Bee bread is the pollen which the bees process in their hives. Bee bread has a different composition to the bee pollen and/or floral pollen.
Elton Herbert Jr. writes in the last edition (1992) of “The Hive and the Honey Bee”, p.202:
“Pollen pellets collected by foragers are packed in cells by the honey bees, with a small cover of honey and glandular secretions added to the mass of stored pollen. This store of pollen is called “bee bread”. Because different pollen loads are mixed in storing, the cells are stratified. Stored pollen becomes non-viable in 1 to 8 days depending on the plant species. Probably substances secreted by the honeybees to moisten the pollen while packing it in the comb are responsible for the rapid loss of germination capacity. The mandibular glands of honeybees also produce a germination-inhibiting factor. Stored pollen undergoes a number of biochemical changes which may be responsible for increased stabilisation of the product or may lead to chemical changes that increase the digestibility and nutritive values for bees.”