Diacetyl control with biology

We have been receiving a lot of inquiries regarding our Acetolactate-Decarboxylase (ALDC) solution for accelerating/eliminating maturation process in brewhouses.   

Diacetyl and 2,3-pentanedione, also known as vicinal diketones (VDKs), are flavor components generated at the beginning of fermentation. If they exceed the specific threshold, VDKs will give beer an undesired off-flavor. Diacetyl, known for its butterscotch or buttery flavor, is the main contributor to these off-flavors. The presence of diacetyl is highly undesirable for most beers as it gives the beer a very unpleasant flavor, even in concentrations as low as 0.1-0.2 ppm. 

The reduction in VDKs, carried out by yeast during storage, goes hand-in-hand with other maturation processes and is considered an essential criterion for evaluating the degree of maturation of beer. However, the maturation time required to ensure that there is no diacetyl off-flavor varies considerably according to several factors, e.g. beer type, yeast strain, and fermentation and maturation temperatures.  

Maturation is the longest single stage in the production of beer. Acceleration/elimination of this stage would mean a shorter processing time and fewer tanks tied up maturing beer.  

Optimization in the maturation process depends on the yeast strain, the condition of the pitching yeast, the wort composition and gravity, the process management of the fermentation, and the size and shape of the fermentation vessels. Several approaches have been tested to accelerate/eliminate maturation step; 

  • introducing a warm rest at the end of primary fermentation 
  • the development of genetically modified yeast strains 
  • using immobilized yeast reactors 
  • using heat treatment under anaerobic conditions to encourage the direct non-oxidative decarboxylation of alpha-acetolactate to acetoin. 
  • addition of alpha-acetolactate decarboxylase (ALDC) to the pitching wort.  
  • During fermentation α-acetolactate decarboxylase directly transforms the precursor of diacetyl - α-acetolactate - into acetoin, and thereby reduces or eliminates the need for extended beer maturation.  
  • In order to maximize diacetyl prevention, it is important that ALDC be present in the wort at the same time with yeast. 

Novozymes Maturex® Pro is an Acetolactate-Decarboxylase (ALDC) prevents the formation of diacetyl and 2,3-pentanedion by converting precursors directly into the flavor-free end-products of acetoin and 2,3-pentanediol (Figure 1). This leads reduction in maturation time by 2-14 days depending on the brewing process.

Fig. 1. Action of Novozymes Maturex® during fermentation.  

A large-scale diacetyl rest trial with lagers showed that using a standard fermentation temperature profile with a diacetyl rest at 14.5°C, the addition of Maturex® results in achieving acceptable diacetyl values 4 days early—at day 7 instead of day 11, as demonstrated in Figure 2 and 3. In this case, the diacetyl rest was shortened from 4 to 2 days, thereby saving energy. 

Fig. 2. Reference fermentation with lagers. 

Fig. 3. Fermentation with the addition of Maturex® and reduced diacetyl rest with lagers. 

Beers made with or without Maturex(R) Pro are very similar in every respect apart from total processing time. After final filtration and packaging, standard beer analyses result in similar profiles from both chemical and sensory standpoints. Given the same short processing time with or without ALDC addition, the beers produced with Maturex(R) Pro all receive significantly higher taste scores than those produced without Maturex(R) Pro. Taste evaluation of the beers showed that the only significant influence of Maturex(R) Pro on the taste or the flavor was elimination of the diacetyl flavor. The higher flavor scores were mainly due to lower levels of off-flavors (described as diacetyl) and also, in some cases, to a heightened perception of freshness.  


About the Author

Dilek Austin, Ph.D.

Inside Sales Manager, Novozymes

Dilek is a lifelong food scientist with the specific focus on cereal science. For most of her career she has focused on cereal chemistry and baking. Beer is new to Dilek but certainly not a complete stranger; after all, beer is a liquid bread! Originally from Ankara, Turkey, Dilek has lived half of her life in US with her family. She enjoys gardening, crocheting, and learning new skills. While she drinks Witbier, her husband loves stouts. As usual, perfect Yin and Yang, opposite yet complementary!


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