Once the malt has achieved the anticipated degree of modification, it is kilned, this is a monitored heating process which extracts moisture, preventing further development and stabilizing the malt for long-term storage.
The addition of colour and aromatic flavours during kilning is known as browning. Each time you put a slice of bread into the toaster, you’re doing the same thing. Applying heat to starchy or sugary food results in colour and flavours to develop. It sure would be a very boring world without this process.
There are two common types of browning: caramelisation and Maillard browning. Both require the conversion of carbohydrates, using heat, into colour and aroma composites. They are different due to the presence or absence of nitrogen; caramelisation doesn’t use it, but Maillard browning utilises nitrogen. Each has its own character, but in both, heat triggers chemical reactions which convert sugars into two separate sets products: melanoidins and small molecules known as heterocyclics.
Melanoidins are big, polymeric molecules with slight aroma and differing levels of bitterness, which may be essential to consider in a recipe. They provide beer with its wonderful colour. Science hasn’t yet understood detailed chemistry which surrounds them, but it is accepted that lightly kilned malts yield more yellowish colours, whilst caramel and black malts regularly appear reddish, an vital detail if you’re trying to brew an amber ale.
Melanoidins are also vital for redox reactions; this is the chemistry of oxidation, central in beer aging and flavour stability. Dark malts can act as oxidation scavengers, giving away electrons to oxidizers in one process of the brewing process, this is beneficial, but under certain situations, releasing them, which is bad. Dark beers are in less danger of oxidised flavours during aging, but melanoidins formed in paler beer, by, for example, direct-fired boiling, can provide issues. Malt aroma is provided by heterocyclic, or ring-shaped, molecules carrying one or more “foreign” atoms such as oxygen, nitrogen, or sulphur on their ring. They have fiery names such as pyrrholes, pyrazines, furanones, and are remarkably strong aromatics; plenty have onsets in the parts-per-trillion range. There are hundreds of different varieties in malt and beer, and they generate the full spectrum of malt aromatics.
Small differences in the browning process form very different malt flavours. Moreover, every different arrangement of carbohydrate, nitrogen, time, temperature, pH, and moisture level will yield different end products; keep this in mind when choosing malts for your brew recipe.
There are lots of different ways to assemble a beer of a particular colour; this means that two beers with identical colours can have considerably different flavours. A minor amount of a dark malt will create a radically different beer than one brewed with a higher amount of lighter malt. Even different malts of the same colour can have hugely different aromas, produced by different moisture levels or temperatures during kilning. While colour is very important, it is also vital to get the flavour for the particular style or recipe.
The majority of malt flavour and aroma derives from Maillard browning; however there are some malt varieties where non-Maillard caramelisation dominates. With caramel malts, a large amount of malt starch has previously been transformed into sugars; this is shown by the glassy crunch. Instead of the usual malt aromas of bread and roasty sensations, the aromas of caramel malt range from sweet caramel to toasted marshmallow all the way to burnt sugar.
Two pieces of equipment are used by maltsters to dry and colour malt: a kiln and a roaster. Kilns do the majority of the work; they utilise a lot of air movement and a lower range of temperatures. They extract moisture and, as moisture levels decrease and temperature rises, they start to add colour to the malt.
Maillard Browning vs Non-Maillard Caramelization
Malt Colour Wheel
When viewing the above image, keep the following things in mind:
- Typical kilned and roasted malts around the outside
- Outermost malts kilned moist for caramel flavours
- Next inner types kilned dry for toasty flavours
- The gap represents a harsh, ashy zone; no malt is made in this colour range
- Inner ring is caramel malt types.
- Red signifies the reddest shades of malt
- The malt colour wheel classifies different types of malts by the temperature at which they are kilned and the colour that they create.