Genetically Modified Yeast That Produce Hop Flavors – Does This Matter To You?

Genetically Modified Yeast That Produce Hop Flavors – Does This Matter To You?

by Mark E. Lasbury for Indiana On Tap

There are four main ingredients in beer – water, hops, malted grain, and yeast, and each plays a crucial role in the final product. However, while they are understood by casual drinkers to play a role, that role might be a bit mysterious or even misunderstood. As an example, water is the main ingredient in beer, but it’s really the minerals ions in the water that affect beer. People can spend years just learning about the role of water in beer.

Likewise, malted barley is present for the sugars that the yeast will consume, but it’s the enzymes in malted grains that render the sugars digestable. Hops may be the most well understood of the four main ingredients of beer; hops provide aroma and flavor molecules, are a bittering agent when boiled, and are antibacterial – many people nowadays know the story of the birth of the IPA.

On the other hand, yeast may be the most mysterious of four parts of the main constituents of making beer. Most people know that yeast digest some types of sugars to produce CO2 and alcohol, but that’s just where the story starts. Only a few styles of beer have many intact yeast cells in the poured product (wit beers and hefeweziens), but all beers have many yeast products in them. Yeast comes in different strains, and each contributes different metabolic compounds to the beer, and the concentrations and chemical formulations of these depend on both the strain and the fermentation conditions.

traditionally, beer is made of four ingredients. photo credit: LaserShark Brewing

In all, over 500 chemicals have identified that come from yeast or yeast breakdown products and work to mold the final beer flavor and aroma. If this weren’t the case, then all beer would taste like carbonated, alcohol-containing wort. There are yeasts that let the malt dominate, yeasts that make more fruity esters, yeasts that even let the water profile shine. The problem is, understanding yeast biology is more complex than the other components of beer. Understanding the yeast is what makes brewers scientists; understanding hops, barley and water is what makes them artists.

Beer can’t be made without yeast or water, although some styles can be made without one of the other main ingredients. Gruits are alternatively bittered beers made with heather or other herbs in place of hops. Some beers can be brewed with grain bills that don’t include malted barley, like The Unlauterable at Wabash Brewing or the Wheat Walker at Evil Czech Brewery. There are even beers that are made with human urine, but of course, that’s mostly water (OK, they used the urine to fertilize the barley, but still).

Now science is getting into the act when it comes to hops and yeast. Dr. Charles Denby’s group at UC Berkeley has been engineering yeast to produce plant terpenes as a source of sustainable fuels by introducing the plant genes (for terpenes) into the chromosomes of the yeast. Terpenes are compounds from plants and some insects that have a variety of shapes, sizes, and functions based on their number of isoprene units and the functional groups bonded to those units. With respect to beer, different terpenes provide flavors, but they are volatile and are lost to the air as the temperature of the wort increases. The alpha acids from hops that are converted to the bitter iso-alpha acids of beer when wort + hops are boiled are examples of terpenoids (compounds derived from terpenes). Dr. Denby is also an avid home brewer, and the idea of flavoring terpenes coming from yeast was not lost on him.

So, might it be possible to modify some yeast to produce terpenes that could add a dry-hopped flavor to beer? The results of his research say yes, as published recently in the scientific journal Nature Communications. Denby’s group transfected mint and basil terpene production enzymes (linalool and geraniol) into an ale yeast strain and he made beer with it to mimic a Cascade dry hopped beer. There were many experiments along the way, especially ones geared to controlling the rate of production of the terpenes by the yeast and working out how to ensure that the new products didn’t alter the performance of the yeast in its normal functions. But once everything was worked out, Denby thought he was on to something.

Hop alpha acids are types of derived terpene called terpenoids, but this still doesn’t account for the isomerization of the terpenoids during the boil. image credit: Natures Medicines

He took his beer to Lagunitas and had it blind taste tasted by forty people who know their beer. The majority of the sensory trained volunteers stated that the engineered beer actually had hoppier aroma than traditionally brewed beers. It may seem to be only a gimmick to many, but this idea might have long range effects on the sustainability of the craft beer industry.

Hops are expensive, in short supply, and intensive in the use of natural resources for their production. A genetically modified (GM) product that reduced brewers’ reliance on hops could save money and be good for the environment. However, by my reading of the journal article, GM yeast with terpenes (or even other flavor compounds down the road) won’t replace hops in beer. One of hops main jobs in the boil is to provide terpenoids that are converted to iso-alpha acids, the main bittering agents in beer. Boiling the terpene producing yeast to make iso-alpha acids would just kill these single celled organisms and not allow for production of alpha acids that could then be converted to iso-alpha acids.

I talked to Dr. Denby and he confirmed to me that his yeast strains do not confer hop bitterness (his beer recipes for the paper did include hop pellets in the boil), but that the GM yeast do match or exceed natural hops in production of hops flavors and aromas after the boil. This means that the modified yeast could ease the strain on the hop producers and reduce the cost of bittering and flavoring hops for brewers. If a brewery could use transgenic yeast strains to produce a varied hop flavor/aroma profile in the fermenter, then the hops in the late boil, in fermentation, or the brite tank could be reduced or eliminated.

A considerable part of the hop harvest is used for dry hopping. It is these hops (and late boil additions) that might be replaced by GM yeast making terpenoids. photo credit: LA Beer Fan

This might actually open up brewers to even larger flavor/aroma profiles since they might only be able to afford a single hop for dry hopping, but could get many flavors out of modified yeast. It just depends on the number of genes added and controlled. And this says nothing of increased control it would afford brewers.

The fermenter is a scientific vessel; many aspects of the fermentation can be controlled and tweaked. This is much more control than anyone has over the weather during a growing period for hops. For example, each year the same variety hops will taste and smell a bit different because of weather and other factors. Even batches can vary, so brewers must rely on experience or trial and error to get the hoppy favor they are looking for. With yeast-produced hop flavors, the consistency of hop flavors can be ensured. Engineering the yeast might allow for putting a little art into your yeast science.

Matt Bochman, a certified yeast genius in the Department of Molecular & Cellular Biology at IU in Bloomington and a dedicated home brewer, talked to me about Dr. Denby’s research. He met Dr. Denby a couple of years ago at a World Brewing Congress and they discussed this research. Matt said he was very glad that it has finally been published so that maybe something can come from it now that it is in the public domain.

It would be nice if the conversation about GM foods stuck to the facts, but first we would have to agree as to what a fact is. image credit: almost a doctor’s channel

Dr. Bochman said that depending on the targeting of the plant DNA sequences, there might or might not be changes in the yeast function. If a gene was spliced into the middle of another gene, then that gene’s function could be altered or stopped. However, Matt was quick to point out that screens were done by Denby’s team to look for altered functions in the yeast, and only selected strains that were “normal” functioning. In truth, many proteins and other compounds are produced at an industrial level by modifying yeast to make and excrete them. So beer with yeast products replacing some of the hops would not be the biggest news in the scientific world this year, but it could make a difference to brewers and drinkers.

Let’s not be naïve, there are at least two other issues to this story. The first is the realization that hops can add much more to beer than just bittering, flavoring, and aromas. In heavily dry hopped beers there is a conversion of some hop compounds to terpenoids and other flavor compounds, and many of these come from hops. Yeast are not that picky when it comes to things they will metabolize; they will eat different sugars to be sure, but they will also eat glycosides and even break down some proteins.

Bioconversion of some hop compounds by yeast is what gives many NE IPA that juiciness and haze. photo credit: In Bounds Brewing

During dry hopping in the fermenter, some hop compounds get bio-converted, and this contributes greatly to the “juiciness” and some of the haze in New England IPAs. But even beyond this recent addition to the beer world, hops contribute chemicals that form insoluble complexes with proteins in beer, adding to its colloidal stability, contribute to head retention, and are the major antibacterial component in beer. True, there are styles of beer are made without hops, but in those that do use hops, you can’t really replace them – at least not yet.

Secondly, I am sure that there are some people out there, dedicated drinkers and causal fans alike, that might not want their beer messed with in such a manner. Even I, as a scientist who has done plenty of genetic manipulation in my day, am not completely at ease with GM yeast for beer. Not because I believe that GM organisms are a threat – I have read the studies both for and against GMOs, but because I like the purity of old fashioned beer.

Dr. Bochman understands that people might have issues with genetic modification because they are unaware of the measures taken, such as Dr. Denby’s screening experiments, and due to a lack of the basic knowledge of the processes and issues with gene manipulation. As a scientist, I understand that literally hundreds of studies and the meta-analysis of those studies have not shown negative health or environmental effects of genetically modified organisms.

Even though there is still a part of me that wants to see beer made the traditional way, but that doesn’t mean I think that there is no role for GM yeast in making beer. As long as I know what I’m drinking, I can appreciate both.

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