Adding darkness to your beer can be more than giving it a threatening image. Darkness typically means the use of roasted malts or barley in your grist and the subsequent development of coffee, chocolate and burnt flavours – in addition of course to a deep red or black hue.

Dark malts may comprise up to 10% of your grist – although at that level you would have a pretty harsh mouthful to manage. However, even 0.5% can provide benefits beyond a touch of colour.

Besides providing colour and major flavour components to milds, brown ales, porters and stout’s dark malts greatly assist stability in beers. This stability is particularly related to dark malts releasing compounds able to distract reactive oxygen species (ROS) from oxidising and staling beer. Their action is to bind the high energy ROS and prevent them reacting with more sensitive beer compounds to produce undesirable and stale flavours, haze and harsh characteristics.

Not that a good brewer will have excess oxygen present in their worts or beers but a certain level is inevitable as we can’t brew in a vacuum – or in most cases under a protective blanket of inert gas.

Even low levels of oxygen can be energised to ROS by the presence of certain metal ions such as copper or iron or by enzymes or, in unusual cases, by light. Foaming transfers of worts and beers, leaking transfer lines, vessel corrosion or lack of a carbon dioxide blanket will all enhance oxygen and ROS levels.

Dark malts can be a saviour to this as their antioxidants are available to mop up the oxygen present without affecting flavour. Estimates suggest that malts can contribute 95% of the antioxidants in dark beers and 86% in light beers. In addition they can reduce haze development arising from the precipitation of polyphenols which are also accelerated in the presence of oxygen. At a more basic level dark malts do make it more difficult to see haze in a beer – although a determined customer with a pocket torch may make a more informed assessment.

The exact antioxidants in malt responsible for their protective action vary according to the barley variety, the malting process and the roasting conditions.

One of the major browning processes is the Maillard reaction whereby sugars react with amino acids and produce a wide range of small and large compounds with varying antioxidant ability – as well as colour and flavour. However, these may be only a part of the full range of
antioxidants and others are already present in barley or are produced in mashing so explaining why beers differ in how easily they stale. To obtain consistency it may be necessary to keep to the same ingredients and processing and not vary your sources of dark malts.

Light beers are obviously at greater risk from reactive oxygen but small proportions of dark malts may provide some protection without greatly affecting flavour or colour – perhaps as low as 0.5%. In addition analysis has indicated that antioxidant production in dark malts may be separate from colour development.

This suggests that it may be possible to obtain malts with high levels of antioxidants but limited colour. In reverse, however, it also suggests that not all coloured malts will be antioxidant or protective. Malt colour extracts may be particularly lacking. Maltsters may in the future be able to specify the level of antioxidants in your choice of malts so allowing you to balance colour and stability.

Moreover, dark malts can, in some conditions, release oxygen into beer. For this it is necessary for the malts to be saturated with oxygen, perhaps through very poor processing, and then pass this on to beer components. Beer processing can also destabilize beer – fine filtration for example can remove some larger antioxidants suggesting that unfiltered or bottle conditioned beer may have an enhanced shelf life. Enhanced head retention may also be evident.

Of course malt isn’t the only protective ingredient in your beer. Yeast will readily remove oxygen and can be a major factor in the stability of cask and bottle conditioned beer. Keeping your yeast active before casking and bottling will also enhance your malt antioxidant action.
Hops are a further influence and recent work has shown that αacids are particularly protective. Since αacids are converted to iso αacids during boiling it has been suggested that a progressive addition of hops during boil and in dry hopping is more protective as there will be a greater proportion of αacids present throughout processing.

The final value of dark malts to beer is their versatility in broadening your recipe range. Roasting temperature makes a large difference to flavour and colour production aside from antioxidants and careful choice can provide a wealth of novelty. Black IPA may be just the beginning.


Written by Dr Keith Thomas
Brewlab Director

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