UHT processing involves the heating of milk to a high
temperature during a short time in order to obtain a
product with a long shelf life at room temperature.
During the process, most bacteria are inactivated but
heat-stable enzymes of native or bacterial origin can
survive and give rise, during storage, to both gelation
and o-¯avours (bitter, stale and oxidised) (Burton,
1988). Gelation and bitterness are usually related to
protein breakdown (Harwalkar, 1982). UHT milk
odour has a ``cooked'' note in the freshly prepared
samples, which afterwards evolves to a ``¯at'' character
(Mehta, 1980). Other objectionable o-¯avours can
then begin to develop.