Q: We use an infusion mashing vessel with a deep 3 foot bed. We are having problems running off wheat beers with more than 20% wheat grist. What options exist to make this easier?
A: Infusion mash tuns were designed to make all-barley malt mashes in British brewing. The barley used is normally very well modified and crushed more coarsely than a typical North American malt to form the grist. The coarse grist including the non-soluble husk and gentle infusion mashing are able to form a permeable mash bed that is relatively deep and does not require rakes to facilitate run off. Wheat (and rye) malt does not have a husk and the grain is usually not very well modified meaning that it not only does not help in forming a filter bed and has greater amounts of beta glucan material that will increase the viscosity of the wort. Beta glucan in malt is the cell wall material that encases the starch granules in the barley grain, it is partially broken down during malting in the germination process. Large amounts of wheat and rye in the grist will tend to decrease permeability and yield run off problems. There are two options commonly used to alleviate the issue of slow run-offs with high wheat or rye malt grists. One is to add rice hulls to the grist which will help in forming a more permeable mash bed but this will not decrease the beta glucan present so it only offers a partial solution. The other option, which can be used in conjunction with rice hulls on on its own, is to use a glucanase enzyme that will break down the remnant beta-glucan material in the mash. By breaking down this material the viscosity of the wort will decrease significantly and the run-off is much easier even with higher wheat and rye grists. The enzyme is deactivated during the subsequent kettle boil. b Either way look for barley malt specifications limiting the barley beta glucan levels to less than 100 ppm.