If you want to get on top of beer stability, you’d be well advised to pay attention to light stability. The path leads via flavor. Light and flavor stability are research fields in brewing science that researchers have been digging into for a century. That means we know a lot about beer stability.
Beer aging manifests itself primarily in the flavor – in a change of bitter intensity, loss of bitter quality, increase in sweetness intensity, and the formation of typical stale
aromas often described as sticky, berry-like, or caramelly. This applies in particular to light, bottom-fermented beers, which have been intensively researched in this regard.
A number of carbonyls have been found to cause the stale flavor. Carbonyls are the product of various reactions such as oxidation, Strecker degradation, aldol condensation, or hydrolysis. They are characterized by one carbon atom and one double-bound oxygen atom, and they are very volatile and reactive. Carbonyl formation is promoted, among other things, by hops which provide additional material – and they do so with the aid of light. Light causes the cleavage of the side chain of the isohumulones which then react with the carbonyls, thus increasing the complexity of the aging substances. However, this also leads to the formation of the primary materials for entirely new, fruity aromas.
The light-sensitive bitter acids are therefore a further key factor in beer stability management. To prevent them from degrading, brewers have two options: Those working within the framework of the Purity Law protect the beer from exposure to light as far as possible. Outside Germany, they have the option of using “light-stable” hop extracts. To produce light-stable hop extracts, the alpha acids are first isomerized and then additionally hydrogenated. This allows a variety of stable bitter acids to be produced. The best known of these are the tetrahydroiso-alpha acids which are widely used for foam stabilization. However, there are also rho iso-alpha acids which are used specifically to achieve a pleasant and light-stable bitter flavor. Thanks to the stabilized bitter acids, certain offaromas, such as “lightstruck” flavor (3-MBT), cannot form at all and the bitterness remains stable longer. This is particularly important for beers that are bottled in green glass.
As a rule, these hop products are added to the finished beer prior to filtration. The addition of hops during the boil makes for a rounder flavor with regard to bitterness and is more practical for the brewer. Up until now, this was not an option for the lightstable bitter acids, as the actual bittering utilization would have been too low. However, this factor has been significantly improved in a new light-stable hop product. This year, BarthHaas is launching the hop extract Kettle Redi®, a rho-iso-alpha acid extract that is intended for use during the boil and boasts a rho-iso-alpha acid content of approx. 40 percent. If light stability is what you’re going for, you should note when using these products that solely light-stable hop products like Kettle Redi® or light-stable aroma products such as PHA® may be used. Even small quantities of “normal” iso-alpha acids will ruin the effect. If your focus is on the pleasant, smooth bitterness you get from Kettle Redi®, you can combine it with any other products. As the rho-iso-alpha acids in the extract are a finished product, the extract does not have to be boiled and can therefore be added at a later stage toward the end of the boil.
With regard to beer stability management as a whole, however, you have to be clear about one thing: Even though the bitterness is more stable due to the use of these extracts, that still leaves a lot of instability potential in the beer. The bitter acids may be out of the game, but all the other players can simply start a new one. Rather like in real life.
