Process for the preparation of directly compressible mannitol having a content of the δ modification of greater than 90%, characterised in that a) a fluidised bed comprising very finely divided β-mannitol powder is produced by placing DC β-mannitol as bed in the processor and b) in a first step, as starting material, an aqueous D-mannitol solution, spray gas, the β-mannitol powder and hot air are combined, and c) the granular product formed falls into the fluidised bed, is taken up and fluidised, optionally, in one or more granulation step(s), sprayed with further liquid medium, dried and and transported further in the fluidised bed in the direction of the metering unit, and subsequently d) some of the unground material in powder and/or granular form is recycled into the process, where e) in the start-up process, the feed air to the grinding fan is dust-free, flap in the plant is closed and flap is open, and the air from the processor exhaust is withdrawn after the filters and f) a temperature of max. about 35 - 45°C and a spray pressure of max. 2.5 - 3.0 bar are set in the processor, where the D-mannitol solution is prepared from D-mannitol having a mannitol content of >98% by weight, and the recycling of unground powder takes place in an amount of about 3 times the amount, based on the amount of product withdrawn from the process, and the recycled powder takes path 9B/10B in the plant, with path 9A/10A closed, causing the formation of δ-mannitol to commence and the concentration of δ-mannitol to increase continuously under the conditions set, and g) when the content of δ-mannitol in the product formed has risen to about 60 - 70% by weight, the recycling of dust -containing feed air is switched over by opening flap and closing flap in the plant, causing the content of δ-mannitol to rise to greater than 90% by weight in the product. a) a fluidised bed comprising very finely divided β-mannitol powder is produced by placing DC β-mannitol as bed in the processor and b) in a first step, as starting material, an aqueous D-mannitol solution, spray gas, the β-mannitol powder and hot air are combined, and c) the granular product formed falls into the fluidised bed, is taken up and fluidised, optionally, in one or more granulation step(s), sprayed with further liquid medium, dried and and transported further in the fluidised bed in the direction of the metering unit, and subsequently d) some of the unground material in powder and/or granular form is recycled into the process, where e) in the start-up process, the feed air to the grinding fan is dust-free, flap in the plant is closed and flap is open, and the air from the processor exhaust is withdrawn after the filters and f) a temperature of max. about 35 - 45°C and a spray pressure of max. 2.5 - 3.0 bar are set in the processor, where the D-mannitol solution is prepared from D-mannitol having a mannitol content of >98% by weight, and the recycling of unground powder takes place in an amount of about 3 times the amount, based on the amount of product withdrawn from the process, and the recycled powder takes path 9B/10B in the plant, with path 9A/10A closed, causing the formation of δ-mannitol to commence and the concentration of δ-mannitol to increase continuously under the conditions set, and g) when the content of δ-mannitol in the product formed has risen to about 60 - 70% by weight, the recycling of dust -containing feed air is switched over by opening flap and closing flap in the plant, causing the content of δ-mannitol to rise to greater than 90% by weight in the product.