Malting

The rst stage of malting comprises the steeping of barley in water at 14-18°C for up to 48 h, until it reaches a moisture content of 42-46%. Raising the moisture content allows the grain to start to germinate, a process that usually takes less than a week at 16-20°C. In germination, the enzymes break down the cell walls and some of the protein in the starchy endosperm (the grain's food reserve), rendering the grain friable. The amylases that break down the starch are produced (or released) in germination and these are important for the subsequent mashing process in the brewery, which is where they convert starch to fermentable sugars. Over the years a number of agents have been employed to assist the maltster to ef ciently produce malts that will satisfy the brewer in terms of quality and cost. In a great many markets these materials are banned, even though there is little or no evidence that they are harmful. Thus the natural gibberellin hormones of the barley, which have a key role in stimulating enzyme production, can be supplemented with gibberellic acid (GA), which is produced using industrial fermenta­tion processes (Tudzynski 1999). GA is very closely similar to the native molecules in barley, but nonetheless is outlawed in the Scotch whisky industry and the North American brewing industry. Where it is used, its undesirable impact in excessively stimulating the production of rootlets (which is a waste of potentially fermentable material) has been countered by the use of potassium bromate. A detailed study showed that this latter molecule does not survive in signi cant quantities into beer (Brewing Research International, unpublished). Very few malting operations nowadays use bromate, but it is widely used in the baking industry where it is used to help bread rise.
There was a time, long ago, when maltsters experimented with the use of formalde­hyde, as an agent to remove tannins from the surface of the grain and render the malt less prone to giving the beer a tendency to cloud (haze) formation (Macey 1970). I know of no maltster (or brewer) that has used this material for many years.
One recent development has been the proposal to seed barley with lactic acid bacteria during the malting process (Laitila et al. 2002). These bacteria are widely employed in the production of wholesome foodstuffs, e.g. sauerkraut and cheeses, and indeed natural infection of worts in German breweries has a very long history as an exercise in 'naturally' lowering the pH to a more favourable level. The rationale for using lactic acid bacteria in the maltings is that they will consume surface nutrients from the grain, thereby preventing undesirable organisms such as Fusarium from prospering.
Germination is arrested by kilning, in which there is a lowering of the moisture con­tent. Regimes with progressively increasing temperatures over the range 50 to perhaps 110°C are used to allow drying to < 5% moisture, while preserving those enzymes that are particularly sensitive to heat. The more intense the kilning process, the darker the malt that is produced and the more roasted, coffee-like and smoky are the avour char­acteristics developed. Essentially, malts used for making very pale lager-style beers are kilned quite gently, whereas those going into the somewhat darker ales are subjected to more heating. The very dark colours in stouts come from the incorporation into the grist of a proportion of malt that is roasted intensely.
One of the biggest concerns with the intense heating of grain raised over 20 years ago was the risk of developing nitrosamines (Havery et al. 1981). These molecules have been demonstrated to be carcinogenic in model animal systems, but not so far for man. They are primarily produced when precursors in grain, notably hordenine, react under heat with oxides of nitrogen, which tend to be present in the atmosphere, especially in regions with heavy industry. The malting and brewing industries responded with tremendous alacrity to the 'scare' and within a very short period of time nitrosamine levels had been reduced to very low levels (Sen et al. 1996, and see Chapter 5). The key change in practice was the use of indirect kilning such that the nitrogen oxides no longer contacted the malt.