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Friday Happy Hour #3: Pumpkin Beer, Flavor Generation and Brewing Adjuncts

The views expressed are those of the author and are not necessarily those of Scientific American.


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I’m doing a monthly series here at Food Matters that I’m calling “Friday* Happy Hour,” in which I’ll delve into the science of alcohol production.

For your consideration: 4 wonderful pumpkin ales.

I was really excited about this month’s Happy Hour. I’m a huge fan of pumpkin beers, and there are so many to chose from. I’ve been saving a bottle from all of the 6-packs I’ve purchased since the end of August when pumpkin beers start getting sold, and I had seven different varieties to compare. I decided that drinking seven beers in one evening was a recipe for suffering though, so I settled on four: Post Road (from Brooklyn Breweries), Smuttynose, Saranac and Dogfish Head.

Last month, See Arr Oh gave us a primmer on pumpkin flavor, and the molecules that impart it:

For pumpkins, shorter chains apparently rule the day. When you first slice into one, note the clingy, vegetal odor. That’s major aroma constituent cis-3-hexenol, a six-carbon compound also known as ‘leaf alcohol.’ Close chemical cousins n-hexanol and 2-hexenal round out the top 3 smells, according to the authors. Notice a buttery undertone? Diacetyl, the flavor behind movie-theater butter (and the industrial medical condition “popcorn lung”) occurs naturally in pumpkin.

Most of the beers in my little one-man taste-test didn’t actually taste strongly of pumpkin, but they all give me the opportunity to talk about something incredibly important to beer-brewing generally: adjuncts.

Where Flavor Comes From

Traditionally, all beers are the product of four things: water, malted barley, hops and yeast. Despite the paucity of ingredients, these four elements can impart an impressive variety of flavors. Flavor generally is a combination of your taste buds’ perception of salty, sour, sweet, bitter and umami, and your nose’s perception of aromas, which are mostly small, volatile compounds. I’m going to leave the psychology and physiology of flavor to someone with a bit more knowledge, but the  thing to know for this post is that the variety in beer flavors are of the aromatic variety.

The small molecules that contribute aromas can come from a number of different sources. Oils from hops have quite a few flavorful compounds, and different varieties of the plant have different quantities of these oils. Malted barley can be roasted before brewing, imparting some burnt or smokey flavors. But by far the most variety is imparted by the yeast, which during fermentation generate a huge number of secondary metabolites that end up in the beer. Different strains of yeast produce different amounts of these compounds, and for many  beer producers, the strains of yeast used in their breweries are a closely protected secret.

And it’s not just as simple as “yeast strain A makes X amount of Y compound,” the balance can be affected by the quality of water, the source of carbohydrates, or the time of brewing. For instance, the buttery diacetyl that SAO mentioned in his pumpkin post is a compound that most brewers try to avoid like plague, but many strains of yeast produce it quite early during fermentation. The good news is that the microbes can also absorb and utilize diacetlyl as other sources of energy dwindle, turning into flavorless compounds or compounds with a more beer-friendly taste. This means that brewers must take care not to end fermentation too soon, otherwise the buttery flavor will remain.

The Use of Adjuncts

Though there are four ingredients that all beers contain, many beers contain far more. Some adjuncts, like wheat, corn and rice are used as additional (often cheaper) sources of carbohydrates for the yeast to consume and turn into alcohol. Other adjuncts are used for flavor – spices like nutmeg, cloves and cinnamon are popular in winter beers for instance. My favorite beer of late, Grey Lady from Cisco Brewery tastes like it has bergamot (like earl grey tea).

But for this month, we’re concerned with pumpkin or pumpkin-like adjuncts. As SAO noted in his post, the “pumpkin spice” you might find in your Starbucks latte may not actually contain any pumpkin. Pumpkin beers are no different.  Of the four beers I tasted, only the Saranac contains no pumpkin at all [Rich from Saranac got in touch with me for a correction: turns out that there's over a ton of pumpkins in each batch... my bad] – only cinnamon, allspice, cloves and vanilla. Smuttynose claims to add pumpkins (though no indication of how much) and “traditional spices,” while Dogfish Head uses “pumpkin meat, brown sugar and spices.” Post Road doesn’t mention any spices, just “hundreds of pounds of pumpkins.”

The Taste-Test

Unfortunately, despite my months-long preparation in gathering the beers for this post, when it came time to actually doing the taste-test, I did something stupid – I ate a rich, chocolatey dessert, and my palate was completely ruined for the evening. Maybe I should do a post on how the senses are affected by feed-back loops or something, but alas, a careful comparison was not in the cards. I can say from previous experience that all four are delicious, so I guess you’ll just have to do the taste test on your own. But probably not until next year, because these things aren’t on the shelves anymore. Oh well.

I actually ended up putting two of these bottles back in the fridge for later – even four beers was too much for one night. I’m not in college anymore.

——–

*I know it is no longer Friday – the holiday usurped my blogging. Hope everyone had a happy Thanksgiving!

Kevin Bonham About the Author: Kevin Bonham is a Curriculum Fellow in the Microbiology and Immunobiology department at Harvard Medical school. He received his PhD from Harvard, where he studied how the cells of the immune system detect the presence of infectious microbes. Find him on Google+, Reddit. Follow on Twitter @Kevbonham.

The views expressed are those of the author and are not necessarily those of Scientific American.






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