Lesson 6 - Speciality Malt and Adjuncts Final SAQ

*** How does the chemical composition of adjuncts and speciality malt affect beer flavour and flavour stability?

Both adjuncts and speciality malt are used to influence beer flavour. The compounds responsible for their reported effects have not been established in all cases. Rather than trying to explain each effect, a more practical way to address this question is to take each component in turn and discuss its effects on flavour.

Non starch polysaccharides

Oats, raw/flaked barley, wheat and rye are significant contributors of non-starch polysaccharides. Raw barley and oats are high in β-glucans and wheat and rye are more well known for providing pentosans. Raw/flaked barley is also high in pentosans. Chit and short grown malt are part way between raw barley and base malt so are typically higher than malt in both β-glucans and pentosans. Some brewers feel that oats provide a smooth mouthfeel and this is attributed to β-glucans. Interestingly raw and flaked barley is not associated with a smooth mouthfeel and yet provides just as much. Rye is reported to have a spicy flavour and increase the complexity of mouthfeel. Whether either are due to pentosans is impossible to prove definitively, because you can’t measure spicy flavour and mouthfeel complexity in beer. Non starch polysaccharides are not thought to be significant to flavour stability.

Lipids

Some adjuncts in their unprocessed form contain a lot of lipids. Most products sold as adjuncts have usually been processed to remove parts of the grain high in lipids. Maize is infamous as a source of lipids but grits and flakes are usually lower than in lipids than malted barley. The solubility of lipids is as important as the total amount, as most do not dissolve in wort and are easily lost on spent grains and trub. Oxidised lipids are more likely to dissolve. Some breweries that use rice grits feel that if the grains are polished more than two weeks before use, fatty acids on the surface oxidise which can lead to rancid off-flavour in the beer. The whole grains are milled before use in the brewhouse. Lipid oxidation is one of the main routes of stale beer flavour formation. E-2-nonenal is formed from oxidised linoleic acid. Avoiding adjuncts that are high in soluble lipids is thus important if you want to keep beer as fresh as possible over its shelf life. That said, we do not want to go too low because yeast need fatty acids for cell growth and if our wort does not contain enough poor fermentations and hence poor beer flavour may result. This can be from H₂S, SO_2­ and organic acids, or from lack of attenuation and pH drop.

Protein

Protein is both directly and indirectly important for beer flavour. Protein and other larger nitrogenous material like large polypeptides are thought to contribute to the fullness of mouthfeel. How full tasting a beer should be, depends on the beer in question, so we must select the appropriate adjuncts for the beer flavour we require. Most adjuncts are lower in protein than malt so may reduce body. FAN, like lipids is required for yeast growth, so limiting the amount of FAN may cause similar problems along with excessive diacetyl levels. The use of adjuncts that dilute nitrogenous material has been found to increase flavour stability. Whether this is due to reduced nitrogenous material levels or just the dilution, of other stale beer flavour compounds from malt has not been established.

Non fermentable material

Some starch derived syrups can provide non fermentable material if their hydrolysis is less complete. The dextrins that they provide are thought by some to improve fullness and sweetness although there is conflicting evidence. Speciality malts that have been stewed then kilned or roasted can also provide unfermentable material. This is carbohydrate material that has been rendered resistant to hydrolysis as a result of the heat applied. Caramel and crystal malts are renowned for their ability to provide beer with a fuller and sweeter palate.

Non enzymatic browning products

Pyrolysis, caramelisation and most importantly the Maillard reaction provide speciality malts and coloured sugar products and beers brewed from them with their characteristic flavours. Maillard reaction products have been found to provide the following flavours: bready, biscuity, sweet, caramel, toffee, jam/conserve, candyfloss/cotton candy, molasses, fruity and roasty. The same can be said for caramelisation, apart perhaps for bready and biscuity, but caramelisation is unlikely to contribute to most speciality malts’ flavour. Pyrolysis provides burnt flavours like coffee, chocolate and roast and is only significant in highly roasted products. Maillard products like reductones and melanoidins are known as oxygen scavengers so some feel they improve flavour stability. However, recent scientific work has cast doubt on their long term effectiveness at preventing oxidation throughout shelf life. It seems that at some stage they change from antioxidants to prooxidants. Also, some of the heat derived flavour compounds found in highly coloured malts have been shown to play a part in stale beer flavour. This is either as stale flavour compounds or their precursors. Any ingredient that has been subject to high thermal load seems likely to reduce flavour stability.