Does Eating Yeast Really Mitigate Alcohol Intoxication?

Jim Koch of the Boston Beer Company recently stated in an interview with Esquire Magazine that his secret to drinking without the intoxicating side effect was to eat  a teaspoon of baker’s yeast (mixed with yogurt). He claims that the enzyme alcohol dehydrogenase (ADH) in the yeast supplements our own ADH breaking down some of the alcohol reducing the amount that is absorbed by our bodies. Sounds too good to be true right? Well, I have a sinking suspicion that it is, so let’s take a look at the science.

Alcohol dehydrogenase in humans is an enzyme that catalyzes the reaction of alcohol to acetaldehyde that is found in the liver. It helps to clear alcohol from the body in a form that can be excreted. In contrast to humans, baker’s yeast have three types of ADH enzymes: ADH1, ADH2, ADH3 (similar to ADH1)¹. This is where things start to get a little fishy.

ADH1 in yeast actually reduces acetaldehyde and NADH to ethanol (making more alcohol) to regenerate NAD⁺, an important part of glycolysis (the cycle used to create energy from glucose)². As luck would have it, the most active form of ADH in baker’s yeast (the kind that Koch is eating) is ADH1¹. So essentially, as you’re breaking down ethanol in your body, yeast could be converting it back into ethanol canceling out what your body is doing increasing the effect of that beer.

The second form of alcohol dehydrogenase (ADH2), does in fact catalyze alcohol into acetaldehyde. The only issue is that ADH2 production is inhibited by the presence of glucose (sugar) in the environment³. So, Koch’s recommendation of mixing the yeast with yogurt would effectively repress the transcription of ADH2 reducing its activity.

If you’re still not convinced, the optimum range for these enzymes is in the neutral to alkaline range ¹. Your stomach, as I’m sure you know, is acidic (low pH), and would decrease the activity of the enzymes (if it didn't completely destroy them). Not to mention the fact that there are many beers produced that remain unfiltered, containing live yeast cultures in the beer, and do not lose the amount of alcohol in them as they age.

Sadly, it seems like the only way to "drink" without getting drunk is to stick with non-alcoholic beer (e.g. O'Doul's) or you could just drink responsibly, know your limits, and have a designated driver. If you have any other tips to mitigate the effects of alcohol while drinking let us know, and we will check them out to see if they are scientifically sound! Happy brewing.

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1. Leskovac, V., Trivic, S., Pericin, D. 2002. The three zinc-containing aclohol dehydrogenases from baker's yeast, Saccharomyces cerevisiae. FEMS Yeast Research 2:481-494
2.  Bennetzen, J.L., Hall, B.D. 1982. The primary structure of Saccharomyces cerevisiae gene for Alcohol Dehydrogenase I. The Journal of Biological Chemistry 257:3018-3025
3. Vallari, R.C., Cook, J.W., Audino, D.C., Morgan, M.J., Jensen, D.E., Laudano, A.P., Denis, C.L. 1992. Glucose repression of the yeast ADH2 gene occurs through multiple mechanisms, including control of the protein synthesis of its transcriptional activator, ADR1. Molecular and Cellular Biology 12: 1663-1673

Flavor Esters: An Introduction

Figure 1. Active flavor esters (adapted from Verstrepren et al., 2003)

Many of the fruity flavors (aromas) we perceive in a beer are in fact the products of yeast metabolism and not from the addition of fruits (Figure 1). Some of the esters produced by yeast are considered “off” or undesirable flavors, while others are appropriate at low levels. Some esters even give certain beers (e.g. hefeweizens) their characteristic taste.

To be perceived, the concentration of each ester must meet a specific threshold level; therefore, low levels of ester production will not impart any noticeable aroma. However, esters can have a synergistic effect on individual flavors, affecting overall beer flavor at concentrations well below their threshold⁽¹⁾.

Esters found in beer are synthesized from Acyl-CoA (a long chain fatty acid with Coenzyme A attached, which breaks down into Acetyl-CoA), and fusel alcohols by ester synthase enzymes (e.g. Alcohol acetyl transferase) found in yeast (Figure 2)⁽¹⁾. Beer is not the only place you will find esters; they can also be found naturally occurring in fruits and artificially in many of the candies we eat. In fact, the industry of flavor ester production is in high demand, producing esters for all of those artificially flavored foods and drinks we love to consume in addition to the cosmetics and pharmaceutical industries⁽²⁾.

Figure 2. Enzymatic ester synthesis (Verstrepren et al., 2003)

Unlike ester synthesis in beer, the majority of flavor esters for these industries are produced in labs by chemically synthesizing each compound (Figure 3)⁽²⁾. Recently, the growing trend for “natural foods” has generated a push against the consumption and use of products containing artificial ingredients. These industries have responded by turning to the noble yeast, albeit a different genus and species from those used for brewing, to enzymatically synthesize esters. Esters produced by this process can be labeled as “natural” quelling the fears of the chemically conscientious consumers⁽¹⁾.

Figure 3. Chemical ester synthesis

But I digress...Back to the important things in life, brewing! Temperature, specific-gravity, oxygen, fusel (German for “hooch”) alcohols, and fatty acids all have effects on the production of esters but they may vary depending on the yeast strain. There is a direct relationship between temperature, specific gravity, fusel alcohols, and activated fatty acids (Acyl-CoA, and Acetyl-CoA) with the production of esters⁽¹⁾. The manipulation of these factors is important when considering the style of beer you plan to brew. In general, ales contain higher levels of esters than lagers in part because of the yeast species used (read more) as well as the higher temperatures used during ale fermentation ( above 58°F) compared to those used to "lager" (32°F-56°F). In the next esters post I will talk about each about each factor in greater depth and the mechanism by which they modulate ester production. Until then, happy brewing!

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1. Verstrepren, K.J., Derdelinckx, G., Dufour, J.P., Winderickx, J., Thevelein, J.M., Pretorius, I.S., Delvaux, F.R. 2003. Review: Flavor-Active Esters: Adding Fruitiness to Beer. J Bioscience and Bioengineering 96(2): 110-118 
2. Larios, A., Garcia, H.A., Oliart, R.M., Valerio-Alfaro, G. 2004. Synthesis of Flavor and Fragrance esters using Candida antartica lipase. Appl Microbiol Biotechnol 65:373-376

A Tale of Two Yeasts

It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, and where there was one, now there are many, yeast that is. No this is not some Dickens’ novel but the real life tale of brewer’s yeast. Most homebrewers are aware that there are generally two types of yeast used to make beer, ale yeast (Saccharomyces cerevisiae) and lager yeast (Saccharomyces pastorianus aka S. carlsbergensis), but things are rarely as simple as they seem.

The domestication of barley in Sumeria 6,000 years ago likely led to the predecessor to modern day beer and the beginnings of yeast domestication. During the Middle Ages in Europe, ale-type beers (likely brewed with Saccharomyces cerevisiae) were beginning to be produced with lager-brewing arising in 15th century Bavaria⁽¹⁾. The first yeast strain (CBS1171) wasn’t isolated until 1883 by Emile Christian Hansen and was designated as the neo type (specimen a species is named for) of Saccharomyces cerevisiae. This isolation led to the first pure cultures of yeast strains used for commercial beer production in the late 1800’s⁽²⁾. It was generally recognized that ale and lager yeasts were different but it would take another 100 years to identify that difference (Figure 1).

S. cerevisiae 

S. pastorianus 

S. bayanus

Figure 1. See why yeast species identification is difficult. All three species are part of the Saccharomyces sensu stricto group.

In 1985, the Saccharomyces group known as Saccharomyces sensu stricto were split utilizing DNA analyses into four distinct species: ale style yeast, S. cerevisiae (neo type strain CBS1171NT); wine and cider yeast, S. bayanus (CBS380T); S. paradoxus (CBS432NT); and lager yeast, S. pastorianus (CBS1538NT)⁽³⁾. These experiments also revealed that S. pastorianus (lager yeast) was a hybrid species with S. cerevisiae and another species ⁽⁴⁾, but more on that coming up. Since 1985, this group has been divided into even more species. Many of these species are differentiated by only a few nucleotide base pairs at certain chromosomal loci known for sugar (maltose) and sulfite metabolism. Some species are allotetraploid hybrids (a duplication of each chromosome from the parents) or sterile haploids and diploids incapable of sexual reproduction, but yeast reproduction can be saved for another post.

As you can see, yeast genetics is complicated and contentious. Lager yeast (S. pastorianus) unlike ale yeasts, have never been isolated from the wild and depends on humans for its propagation ⁽⁴⁾. In 2011, scientists identified a cryotolerant species of yeast (S. eubayanus) in Patagonia that is likely the missing parent of lager yeast (Figure 2). These yeasts were isolated from beech trees and their associated fungi (Cyttaria sp.) in the Southern Hemisphere. These beech trees are equivalent to their northern cousins, oak trees ⁽⁵⁾. Saccharomyces spp. are often associated with oak trees in the Northern Hemisphere and are thought to be the origins of brewers and baker’s yeast in Europe. How South American yeast made their way to Europe is still under some debate. Some believe the early trade routes may have brought back exotic wood and the yeast hitched a ride to European breweries. Others believe that fruit flies stowed away on shipping vessels may have carried S. eubayanus in their guts until finding their way to Europe ⁽⁵⁾. We may never know how S. eubayanus found their way to Bavarian breweries but they have helped to create one of the most popular and commonly used yeast in the brewer’s arsenal. Prost!

Figure 2. Cyttaria from Chile growing in a tree branch where S. eubayanus was isolate   

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1. Corran HS (1975) A History of Brewing (David and Charles, London, UK).
2. Nguyen H-V, Legras J-L, Neuve´ glise C, Gaillardin C (2011) Deciphering the Hybridization History Leading to the Lager Lineage Based on the Mosaic Genomes of Saccharomyces bayanus Strains NBRC1948 and CBS380T. PLoS ONE 6(10): e25821. doi:10.1371/journal.pone.0025821
3. Vaughan-Martini A, Kurtzman CP (1985) Deoxyribonucleic Acid Relatedness among Species of the Genus Saccharomyces Sensu Stricto. International Journal of Systematic Bacteriology 35: 508–511.
4. Dunn B, Sherlock G (2008) Reconstruction of the genome origins and evolution of the hybrid lager yeast Saccharomyces pastorianus. Genome Res 18:1610–1623.
5. Libkind et al. (2011). Microbe domestication and the identification of the wild genetic stock of lager-brewing yeast. PNAS 108:14539-14544.

Yeast, the Modern Day Alchemist: Part 1 --Phenols

Have you ever had a beer that tasted like it had those little Runt bananas in it or a Belgian ale that you knew had to have cloves added. Well in many cases what you tasted was not coming from fruit or spices but are the products of yeast.

Brewing yeast, Phylum Ascomycota, class Saccharomycetes (Latin for sugar fungi), is a humble cousin to one of the most expensive foods on the planet, the truffle. Under the guise of their grunt work consisting of converting sugars to alcohol (Figure 1), they clandestinely spin some of the alcohols and other products into flavorful and aromatic gold, like an army of microscopic Rumplestiltskins. They won’t steal your first born, but they may spin some flavors that you weren't asking for if you’re not careful. Of course we know that alchemy never seems to work so here’s how they are actually making some of these compounds that give different characters to beer.

Figure 1. Simple Ethanol Fermentation.(from Wikipedia.org)

Yeasts can produce a couple different types of products in addition to the well-known alcohol and CO2. These include various esters and phenols. For the sake of keeping this post relatively short I’m just going to talk about phenols and leave the esters for later.

4-vinylguaiacol, perceived as clove can be produced by thermal decompsition of the carboxyl group in ferulic acid. In addition, yeast enzymes called feruloyl esterases (figure 2) can also decarboxylate ferulic acid to form 4-vinylguaiacol. The amount of this phenol can vary greatly depending on the specific yeast strain used to ferment the wort. Grain can also contribute to the initial abundance of ferulic acid available for conversion. While the majority of ferulic acid was released during the brewing process of barley, 60-90% of ferulic acid was hydrolyzed during fermentation in beer containing wheat malt ⁽¹⁾ which leads to a greater amount of that tasty clove-like spicyness found in many Belgian style beers.

Figure 2. Conversion of Ferulic Acid to 4-vinylguaiacol

Another type of Phenol that you may run into is 4-ethyl phenol. This one is certainly for the more adventurous beer drinker. It lends the “barn yard” or “horse blanket” character to beers fermented with the wild yeast Brettanomyces sp. Typical styles include the farm-house ales, not because they taste that way, but because they were historically fermented in open containers during the cooler months to reduce the chance of getting nasty microscopic bugs. Although, it seems like brewers would want to steer clear of this character, it does lend a certain complexity to beers and can be quite enjoyable.

Now for the synthesis! Cinnamate decarboxylase removes the carboxyl group from p-coumaric acid to produce 4-vinylphenol, which is then reduced by vinyl phenol reductase to create the final product 4-ethylphenol. Like ferulic acid, p-coumaric acid can be found naturally occurring in grains. Interestingly, a study found that organically produced wheat had significantly higher concentrations of both ferulic and p-coumaric acid ⁽²⁾.

Figure 3. Synthesis of 4-ethylphenol from p-coumaric Acid (From Wikipedia.org).

Be adventurous, try a farmhouse ale. Maybe you’ll like it, or maybe you will want to scrape your tongue off with a putty knife. Either way, at least you’ll know how it’s synthesized and that should count for something.

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1. Coghe, S., Benoot, K., Delvaux, F., Vanderhaegen, B., Delvaux FR. 2004. Ferulic acid release and 4-vinylguaiacol formation during brewing and fermentation: indications for feruloyl esterase activity in Saccharomyces cerevisiae. J Agric Food Chem 52(3): 602-8 
2. Zuchowski, J., Jonczyk, K., Oleszek, W. 2011. Phenolic acid concentrations in organically and conventionally cultivated spring and winter wheat. J Sci Food Agric 91(6): 1089-95