Brewing trials using lager malt with rice adjunct, in which rice constituted from 20 to 80% of the grist, are described. It was found that malt/rice grists have a lower hot water extract than all malt grists and produce worts of lower gravity and with less free amino nitrogen. Because rice starch has a fairly high gelatinization temperature (varying from 62 to 75 degrees C, according to the variety), at which malt amylases are liable to be inactivated, the adjunct should be cooked with a thermostable industrial amylase before adding it to the malt mash. It may also be necessary to include a proteolytic preparation, since if the mash contains large quantities of rice, the protein content of which is not readily degraded by malt proteolytic enzymes, the wort may contain insufficient free amino nitrogen, leading to malnutrition of the yeast and consequent fermentation problems, unless the rice proteins are broken down by added enzymes. Even with the use of a proteolytic preparation, it was found difficult to achieve adequate free amino nitrogen levels in worts made from mashes containing over 50% rice. However, the results achieved were considered acceptable in other respects, even using very high percentages of rice.
Keywords : adjunct brewing free amino nitrogen mashing properties proteolysis rice wort