The aim of the warm maturation process is to reduce flavour-active components such as diacetyl and, to a lesser
extent, 2,3-pentanedione. The presence of the diketones at levels higher than the flavour threshold is generally not acceptable in lager beer styles due to the butterscotch aroma.High levels of diacetyl at the completion of fermentation are
not limited to imbalances during fermentation performance. Other factors such as Pediococcus contaminations
(Sarcina sickness) and the presence of respiratory-deficient ‘petite mutants’ can contribute to increased diacetyl concentrations (Ernandes et al., 1993). Additionally, the initial valine concentration of wort (between 130 and 140 mg L1)
was found to contribute to the total diacetyl profile with longer transition phases and the second maxima that occurred later (Petersen et al., 2004). This resulted in extended diacetyl reduction times.