long heating of a flash airflow line is the only route that holds this line.

Can the same temperature be used for every type of starch?
No. Gelatinization temperatures differ widely by species — cassava, corn and wheat starch are not the same — so the set temperature cannot simply be copied and has to follow the incoming test data. This has to be confirmed before the order is placed.

Why does starch need moisture protection after drying?
Because starch takes on moisture very quickly, and once it cakes and turns sticky the drying has been wasted. Storage and transport need to be sealed and conditioned; the moisture at the moment the product leaves the machine is not the whole story.