Malting is the process of

steeping Steeping is the soaking of an organic solid, such as leaves, in a liquid (usually water) to extract flavours or to soften it. The specific process of teas being prepared for drinking by leaving the leaves in heated water to release the flavour a ...

germinating Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fern ...

and drying

grain A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...

to convert it into

malt Malt is germinated cereal grain that has been dried in a process known as " malting". The grain is made to germinate by soaking in water and is then halted from germinating further by drying with hot air. Malted grain is used to make beer, wh ...

. The malt is mainly used for

brewing Brewing is the production of beer by steeping a starch source (commonly cereal grains, the most popular of which is barley) in water and #Fermenting, fermenting the resulting sweet liquid with Yeast#Beer, yeast. It may be done in a brewery ...

whisky Whisky or whiskey is a type of distilled alcoholic beverage made from fermented grain mash. Various grains (which may be malted) are used for different varieties, including barley, corn, rye, and wheat. Whisky is typically aged in wooden c ...

making, but can also be used to make

malt vinegar Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting simple sugars to eth ...

malt extract Malt is germinated cereal grain that has been dried in a process known as "malting". The grain is made to germinate by soaking in water and is then halted from germinating further by drying with hot air. Malted grain is used to make beer, whis ...

. Various grains are used for malting, most often

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...

sorghum ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many othe ...

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

rye Rye (''Secale cereale'') is a grass grown extensively as a grain, a cover crop and a forage crop. It is a member of the wheat tribe (Triticeae) and is closely related to both wheat (''Triticum'') and barley (genus ''Hordeum''). Rye grain is u ...

. Several types of equipment can be used to produce the malt. Traditional floor malting germinates the grains in a thin layer on a solid floor, and the grain is manually raked and turned to keep the grains loose and aerated. In a modern

malt house A malt house, malt barn, or maltings, is a building where cereal grain is converted into malt by soaking it in water, allowing it to sprout and then drying it to stop further growth. The malt is used in brewing beer, whisky and in certain food ...

the process is more automated, and the grain is germinated on a floor that is slotted to allow air to be forced through the grain bed. Large mechanical turners, e.g.,

Saladin box A Saladin box is an instrument used for malting barley. It consists of a large rectangular container about 50 meters in length, and a set of vertical screws attached to a crossbar. The crossbar moves horizontally across the length of the container ...

es, keep the much thicker bed loose with higher productivity and better energy efficiency.

Intake

The grain is received at the

from the farmer. It is taken in from the field and cleaned (dressed), and dried if necessary, to ensure the grain remains in the best condition to produce good malt. It is tested to check for suitability for malting and to prevent dead or unfit grain from entering the process. Typical quality checks include: * Moisture content * Nitrogen content (total nitrogen) * Percentage of foreign matter * Absence of fungal growth and metabolites * Germinative capacity and germinative energy * Water sensitivity

Drying

Barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...

received at the malt house with moisture of more than 13% must be dried before it can be safely stored without loss of germinative capacity. The moisture is removed by circulating heated air (up to 50 °C) through the grain and can either be performed using dedicated grain driers or as a batch process using a

kiln A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay int ...

. High temperatures or over-drying will damage or kill the barley embryos and the grain will not germinate after steeping. The dry barley can safely be stored for up to 18 months without fungal growth or loss of grain vigour.

Cleaning

The aim of barley cleaning is to remove foreign matter (straw, chaff, dust and thin corns) found in the incoming grain, leaving only the grain most likely to produce a good malt.

Magnets A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...

are used to remove ferrous metals from the grain, in turn reducing the possibility of sparks, which could lead to a

dust explosion A dust explosion is the rapid combustion of fine particles suspended in the air within an enclosed location. Dust explosions can occur where any dispersed powdered combustible material is present in high-enough concentrations in the atmosphere or ...

. Rotating and shaking

sieves A sieve, fine mesh strainer, or sift, is a device for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet material. T ...

are used to remove unwanted foreign matter either larger (straw and un-threshed ears) or smaller (sand and thin corns) than the normal barley grain. During the sieving process an aspiration system removes the dust and

chaff Chaff (; ) is the dry, scaly protective casing of the seeds of cereal grains or similar fine, dry, scaly plant material (such as scaly parts of flowers or finely chopped straw). Chaff is indigestible by humans, but livestock can eat it. In agri ...

. De-stoners or shaking screens are used to separate small stones from the barley. The stones, which are denser than the barley, move out the top of the machine and the cleaned barley exits at the bottom. Half corn separators may be used to remove broken kernels. Half kernels need to be removed as only the one half will germinate and produce enzymes. At the end of the cleaning process the grain is weighed to determine the cleaning losses (the difference between the weight of grain received and the weight of the grain after cleaning) and it is transferred to a

silo A silo (from the Greek σιρός – ''siros'', "pit for holding grain") is a structure for storing bulk materials. Silos are used in agriculture to store fermented feed known as silage, not to be confused with a grain bin, which is used t ...

for storage.

Storage

The barley must be safely stored to maintain the grain vigour for germination. Storage at a malt house is normally in vertical silos made of steel or concrete for ease of use, but may be in flat stores when large amounts of grain is to be stored. The grain is stored in a manner that protects it from moisture and pests. A typical silo will store between 5,000 and 20,000 tons of clean dry barley ready for malting. During storage the temperature of the silo is measured and monitored over time as a temperature increase can indicate insect activity. Additional equipment may be used to keep the grain temperature below 18 °C to inhibit insect growth. Silos are normally fitted with a system for rotating grain from one silo to another to break-up hot spots within the grain. A

fumigation Fumigation is a method of pest control or the removal of harmful micro-organisms by completely filling an area with gaseous pesticides—or fumigants—to suffocate or poison the pests within. It is used to control pests in buildings (s ...

system can be used to administer a fumigant (normally

phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...

) to the silo.

Wet process

The wet process begins with steeping to get germination started and ends with

ing which removes the moisture and produces a stable final product. A batch of malt is known as a ''piece'' and a piece can be as large as 400 tons. Below a standardised base malt protocol is described:

Steeping

Steeping Steeping is the soaking of an organic solid, such as leaves, in a liquid (usually water) to extract flavours or to soften it. The specific process of teas being prepared for drinking by leaving the leaves in heated water to release the flavour a ...

is the start of the active malting process. Steep water is added to cover the grain and the grain moisture content increases from around 12% to between 40 and 45%. In a modern pneumatic malt house, the grain is alternatively submerged (wet stand) and then drained (an air rest) for two or three cycles to achieve the target grain moisture content and chit count. The first visible sign of germination is the appearance of rootlets known as "chit"; the proportion of chitted grains indicates the progress of the steeping process. When the grain is immersed in water (known as a "wet stand"), air is bubbled through the slurry of water and grain periodically. The aim of this aeration is to keep the process aerobic to maximize barley growth. Other advantages of the rousing are to get good mixing, to loosen dirt and to even out hydrostatic pressures at the bottom of the steep vessels. (Air flow rate: 1.5m³/ton per hour) At the end of the wet stand the water is drained out and this is the start of the "air stand" or "air rest". Fans are run to supply fresh air to replenish oxygen and to remove excess carbon dioxide produced by grain respiration. The temperature of the air supplied is important as the grain should be kept between 10 and 15 °C. The aeration requirements (cubic metres per ton per minute) are higher in the second and third air rests as the grain's metabolic activity is higher. (Air flow rate: 300m³/ton per hour). At the end of steeping the grain is "cast-out" to germination. Cast-out may be done as a slurry during a wet stand or as moist grain during an air rest.

Germination

The aim of

germination Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...

is to grow the barley grains. This allows the development of malt enzymes, and these enzymes modify the structure of the barley endosperm by breaking down the cell walls and the protein matrix. Germination produces a large amount of heat; if safety precautions are not taken the malt will burn. Grünmalz

The enzymes produced during germination are needed to break down the

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...

for the brewer or distiller during the mashing process. The grain bed is maintained at a constant temperature of between 10 and 16 °C by the constant supply of fresh humidified air. Turners move through the grain bed to keep it loose to allow for sufficient airflow.

Kilning

Kiln A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay int ...

ing reduces the grain moisture content and stops the germination process. In the first stage, the "free drying stage" the air temperatures are kept cool to dry the grain without causing the enzymes to denature. As the grain dries it is possible to raise the incoming air temperature for the second stage of forced drying to further dry the grain; the target malt moisture after kilning is around 5% by weight. During forced drying the relative humidity of the air coming from the bed drops, and the maltster is able to use a portion of the warm air as return air. During the last few hours of kilning the air temperature is raised to above 80 °C (the "curing stage") to break SMM down to DMS to reduce the DMS potential of the malt. DMS is an off flavour that tastes like sweetcorn in the final beer. The high temperatures of kilning also produce the colour in the malt through the

Maillard reaction The Maillard reaction ( ; ) is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor. Seared steaks, fried dumplings, cookies and other kinds of biscuits, breads, toasted marshmallows, and man ...

. Finally the kilned malt is cooled before the kiln is stripped (emptied).

Deculming

The rootlets of the malt (also known as culms) are removed from the malt soon after transfer from the kiln. The removed culms are sold or processed as animal feed. The cleaned malt is stored in silos to be blended with similar malt pieces to produce larger homogenous batches of malt.

Malt cleaning

Finally the malt is cleaned prior to sale using sieves and aspiration to remove the dust, lumps and stones in the malt. Magnets are used to remove any steel that might damage the mill rollers.

References

{{Authority control Brewing Malt