Glycosidic Nitrile, You Really Should Care Now 

person holding grains

By: Becky Garrison

At the American Craft Spirits Association’s 2022 conference held February 10-12, 2023, in Portland, Oregon, Dr. Campbell Morrissy, a graduate research assistant in the Barley Project at Oregon State University, led a talk about why distillers should be concerned about Glycosidic Nitrile (GN).

  First, he defined GN as “naturally occurring plant metabolites that are used as defenses against predators.” They’re actually pretty sweet, and they are present in almost all plants.” Epiheterodendrin (EPH) is a type of GN found naturally in barley. 

During fermentation, yeast contributes beta-glucosidase, which acts on EPH, resulting in a precursor to hydrogen cyanide. Add heat and copper, and then suddenly,  EC (ethyl carbamate) is present in the final spirit.

    In the United States, there’s a voluntary limit of 125 parts per billion of EC permitted in alcohol products available for sale, which is quite low. As this is a voluntary limit, it’s become a regulatory gray area. As far back as 1993, high enough levels of EC were found in bourbon produced in the United States that would have exceeded regulatory limits established by the EU, UK, Canada and some other countries. Additionally, whiskey sold in Europe needs to meet that low EC concentration. So, those selling to the EU market may face regulation and monitoring of EC levels.

  About 30 years ago, those working with barley in the UK began to realize that GN resulted from barley variety. Now, more than 50 percent of all malting barley purchases in the UK are GN zero and essentially all for the distilling market. Morrissy added that those making whiskey in the UK use GN zero malt with no exceptions.

Defining Barley Varieties and EC Levels

  Generally, there are three categories for defining barley varieties and their propensity to create EC. The non-producer is GN zero, defined as anything less than half a gram per ton of EC. Low producers have 0.5 to 1.5 per ton, and high producers are 1.5 or greater per ton.

  A barley’s ability to produce EC can be measured in two ways. A PCR assay can ascertain whether a given barley variety will have the gene to produce EPH. Also, the quantitative method enables one to measure photometrically if a particular barley reacts to hydrogen cyanide.

  Low GN producers will still produce GN, and its production can be modulated during malting. Anything that’s going to promote malt modification is going to result in more GN. Here, one needs to look at the length of germination. Typically, the germination time for brewing malt is about four days, though with a distiller’s malt, germination can go up to five days, depending on the type. As germination increases, one can see a pretty clear relationship with the level of glycosidic nitrile. While barley variety is important, what matters more is how it malts. Hence, Morrissy recommends connecting with the malthouse to work together to see if pushing modification will impact the EC levels of the resulting spirit.

What Look for When Breeding Barley

  First and foremost, Morrissy stresses looking for strong agronomics. “The farmers are going to need to grow something that they can rely on. Thankfully through very traditional plant breeding techniques, we produce high yielders with low disease resistance, which means fewer inputs. We breed for intolerance for drought and look into low-temperature tolerance for winter lines,” he states.

  Also, Morrissy suggests looking at AMBA-recommended specifications for malt guidelines to select grains known to produce high-quality malt. Along those lines, look for multi-environment adaptation that can be grown all over the place and weather new climatic experiences.

  Here, one needs to differentiate between growing spring or winter barley. Spring barley is planted in the spring and harvested in the summer. Conversely, winter barley is planted in the fall and harvested in the summer. Unlike spring barley, winter barley goes through vernalization and overwinters.

  Winter barley yields more often and has a low-temperature tolerance and less water requirement. When it requires water, it tends to be when water is abundant in most regions due to runoff from winter and late spring rains. While one of the best things for winter barley is snow, some historically very cold places do not see the same snowpack they used to see. Also, winter barley is an excellent erosion control for winter.

  Morrissy observes, “In those places that are windy, putting something that has a root structure in the ground can preserve a lot more topsoil. You also kind of have a de facto cover crop in a time that it might be fallow, so you’re going to out-compete weeds. You may have some pest resistance associated with that.”

  Morrissy notes that different regulatory mechanisms within that GN gene pack can turn on or off depending on climatic changes. Right now, they are not sure how environmental stress response impacts GM production. Currently, more research is needed to understand how the environment impacts GM production in the field.

Producing GN Zero Barley Varieties

  Currently, there’s one GN0 variety approved by the American Malted Barley Association (AMBA). However, Morrissy predicts that with the advent of AMBA’s new recommendations that all varieties of malt for distilling be GN zero, we will start seeing more of these come on the market for brewing and distilling as they go through the AMBA pipeline. Also, some foreign varieties are coming from the private breeding program, and U.S. land grant institutions are breeding some domestic varieties.

  An interesting alternative is naked or hull-less barley. Inherently naked barley is GN zero, though, as Morrissy noted, there isn’t a great supply chain for naked barley right now. Still, there’s a lot of potential for sowing grain without the husk, as that can take up five to seven percent of the total weight of the grain. “If you’re not lautering, you’re doing grain fermentations, or maybe you have a mash filter, you don’t need the husk,” he states.

  At this writing, 10 public breeding programs in the US are working on barley. They’re covering many different areas, producing barley that’s well suited for those larger growing regions and collaborating to make sure that the genetic stocks for sustainability are being shared industry-wide.

Managing EC in the Distillery

  EC is a lowly volatile, heavyweight compound,   whereas its precursor hydrogen cyanide is a very highly volatile, low molecular weight compound. So, according to Morrissy, the more EC that can be formed in the stills and recovered in the silage, the less it will make it into the barrel. Depending on the distilling technique, Morrissy thinks the cyanide fraction is volatile, and the conversation into EC happens very quickly, though it might not get picked up until the spirit is in the barrel.

  Early investigations into the distilling technique find that reflux is highly important in controlling EC. Also, still design and still feed are so important. Trace amounts of EC will form during fermentation, but primarily, the copper catalyst in distillation produces EC. While this work is in the emerging stages, research with copper contact and reflux and controlling EC looks promising.

  For further research into this topic, Morrissy recommends The Hartwick College Center for Craft Food & Beverage, a testing and education resource that supports small and mid-sized breweries, malthouses, farms and other craft food and beverage producers. Also, he suggests joining the American Malted Barley Association.

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2 thoughts to “Glycosidic Nitrile, You Really Should Care Now ”

    1. The use of malt with high GN content in distilling can produce significant levels of ethyl carbamate (EC) which is a potential carcinogen and regulated in some markets (Canada & EU).

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