The Malting Process

 Thomas Fawcett & Sons Ltd

The Production of Malt

There are three stages involved in converting barley to malt, namely steeping germination and kilning the overall objective being to provide the brewer with a convenient form of starch and enzymes.

The purpose of steeping is to achieve an optimal moisture level in the grain normally between 44% and 46%. Previously dried and cleaned barley is soaked in large vessels, usually with conical bottoms for ease of emptying. Normal steeping regimes are between 48 and 72 hours dependant on what is required from the finished malt. This is split between wet steeping (i.e. soaking in water) and dry periods or air rest when the water is drained off.

Aeration and C02 extraction is also normally carried out during steeping.

Once steeped the barley or green malt as it is now known is transferred into a vessel for germination. Here cooled, humidified air is blown through the grain bed to maintain the moisture level close to that reached in steeping. Further the cooled air maintains the grain at a consistent temperature between 59°F and 64°F (15°C – 18°C) During this period the grain is allowed to develop a root and the acrospire grows between 3⁄4 and full length of the kernel without actually sprouting. Two major changes occur: Firstly enzymes are developed which break down the cell walls. The cell walls are made up of gum substances insoluble in water, the action of these enzymes gives us freely available starch. Secondly other enzymes are produced which break down proteins. Further enzymes are developed which will convert the starch into fermentable sugars in the mash tun later on in the brewing process. These changes are known as “modification” and the Maltster controls these changes by means of time, temperature of the processing and moisture content in the grain. Germination times can be as short as 84 hours or up to 144 hours.

Here the malt is dried out to make it stable and safe for storage. Subtle biochemical changes take place in the latter stages, which give malts their characteristic flavours and colour. A combination of high moisture and high temperature will destroy the enzymes developed during germination, which is not desirable. To prevent this happening relatively low temperature inputs along with very high air flows are needed in the first 24 hour of kilning. When the malt becomes “hand dry”, around about 6% moisture content, the temperature can be increased culminating in air on temperatures between 203°F and 212°F (95°C – 100°C) in the case of ale malts for colour to develop. Lager malts are produced at lower final temperatures usually 183°F – 185°F (84°C – 85°C) resulting in higher enzyme levels and lower colours in the finished product.

Selecting Barley with good Malting Qualities

The suitablility of a barley for the production of quality malt is dependent on a number of factors.

Most important are:
regularity of size, shape and colour
fitness of skin and freedom from damage
suitable nitrogen content
condition and appearance of the endosperm cot
varietal purity
freedom from other seeds and moulds

This is largely a matter of experience and judgement. Tied up with mellow colouring and pigmentation along with varietal differences. Best malting barley should be well filled, plump and mellow in colour.

This is observed by cutting the barley in a farinator. Best malting barley should have a mealy or creamy white endosperm cut. Partly steely (grey) or steely cuts do not indicate definitely poor malting quality barley but do not give indication of good qualities as do mealy grains. Steely grains normally contain high nitrogen levels.

The husk belongs to the leaf system of the grain amd should be fine and “thin” in appearance. Luxuriant husk indicates over fertilising and coarse grain. Normally for best quality the husk should be shrunk and slightly shrivelled onto the grain. Stretched husk may be an indication of excessive late growth of the kernel.

Better malting qualities are short and plump with a large scutellum, i.e. the bulk of the endosperm is near to germ or source of enzyme and the enzyme has a large channel to the endosperm – as opposed to long spindly grains with narrow scutellum. Bold plump well matured grains give higher extract but thinner pinched grains give higher diastase.

All the above characteristics need to be regular to give even malting growth. The prime factor here is the purity of race. Irregularity is particularly noticeable in grain after dry growing seasons or when grain has been harvested too early.
Damage includes that caused by weather, fungi, insects or too close combine settings. Heat damage is more dangerous and is normally caused by storing wet grain at high temperatures. Under those conditions spoilage can be very rapid. Detection is quite easy by discoloration or destruction of the embryo. The danger is reduced grain vitality or indeed complete loss of it, Germinative energy needs to be a minimum of 96%.


Points to note are:

1. Plump grain of even size with a “thin” skin.
2. Mature even coloured sample.
3. Lack of damage grain either from heat damage or otherwise.
4. Freedom from small or immature corns.
5. Mealy endosperm cut.
6. Freedom from moulds or other off flavours or taints.
7. Minimum 96% germinative energy.
8. Suitably low in nitrogen, normally about:
1.50 for Best Pale Malts
1.65 for Mild Ale Malt
1.70 for Crystal Malt
1.75 for Chocolate Malt or Roasted Barley

Coloured Malts

Coloured Malts can be summarised under four main headings:

Crystal Malt
Black Malt
Chocolate Malt
Roasted Barley

There are others such as Amber, Brown and Pale Chocolate but these are much more rarely used.

Coloured Malt is used in the Brewery primarily, to add natural flavour and colour. It has strong characteristics and great care is required to find the correct blend.
Coloured Malt usually makes up between 5% and 10% of the total grist. It should be noted that coloured Malts are normally free from enzymes and nitrosamines due to the higher than normal processing temperature. When producing beers with a high coloured malt (or indeed adjunct such as wheat, maize, rice, sugar etc) content optimal brewhouse performance can only be achieved by the addition of mash enzymes.

Whilst colour is important, the production of flavour is the primary reason for using these types of Malt. Consequently these products should always be freshly roasted. Aroma is readily lost in storage and this is a commodity that is best produced to order.

For the manufacture of coloured Malt, as with any other, the selection of barley is all important. An even, uniform sized barley, well filled with minimum damage and a good husk is required. With the exception of Roasted Barley, all the other coloured Malts need to be steeped and a minimum germination rate of 96% is necessary. It is a popular misconception that damaged or spoilt grains, or grain with poor germination potential can be used for coloured Malts. This strictly is NOT the case – good quality malt is only produced from good quality barley. Indeed even in the case of Roast Barley the potential for good even germination is essential. Evenness of roasting is the objective and this can only be achieved with a uniform and sound raw material.

To summarise, an even looking sample of barley is required, the nitrogen of which should not be too low in the case of Black or Chocolate Malts. Otherwise this would lead to a soft Malt with a tendency to split and stick together which is not desired.
Conversely a barley with too high a nitrogen, although taking colour readily, can char easily and change to carbon which is insoluble resulting in a loss of extract and colour. A nitrogen content between 1.65 and 1.75 would be satisfactory for Black and Chocolate, whereas for Crystal this would be between 1.55 and 1.70 in order to obtain the high degree of modification required.

The roasting process itself is carried out in drums with either direct or indirect heating. The drums are usually about 6ft long and 4 to 5 ft diameter. These are fitted with metal scrolls or paddles which turn and mix the grain throughout the drum ensuring even roasting. In the case of Black, Chocolate and Roasted Barley the drums have to be fitted with a central watering pipe to arrest the process once the desired degree of roasting has been reached. Normally 15 gallons of water is used.

The Production of Coloured Malts

Chocolate and Black

This is basically the same product, the difference being in the final colour achieved. The Malt is normally steeped, germinated and kiln dried to a moisture of about 4% – 5%. Overgrowth at this stage is to be avoided otherwise this can lead to sticking or the formation of “Blackberries”, during the roasting process. The Malt can be quite safely stored in bins at this stage prior to roasting. The actual roasting process takes between 21⁄2 to 3 hours with a final temperature between 400°F and 420°F (205°C – 215°C) in batches of 0.75 tonnes finished malt. This entails a gradual heating up to 400°F (205°C) which takes about 2 hours followed by high temperature roasting where the temperature is maintained between 400°F and 420°F (205°C – 215°C) until the desired degree of roasting is reached. The malt is then quickly quenched with water to arrest the roasting and also to ensure the Malt is sufficiently cooled on discharge to avoid any danger of flashback. It is then left for a further 15 to 20 minutes to dry to a moisture content of between 1.5% to 3%. Typical analysis for Black and Chocolate Malt would be an extract figure of between 257 and 267 ld/kg (litre degrees per kilogram) with a colour for Chocolate between 900° and 1100°, Black being 1200° to 1400°.

Roasted Barley

This is produced in much the same way as Chocolate and Black with the exception that there is no initial steeping or germination. The actual process takes slightly longer than Chocolate and Black, normally carried out about 10° higher in temperature. Extract falls somewhere between 260 and 270 ld/kg. The most noticeable difference is in flavour. Roasted Barley has a sharper and dryer flavour to that of Chocolate or Black.

Crystal Malt

This is probably the most widely used of all the coloured Malts and is made from fully modified Malt produced in much the same way as ordinary Ale Malt. Growth is a little more forced with germination taking place at a high level of moisture (about 47%), and at slightly warmer temperatures, typically 68°F (20°C). Higher moisture and higher temperature ensure a high level of readily formed sugars. Unlike the Black and Chocolate, Crystal Malt is roasted straight from the germination vessels (as green malt).

Germination time is normally six days. Again processing takes place in a roasting drum in batches of about 1.75 tonnes roasting is split into three fairly distinct phases.

1. Stewing to ensure good saccharification of the starch.
2. Drying.
3. Roasting where the actual colouring takes place.

Normally this takes about three hours for each batch within the temperature range 120°F to 280°F (49°C – 138°C). Air flow is normally minimum during the stewing phase but in the second two phases air flow requirement is maximum when the heated air is passed directly through the green malt in order to promote rapid drying. In the final phase the kernels can be heard popping or cracking in the roasting drum w/hen colouring and swelling takes place.

The colouring is caused by the caramelisation of the lower molecular weight starch, when subject to higher temperatures. It can be appreciated that it is a very different product from those previously described. Liquefaction and saccarification are much enhanced to those normal malts. Indeed when the machines are discharged to the cooling tray the endosperm’s are predominately liquid setting to a toffee like product on cooling.

Colour range on the finished product can be very wide, varying from about 25°at the bottom end of the scale up to 400° at the top, dependent on Brewery specification. Extract would be slightly higher than the Black Malt in the range of 260 – 275 ld/kg with a moisture content of between 2% – 4.5%. An important point from a flavour consideration is the degree of crystallisation of the endosperm at the end of roasting. Ideally this should be crystallised as closely as possible to 100% but commercially crystallisation of 90% or greater is quite acceptable. Anything less than this would alter the flavour profile considerably and instead of having a clean sweet flavour this would become dry and biscuity and much more like Amber Malt than Crystal Malt.

As in most things these days Malt roasting is subject to change, however, quality Malt roasting is still extremely dependent on the human element.

In the production of all the Malts described, regular samples are taken from the machines and cut in a farinator which gives a cross sectional cut of the Malt. It is only the roaster’s experienced eye which can produce consistent quality roasted Malts to order.

Environmental problems connected with Malt roasting, particularly Black Malt and Roasted Barley can be extremely serious due to the reek given off and the fall out produced by high temperature roasting. Afterburners are normally used to treat the flue gases However these are expensive to buy, expensive to run and as yet not by any means completely satisfactory. Ideally a roasting house should be sited five miles from the nearest habitation, failing that it is recommended that the site by triangular in shape being bounded on one side by a coke oven, on the second by a chemicals works and on the third by a cemetery…