Announcing STEM in Style: A Celebration of Women in STEM -- Click here to learn more!

Actual Living Scientist: Andrew Gierczak, Brewer and Founder at MobCraft Beer Inc.

Grains, hops, yeast, and water: the four basic ingredients required to make beer. While this recipe may seem simple, the smallest variation on any of these elements can drastically alter the overall composition of the frothy end product. As head brewer at MobCraft, Andrew Gierczak is a master of these elements.

Andrew, a Milwaukee native, earned a bachelor’s degree in microbiology from UW-Madison. Before MobCraft’s inception, Andrew worked in an analytical quality control lab and was an active home brewer. Andrew and some of his closest friends would concoct unique beers based on suggestions submitted by their acquaintances; the success of this hobby laid the groundwork for what would later be formalized as MobCraft, the world’s first crowdsourced brewery.

Andrew employs scientific practices and principles at each step of the brewing process, starting with ingredient selection. True to their crowdsourcing roots, MobCraft runs a monthly competition that allows patrons to formulate new beers that will eventually be sold in the Walker’s Point Taproom and on the MobCraft website. Once the winning beer style and flavor profile have been selected, Andrew wrangles the appropriate grains, hops, yeast, and non-traditional fixings to be featured in that specific brew. To date, Andrew cites durian as the most unique ingredient used in a MobCraft beer. Native to Southeast Asia, durian is a fruit that emits a pungent smell reminiscent of onions or cat urine, but that possesses a sweet creamy taste similar to that of vanilla mango custard. No ingredient is too bold for the MobCraft team; according to Andrew, brewing is all about flavor balance and when properly mixed, even the craziest ingredients can make an excellent addition to beer.

The durian fruit is the most unique ingredient MobCraft has incorporated into a brew thus far. Pictured on the right is equipment Andrew uses a daily basis: a sterilizer, incubator, and refrigerator.

Beer is one of the end products of a process known as alcoholic fermentation. In this reaction, single-celled yeast break down sugar into alcohol and carbon dioxide. In the brewing process, sugar comes from the different grains. While barley is the most commonly used grain, wheat, rye, oats, and other crops can be added to the mix to change the flavor. In order to break down the sugar into a form that the yeast can digest, all grains must be sprouted in a process known as malting. Malting also gives grains a distinct “browned” flavor similar to those tasted in baked bread, roasted marshmallows, and seared steaks. This flavor is created through a chemical process known as the Maillard reaction.

Crushed malted grains are next soaked in hot water in order to convert and release sugars. As you might have guessed, water chemistry is also important in the brewing process. MobCraft uses conditioned Milwaukee city water for all of their brews, and takes special care to ensure that the proper amount of salts are maintained in the liquid. According to Andrew, proper brewing of darker beers like stouts and porters relies heavily on water “hardness,” a measure of calcium and magnesium in the water. The sugary water, known as wort, is next filtered and sterilized before hops are mixed in. At each stage of the brewing process, it is critical that no intruder microorganisms be present. One of Andrew’s daily jobs at MobCraft is to sterilize the tanks with a blowtorch and spray alcohol. During brewing, Andrew collects beer samples and mixes them with media, a solution in which specific types of microorganisms grow quickly. Andrew uses both solid and liquid media at MobCraft; he allows the inoculated media, or media that has been mixed with the tank or beer sample, to grow in a 98 degree F (37 degree C) incubator for several days then checks for presence of life. If the media, which is a transparent yellow when sterile, is cloudy or has gas bubbles after incubation, this a sign of unwanted microbes. Andrew learned many of these basic microbiological techniques during his time at UW-Madison and plans on bringing even more complex tests to MobCraft in the near future.

Inside the incubator, Andrew keeps media that has been mixed with different solid and liquid samples from across the MobCraft brewery. Tubes and plates are labeled with the date and source of each sample.

Hops are the next ingredient added in the brew process. The addition of these flower cones not only add flavor to each beer but also help to preserve the final product. The bitter flavor of many beers, measured in IBUs or international bittering units, is derived from early addition of hops during the brewing process. Andrew says hops science is a rapidly growing field even here in Wisconsin; MobCraft sources their hops from two local growing collectives.

The last, and most critical addition to the brewing liquid is yeast. Yeast are the living organisms that actually perform the fermentation process that produces beer. Depending on the strain or specific type of yeast, fermentation may take a few days or several months. The temperature at which fermentation occurs can also vary greatly; yeast strains that ferment at room temperature end up producing ales while those that ferment in the cold produce lagers. Yeast can be reused for several batches of beer. Andrew assesses yeast viability, or overall health, using different dyes and a microscope. He can tell if yeast are up to the challenge of fermentation before adding them into a brew.

Andrew uses a microscope to assess yeast health and to identify types of bacteria that may appear in cultured media samples.

After fermentation is complete, Andrew and other members of the MobCraft team put their taste buds to the test and sample the end product. While this might sound like a fun task, Andrew states that he had to train his taste buds with a lot of BAD beer in order to develop a palate that can distinguish what the industry refers to as “off flavors”. These discrepancies arise as part of the brewing process, and again can be explained by science. One of the most common off flavors is that of artificial butter. Beers tasting like this contain a high level of diacetyl, a compound that results from the fermentation pathway being stopped too soon. Andrew also cautions home brewers against using any bleach when cleaning their supplies. Excess bleach can add chlorine to the brew base, which the yeast then metabolize into a compound called to chlorophenol. This chemical has a distinct flavor that Andrew describes as “medicinal, almost band-aid like”.

Andrew’s background in basic science is evident to anybody who watches or listens to him work. He speaks like a well-versed biochemist and microbiologist reciting all of the chemicals and enzymes involved in the many steps of the brewing process. Andrew says science has an indisputable role not only in Milwaukee, but also more broadly in the state of Wisconsin. Thousands of jobs in the state, including those in the brewing and dairy industry, fall under the food science label. In fact as of 2016, Wisconsin has the fifth highest concentration of food scientists in the country!

In closing, Andrew comments on the magic that is beer brewing. Andrew states that this magic is just “science that we don’t yet know. I understand some aspects of what I do, but not all of it. And I think that’s a beautiful place.” Want to learn more about MobCraft and their unique business model? Check out their website: or visit their Walker’s Point Tap Room: 505 South 5th Street, Milwaukee.

Written by Kate Sadler for the Milwaukee Area Science Advocates (MASA)

Leave a Reply

Your email address will not be published. Required fields are marked *