Fire crews were called to the Trafford park site at 4.52am on Saturday (June 22).
It is believed that Corn Flakes became jammed in a conveyor belt inside an industrial oven and caught fire.
Station manager Paul Smitham said: “The fire spread through the big ovens and into some ducting in the factory. It was quite difficult because the fire was on the fifth floor.”
Fire crews needed to wear breathing apparatus to tackle the blaze.
The 70 members of staff had already been evacuated from the building by the time fire crews arrived.
One man was given oxygen therapy after suffering the effects of smoke inhalation. No-one else was injured.
The firm said there was “no loss of production” and that the fire service left “within an hour”.