An apparatus for the heat treatment of a product, in particular a product contained within a hermetically sealed pouch or other plastic container, the apparatus comprising, a heating unit (T1, T2) to contain a product as product is brought towards a treatment temperature and pressure, a sterilisation unit (10) to contain product at a pre determined treatment temperature and pressure to sterilise product, and a cooling unit (T7-T9) to bring a product from said treatment temperature and pressure towards ambient; each unit being selectively sealable from another unit, the apparatus further comprising: a plurality of conduits (29, 32) carrying heat-exchange fluids allowing heat to be transferred between units; and comprising a heater (26), preferably producing steam, to supply heat to the apparatus; a heat-exchange unit (21) enabling heat energy to be transferred from one conduit to another; a hot well (28) to retain a reservoir of heat exchange fluid at the highest temperature required by the apparatus.