In order to explore the flavour produced by dark specialty malts, wort samples were brewed with different malts and evaluated by sensory and instrumental analysis. With increasing wort colour, a trained tasting panel detected more intense bitter and burnt flavours, whereas sweet and husky flavour notes decreased. Conversely, caramel and bread-like flavour attributes had a maximal intensity for the intermediate wort colours. Tasting of 20 EBC worts indicated that the flavour profile was significantly affected not only by malt level and malt colour but also by malt origin. Furthermore, the darkest caramel malt (480 EBC units) was found to contain most Maillard aldehydes as determined by the reaction with thiobarbituric acid. Similarly, other intermediate products of the Maillard reaction such as acetic acid, diacetyl and 2,3-pentanedione were found to arise in a higher concentration in dark caramel malts (220-480 EBC units) than in roasted malt (1200 EBC units). Dynamic headspace GC /MS further revealed that brewing with dark specialty malts considerably increased the level of 3-methylbutanal, its aldol condensation product (2-isopropyl-5-methyl-2-hexenal) and heterocyclic Maillard compounds. In contrast, dark malts drastically reduced the amount of hexanal in wort. By means of HPLC, it was established that only extreme roasting temperatures lead to the thermal degradation of ferulic acid to 4-vinylguaiacol in malt.

Dark specialty malts are important ingredients for the production of several beer styles. These malts not only impart colour, flavour and antioxidative activity to wort and beer, they also affect the course of wort fermentations and the production of flavouractive yeast metabolites. The application of considerable levels of dark malt was found to lower the attenuation, mainly as a result of lower levels of fermentable sugars and amino acids in dark wort samples. In fact, from the darkest caramel malts and from roasted malts, practically no fermentable material can be hydrolysed by pilsner malt enzymes during mashing. Compared to wort brewed with 50% pilsner malt and 50% dark caramel malt or roasted malt, wort brewed with 100% pilsner malt contained nearly twice as much fermentable sugars and amino acids. Reduced levels of yeast nutrients also lowered the fermentation rate, ranging from 1.7°P/day for the reference pilsner wort of 9 EBC to 1.1°P/day for the darkest wort (890 EBC units), brewed with 50% roasted malt. This additionally indicates that lower attenuation values for dark wort are partially due to the inhibitory effects of Maillard compounds on yeast metabolism. The application of dark caramel or roasted malts further led to elevated levels of the vicinal diketones diacetyl and 2,3-pentanedione. Only large levels of roasted malt gave rise to two significant diacetyl peaks during fermentation. The level of ethyl acetate in beer was inversely related to colour, whereas the level of isoamyl acetate appeared to be affected by the use of roasted malt. With large levels of this malt type, negligible isoamyl acetate was generated during fermentation.