The charge of green malt is fed into a rotating metal roasting cylinder which is heated so that the temperature of the green malt is about 55-65°C. At this temperature each individual grain is “mashed”, i.e. amylolysis and proteolysis takes place within each individual grain, yielding a complex mixture of simple and polymeric sugars and amino acids and peptides. Water is then removed from the grain and the product temperature raised to 120°-160°C. At this temperature the classic reactions of the non-enzymic browning process take place to form firstly glycosylamines and then ketosamines and eventually furan and pyran type heterocyclic oxygen compounds. By varying the time and temperature of the various stages a different colour range is produced.
Crystal or Caramel malts have a distinctive toffee flavour which becomes more intense as colour is increased, and at the higher end of the colour range burnt or roasted malt flavours may begin to appear. Traditionally in the UK, Crystal malt of colour 70-80 °ASBC has been used at about 5% of the grist to give the characteristic colour and flavour of UK Bitters and Pale Ales. By adjustment of the amount and/or colour of the Crystal malt some very distinctive beers may be brewed, but this may require some careful experimentation. Crystal malts have been used in the brewing of Lager beers, but considerable care is required to ensure that whilst a distinctive flavour is achieved, the crystal flavour and colour does not become too dominant. In all beers they can help prevent the formation of oxidised (cardboard) flavours.
