the temperature of bakery products is reduced immediately after the discharge thereof from the oven , by means of vacuum , by first subjecting the bakery products to a substantially linear pressure reduction as a function of time at a rate of not more than 60 mm hg per second through at least half of the total pressure drop to be achieved . the pressure reduction rate is then allowed to increase substantially for a terminating vacuum treatment . at least one vacuum chamber is provided and is adapted to be connected to a source of vacuum though a vacuum conduit and a valve , and has a closeable opening for bringing bakery products into and out of the chamber . in the vacuum conduit , in parallel to a servo - valve serving to apply a full vacuum effect from the source of vacuum during the remaining portion of the total pressure drop , there is inserted a by - pass conduit having a permanently open cross - section which can be adjusted to provide the substantially linear pressure reduction .