Speeding up Sour Beer Production… with Field Peas?

Sour beers require longer, more complicated brewing processes compared to their less-mouth-puckering peers—potentially on the order of years—which is why they tend to be rarer and more expensive.

Fortunately, scientists have recently innovated a method for making quicker, more intensely flavored sours. The weird part? Those recipes use field peas, of all things.

Sculpting Spectacular (Sour) Beers

Production of unsoured beers like lagers relies on the Saccharomyces genus of yeast. In basic terms, a pinch of yeast is a menagerie of unicellular little fungi; everything needed for life, and flavor, packed inside convenient, single-celled packages. Therefore, these microscopic fungi actually are fun guys, if you’ll excuse the old adage.

Beyond the cutesy semantics, the main takeaway is that this is a fungus, and the byproducts it yields during fermentation lend cleaner, conventional beer flavors. 

But sour beer production is more feral, unpredictable, and dependent on a complex interplay of microbes and yeast—a real Wild West microcosm in your glass.

Sour Beer Specifics 

Sour beers get their signature taste and tang from lactic acid, provided by lactic-acid-producing bacteria (LAB) such as Lactobacillus and Pediococcus, whose fermentation byproducts are acidic and much funkier. 

Endearingly nicknamed “Lacto” and “Pedio,” the aforementioned microorganisms aren’t fungi, like yeast, but they, too, consume sugars and create flavorful byproducts through their tiny metabolisms. In this case, lactic acid, as might have been gleaned by the preceding paragraph.

 Carbonic acid, coming from dissolved carbon dioxide, and the vinegary acetic acid also often alter a sour beer’s milieu. For tasting notes, lactic acid is usually “felt on the tongue,” while acetic acid introduces itself on the back of the throat.

Fungi and Bacteria Team Up to Create a Mosaic of Flavors

The various LAB may be used alongside Brettanomyces, a strange, free-spirited yeast species described circa 1903 by N. Hjelte Claussen at the Carlsberg Research Laboratory in Copenhagen, Denmark. Its name means “British yeast” in Greek. 

Brettanomyces, known simply (but not always endearingly) as “Brett,” can be isolated from an odd variety of sources, including kombucha, kefir, fruit peels, wooden barrels, and fruit flies. Alas, this yeast can also be a brewer’s nightmare, causing beer and wine spoilage by creating byproducts with flavors described as “horse sweat,” among other, less-disgusting barnyard notes.

Yet in the hands of an experienced sour-smith, this yeast provides a mouth-watering bouquet of pineapples, mangos, grapes, and pears. Also, sometimes, that “sweaty leather horse blanket” descriptor is just what the brewer is going for.

The LAB or yeast can be added by brewers or introduced naturally from the environment, whether intentionally or accidentally (see: fruit flies). For example, when Dogfish Head brewed their historical Ta Henket Egyptian brew, they set out Petri dishes to “capture” Cairo’s local yeast strains. 

Yet here’s the issue: microbes like LAB can be slow eaters, often needing “months or even years to ferment the original sugary, steeped-grain liquid (wort) into a desirable drink,” per the American Chemical Society.

Speeding Up the Sour Timeline 

To expedite sour beer brewing, scientists auditioned an unexpected ingredient: field peas. Sugars from field peas, to be exact, which were extracted and fed to acid-making microbes. 

For context, field peas belong to an under-appreciated family of plants called the pulses. Pulses are, according to their very own website, the “edible seeds of plants in the legume family.” Most notably they include lentils, beans, and, of course, peas, a sustainable and easy-to-grow crop.  

So, why has no one else tried anything like this before? Surely, some mad-scientist experimentalists must have attempted wackier ingredients. In fact, they have. A group of mostly different study authors did previously attempt an even more unconventional sugar source: wood. Literal wood. 

Birch Wood Sours

The researchers in said study fed their microbes with birch wood sugars, from the terrible-sounding sugar-family the “xylooligosaccharides” (XOS). We humans can’t readily digest these, but some among our kind do laud their potential as a prebiotic. And for etymology purposes, the ”xylo-“ prefix includes all things related to wood, including wood itself. 

Overall, the experiment worked, by some measures. The resultant sour beer sped up production prodigiously, from years to a month. Furthermore, the wood-soured beer was assessed similarly to a “commercial reference” in numerous attributes, including acidity. Yet still, birch wood sours fail to adorn the shelves. 

Feeding Field Peas to Bacteria 

The primary issue with using peas and other pulses in brewing is that they lend a “beany” aspect to beverages and foods. That’s certainly not as bad as horse sweat, some might say, but it isn’t generally desired in a sour beer, or perhaps any other type of recreational beverage. 

Yet on the other hand, field peas contain sugars known as raffinose-family oligosaccharides (RFOs), providing an appreciated food source for acid-producing bacteria.

The Experiment 

Described in the Journal of Agricultural and Food Chemistry, the researchers used three types of LAB to brew four experimental sour beers with a species of the Brettanomyces yeast mentioned earlier. Two of these experimental beers used the field-pea sugars (RFOs) and two did not. The beers were fermented for 19 days before being chemically analyzed, as well as evaluated by a “trained sensory panel.” 

Souring the results (in a good way)

The field peas scored big. The beers brewed with the pea-derived sugars featured more lactic acid, ethanol (alcohol), and a greater blend of fruity-flavor compounds. As a result they were more acidic, fruitier, and more intense—yet not overpoweringly so, with a “total taste intensity comparable to the commercial beer.” 

And while the field pea sugars can be indigestible and cause gastrointestinal distress, there were no traces left in the beers because the LAB “gobbled” them up. This comprehensive gobbling isn’t just beneficial health-wise, but also industrially, showing that the microbes completely metabolized the pea-sugars despite a rushed fermentation timeline.

Lentils, Peas, and Beans, oh my 

Equally essential, the experimental beers did not taste like beans. Or peas, for that matter—though this vital fact probably won’t make the sales pitch when field-pea sours inevitably hit the market.