How sour beer gets so... sour

Date:
August 17, 2020
Source:
American Chemical Society
Summary:
Sour beer has recently surged in popularity in the US Today,
scientists report progress on a study of how acids and other flavor
components in the beverage evolve as it ages. Their goal is to
help brewers understand and gain more control over the taste of
this tart and tangy drink.



FULL STORY ==========================================================================
Sour beer, the tart and tangy outcome of a brewing process that's been
used in Europe for centuries, has recently surged in popularity in the
U.S. Today, scientists report progress on a study of how acids and other
flavor components evolve while the beverage ages. Their aim is to help
brewers understand and gain more control over sour beer's taste.


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The researchers will present their results at the American Chemical
Society (ACS) Fall 2020 Virtual Meeting & Expo.

A brand-new video about the ongoing research is available at http:// www.acs.org/fall2020-sour-beer.

Sour beer is an ancient type of beer in which wild yeast and bacteria are allowed to grow in freshly brewed beer (wort), which then ferments. After
this stage, the wort is often transferred to wooden barrels where it
matures for months or years. During that time, the microbes produce
numerous metabolic products -- including ethanol, acids and esters
-- that provide much of the unique flavor of sour beers. The barrels
themselves can infuse trace components, such as vanillin and catechin,
that contribute to the flavor profile.

"Scientists are very interested in beer and especially sours because
they are such complicated systems," says Teresa L. Longin, Ph.D., one of
the project's principal investigators. "There have been several prior
studies of the components in finished sour beers. What makes our study different is that we've been able to get samples of beer in progress
from many different batches." Their findings could help brewers make
better products.

Longin was drawn into the study by her husband and co-PI, David
P. Soulsby, Ph.D., and both are at the University of Redlands. When
Soulsby began the project a couple of years ago, he reached out to Bryan
Doty, a master brewer at nearby Sour Cellars. Doty was eager to learn
what was going on in his beer and has provided a series of samples from
the same barrels as the beer has aged.

Soulsby and undergraduate student Alexis Cooper examined each sample using
NMR spectroscopy coupled with a new analysis method for quantitating
the data. They used this approach to track the levels of acetic acid,
the main component of vinegar; lactic acid, which gives sourdough bread
its distinctive taste; and succinic acid, which is found in broccoli,
rhubarb and meat extracts. They found that each acid stabilized at
similar concentrations in the different batches, though some batches
had greater variability. "These organic acids give sour beers a lot of
their flavor, and the balance of organic acids produces very different
types of sour beer," Longin says. "It can be more like balsamic vinegar,
which has a sweet/sour flavor, or it can be 'puckery' sour. So the mix of organic acids is really important for understanding the flavor profile." Working with Emily Santa Ana, one of the undergraduates in her lab,
Longin drew on expertise in liquid chromatography/time-of-flight mass spectrometry to search for other compounds that contribute subtly to
flavor but are present at levels too low to detect with NMR.

"This is a work in progress, but I'm definitely seeing some trace
compounds that are changing over time," Longin says. Some compounds start
off at high concentrations and then disappear; they might be sugars
that are being consumed by yeast as they produce ethanol and carbon
dioxide, and by bacteria as they form organic acids. Others "grow in"
over time. They could be additional organic acids, health-promoting antioxidants known as phenolics, or vanillin, which lends a hint of
vanilla to beer.

The researchers will use the mass spectrometry data to identify the
trace compounds and determine whether they come from the barrels or from byproducts of yeast or bacteria metabolism. "In addition, if a brewer
knows a particular combination of yeast and bacteria produces a desirable flavor profile, they can culture more of it," Longin says. "Or if they
know that a beer with a specific combination of acids is especially
pleasing, they'll know when to stop aging the beer so it doesn't lose
that balance."

========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


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Link to news story: https://www.sciencedaily.com/releases/2020/08/200817104313.htm

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