Staling is the general term we use for undesirable flavors that occur during the aging of beer. Why should a homebrewer care? You may respond with, “My beer never gets old enough to stale.” Or, “I never brew light beers and I have not noticed this.” Or, “I never let beer out of my control.” While there may be some merit to this, this column is geared to highlight a new pedigree of barley that has been shown to not only help limit certain staling effects, but also increase head retention in beer brewed with it.
Staling is of both quality and economic importance. Most, if not all, large breweries invest considerable resources into improving the shelf life of beer. The R&D program at Sierra Nevada has always maintained a strong focus on increasing the quality of both their fresh and their aged beers for example. It is very challenging for a brewer to release beer into the wild and lose control of its storage conditions and serving date. Brewers have approached the problem from many directions, making beers that last longer, educating distributors on how to keep beers fresh and educating consumers on the importance of fresh beer. Despite all these efforts, it is still common to find stale beer in the trade. As a homebrewer, if you want to enter a competition, the beer will be out of your control. In fact shipping beer is likely to accelerate the staling process. Also, it is common for homebrewers to give beer as gifts. You wouldn’t want your gift to go stale before it was appreciated. Or perhaps you want to make a beer specifically to age.
Let’s start with considering how artificial staling is done. The two common methods are to store the beer warm or alternate warm and cold cycles. Sierra Nevada claims to be able to replicate 3 months of staling time in 7 days in its artificial aging chamber. Once a beer is brewed its quality will change over time. Some qualities can improve while others degrade. The malt, hops, and yeast character can change dramatically over timeframes as short as a few weeks. Oxygen is particularly harmful to beer and steps are taken at most breweries to lower the oxygen uptake at all phases of beer production with the exception of right after wort is cooled and yeast is added. But even at this phase of the process; there are brewers who have found novel ways to lower oxygen during wort aeration as well. Here we will describe one of the ways oxygen contributes to the most common staling flavor; wet paper.
Among the most studied beer staling molecules in pale lagers is trans-2-nonenal (T2N). It has the aroma/flavor that is often perceived as wet paper or wet cardboard. If this flavor is not familiar to you, there are spiking kits available to simulate this flavor or you can wrap a beer in a wet paper bag and drink it. Another way, albeit slow, is to take a light flavor beer and leave it warm for 6 months.
T2N has a flavor threshold of 100 parts per trillion making its control very important. To put that number into perspective, one gram of T2N will render over 26 million gallons of beer stale tasting! While this is not the only factor we need to worry about during aging, we will focus this issue’s column to T2N and its sources. Because this flavor is so dominate in the staling of pale lager beers we don’t have much data on it for big craft beers. I propose that the large hop additions currently in vogue supply reductones to help limit this reaction and as the market returns to balance craft brewers too will have to consider this important molecule.
T2N is formed as the degradation product of poly-unsaturated fatty acids oxygenated by the lipoxygenase (LOX) enzyme. Let’s slow that last sentence down and pick it apart so everyone can understand. Fatty acids are oxygenated in a catalytic reaction by the LOX enzyme to form a conjugated hydroperoxide. Once this reaction is complete the LOX is unchanged and free to catalyze another fatty acid. This hydroperoxide product is subsequently degraded later in the process but most importantly in the package into T2N.
LOX-enzymes are created while the plant is growing. During malting, the germination step activates the LOX enzymes causing them to create T2N. Since enzymes work more quickly as they warm up, as long as not denatured by extreme heat, lowering germination temperatures are effective in lowering LOX activity. LOX is denatured at low heats and kilning malt at a higher temperature and/or a longer time will denature most of the LOX at the expense of making slightly darker base malt. If LOX survives malting it will be activated further in the mash. LOX enzymes are almost entirely denatured by the boil. In addition hydroperoxides and T2N created before boil will be volatized in the boil.
For the last 60 years there has been a steady decline in the levels of LOX in malting barleys. It is likely that selective breeding for flavor has worked to lower this problematic enzyme. LOX comes in two varieties named LOX-1 and LOX-2. LOX-1 is been shown to be the most important pathway to T2N. Gamma-nonalactone is also formed from lipid degradation and has been shown to increase the degree of staling flavor when combined with T2N. It should be noted there is also a non-oxidative pathway to T2N formation from a nitrogenous (Schiff) base that is activated in boil and continues into the finished beer. Research is divided as to the importance of these two paths but the available research into LOX shows a reduction in T2N levels in the packaged beer.
While LOX is very thermolabile (is easily destroyed by heat) and is largely destroyed during mashout and completely destroyed by boil, the conversion to hydroperoxide has already been done. Brewers can further reduce the LOX activity by increasing boil evaporation to remove the hydroperoxide precursor and by decreasing the pH of wort. Homebrewers already have a fairly high boil-off rate compared to professional brewers, so homebrewers have had an advantage there. Since LOX requires oxygen to make T2N it is logical to assume that lowering oxygen or increasing reductones would help to lower T2N levels in finished beer. Lowering hot-side aeration is also beneficial in limiting oxidized fatty acids. Not only do the LOX enzymes create the T2N molecule but LOX also seems to play a part in the production of trihydroxyoctadecenoic acid (THOD). THOD has been implicated in the staling process and is also a known foam-negative compound.
Remove the LOX
LOX-less (also called Zero-LOX or LOX-Null) barley lacks the LOX enzymes that create the T2N compound. So let’s delve into the genetics of LOX-less barley. LOX-1-less barley was first bred from an existing recessive gene collected by the Institute of Plant Sciences and Resources, Okayama University, Japan from an Indian landrace (pre-hybridized) barley (OUI003, Code Number SBOU2) crossed with Canadian CDC Kendall with marker assisted backcrossing in 2001. This barley was named CDC PolarStar. PolarStar was the first commercial barley variety to eliminate LOX from the barley grain, this work was repeated by University of Adelaide using the Australian malting barley variety Flagship. Both programs were sponsored by Sapporo Breweries Ltd, Japan. Carlsberg and Heineken also bred barley without Lox-1 (2001) and later entirely without LOX-1 and LOX-2 (LOX-less) (2010). Interestingly six LOX-less landrace barleys have been identified and further work in producing LOX-less barley specifically bred for brewing purposes is underway. There are now many LOX-less varieties available to both the pro and homebrewers (see Chart 1 below).
These new barley varieties have performed well in the field, malt-house, lab testing, small and large-scale trials and are in use in some of the largest breweries in the world. For the farmer, the yield per acre, time to maturity, kernel size, and kernel qualities match standard varieties. For the brewer, the levels of extract, nitrogen (FAN levels), beta glucans and diastatic power are within normal brewing ranges. A big surprise in this research has been the low levels of THOD in LOX-less variety produced beers. It is not known if the varieties are genetically predisposed to have lower THOD or if the LOX enzyme participates in some way to the formation of THOD. Further barley lines are being developed specifically to explore the effect breeding can have on foam retention.
Why go through all of this effort? Lab analysis has shown a marked decrease in T2N levels in aged beers and much longer head retention for beers brewed with these malts. In fact the LOX-less barley produces 1⁄50 th the T2N compound and 1⁄2 to 1⁄3 of the THOD after storage. As a result, the beers have longer shelf life and a much improved head retention thanks to the reduction in these two compounds (see Charts 2 and 3 below). In fact, there was up to 30 minutes improvement in head retention found in some trials.
There seem to be no drawbacks in other aspects of the resulting beer. In a blind analysis by “very experienced” tasters it has been shown that the stale and papery quality of fresh beers is much lower than control varieties and both forced- and natural-aging studies have shown the T2N levels are lower in beers produced with LOX-less varieties. Qualitatively, these aged beers show a much better score for staling qualities with the LOX-less varieties. So far there are no studies on three-year-old beers to show if there is a benefit in LOX-less varieties but the shorter-term results seem to point towards positive long-term benefits. Also, the levels of Gamma-nonalactone, the synergistic staling compound with T2N, have been lower in Lox-less variety based beers.
Notable in the data from Hirota (Chart 2) is that even with LOX-less varieties the T2N is not zero. Although the numbers are lower and have been repeated by other researchers. This leads one to consider other sources of T2N and that research is continuing. Some pathways have been proposed, and look promising, but, so far, no one has published a specific pathway.
I was able to run several sensory trials on grains and worts as well as batches of beer brewed on homebrew-sized equipment and have found that the flavors and brewhouse performance is equivalent to more traditional brewing varieties. These tests, which included side-by-side trials with many of the popular homebrewing base malts showed that the fresh beer was very similar to traditional malts. (The LOX-less Viking Pale Zero and Pilsner Zero malts were used for these trials.)
Staling is a common problem in beer. Brewing researchers have identified many flavors that are caused by aging that are detrimental to beer. LOX-less barley has given brewers a new tool in controlling staling, specifically by the T2N pathway catalyzed by the LOX enzyme. Its brewhouse performance and cost is unchanged from traditional varieties and is another weapon in a brewer’s arsenal.
Mash a liter and give the wort a taste to see how those compare to similar grains. If you like it, give it a brew! You may find it is the base grain that you use for beers that may sit in your kegerator or bottle longer than others.
T. Hoki, W. Saito, N. Hirota, M. Shirai, K. Takoi, S. Yoshida, M. Shimase, T. Saito, T. Takaoka, M. Kihara and S. Yamada (2013). Breeding of Lipoxygenase-1-less Malting Barley Variety CDC PolarStar and Effect of Lipoxygenase-1-less Trait on Beer Quality at Pilot and Commercial Scale Brewing. Brewing Science, 66 (2). 37–45.
Hongxia Ye, Stefan Harasymow, Xiao-Qi Zhang, Blakely Paynter, Dianxing Wu, Michael Jones, Xiaoli Shu and Chengdao Li (2014). Sequence variation and haplotypes of lipoxygenase gene LOX-1 in the Australian barley varieties. BMC Genetics, 19. 15–36.
Junhong Yu, Shuxia Huang, Jianjun Dong, Wei Fan, Shuli Huang, Jia Liu,Zongming Chang, Yuhong Tian, Junguang Hao and Shumin Hu (2014). The inﬂuence of LOX-less barley malt on the ﬂavour stability of wort and beer. Journal of the Institute of Brewing, 120. 93–98.
Hirota, N & Kuroda, H & Takoi, Kiyoshi & Kaneko, T & Kaneda, Hirotaka & Yoshida, I & Takashio, M & Ito, K & Takeda, K (2006). Brewing Performance of Malted Lipoxygenase1 Null Barley and Effect on the Flavor Stability of Beer. Cereal Chemistry, 83 (3). 250–254.
Masaaki Yano, Masatoshi Morikawa, Tetsuji Yasui, Yutaka Ogawa, and Motoo Ohkochi (2004). Influence of Wort Boiling and Wort Clarification Conditions on Cardboard Flavor in Beer. MBAA Communicator Technical Quarterly, 41 (3). 317–320.