What is Malt?
Malted barley (or malt as it is more commonly known) is one of the raw materials utilised by brewers & distillers for the production of beer & certain spirits. Barley (or other cereal grains) is turned into malt by allowing the grain to germinate under controlled environmental conditions, and then hot air dried to stabilize the internal biochemical processes and development of the characteristic flavour.
Starch contained within the malted barley is later converted into fermentable sugars in the brewing process. As well as starch, the malted barley also contains enzymes, proteins, vitamins & minerals.
There are three main stages of the malting process; steeping, germination, and kilning.
Steeping is performed to introduce sufficient moisture into the barley grain which signals and initiates the germination cycle of the grain to begin. The grain enters the steeping phase at a moisture of around 12%, and increases to a moisture in the range of 42-46% by the end of the phase, whilst generating heat and carbon dioxide during the process.
A steeping phase consists of the grain being immersed in aerated temperature controlled water for a period of time, then the water is drained off and the grain is allowed to rest whilst air is drawn through the grain and carbon dioxide is removed.
Steeping can take up to two days total, and a successful steeping phase is evident by the production of evenly hydrated grains that have the first appearance of coleoptile tissue (the ‘chit’) which signals that the germination phase has commenced.
The careful manipulation of moisture, temperature, and air flow parameters allow for the control of the germination phase of the process. Biochemical changes within the barley grain are essential for the successful conversion of barley into malt (collectively termed ‘modification’).
Modification occurs when the internally present hydrolytic enzymes catalyse the degradation of the starchy endosperm and cell walls in the presence of water.
Grain beds are watered and turned to allow greater air flow and also to break up any rootlets that become matted. The germination phase of the process can take up to 4-5 days depending on the type of final malt product produced.
The cessation of germination is brought about by the start of the kilning phase of the process. Kilning involves the hot air-drying of the grain that produces an easily milled final product. Further biochemical reactions occur that allow for the development of the characteristic colour and flavour of the malt, as well as reduce the content of enzymes present in the final product.
Kilning is carried out at Barrett Burston using single deck kilns, with the exception of the Perth Maltings, which has a unique double-decker kilning system.
Roasting is done in 4 distinct stages: steeping, germinating, roasting and cooling. At Barrett Burston Malting, grain spends 34-46 hours in steep tanks where we aim for a target moisture of 42-44%.
The grain is transferred to germination which lasts for around 4 days in Wanderhaufen style streets. This is a semi continuous moving batch germination process. Once germination is complete, the green malt is then transferred to the roasting drum.
The roasting takes place in two roasting drums. The average roasting time is 2 ½ – 3 hours with an air on temperatures of up to 460˚C. Our roasters take a batch size of 2.4 – 3.5 tonnes. The roasted malt is then transferred to the cooler and spends 35 – 60 minutes there in order to drop the temperature to <15˚C and fix the colour and flavour compounds. The malt is analysed before storage and thereafter awaits dispatch to our customers.