The Lab Rabbit celebrated Philadelphia’s science week with a heady combination of beer, yogurt, and sauerkraut. DIY Science: Fermentation was a workshop held at the venerable Di Bruno Bros. House of Cheese – a true hotseat of fermentation.
The workshop opened with a brief primer on zymology – the science of fermentation. Fermentation is basically taking sugar and converting it to an acid, gas, and/or alcohol. Usually bacteria or yeast is doing this dirty work. Buddy Muhler and Adam Piazza of the Franklin Institute demonstrated with Erlenmeyer flasks of yeast performing fermentation, and gave out samples of Yards Brewing Company’s Cerebral Pourtex beer. This alcoholic fermentation product, with grains as the starting material, is brewed especially for Science Week. For this workshop, our raw starting materials were cabbage and milk.
Fermentation demonstration. Photo Credit: The Lab Rabbit.
So much CO2. Photo Credit: The Lab Rabbit.
Cerebral Pourtex, by Yards Brewing Company. Photo Credit: The Lab Rabbit.
First, the cabbage. Amanda Feifer, of Phickle.com, got us started with large bowls of shredded cabbage, explaining that the cabbage is teeming with bacteria. Given the right environment, these bacteria start to gobble up sugars naturally occurring in the cabbage, and spit out vinegary-tasting lactic acid. (NB: Sauerkraut has a vinegary flavor not from acetic acid (a.k.a. vinegar), but from lactic acid, which is structurally very similar to acetic acid. Acetic acid is produced by, you guessed it – fermentation – of alcohol to vinegar.) Our first step was to massage our cabbage with a few tablespoons of salt – the salt draws out the water from the cabbage, providing a liquid environment in which the bacteria can do their work. The salt also kills some of the other bacteria present that might interfere with the fermentation process.
The Lab Rabbit tries her hand at making sauerkraut. So much cabbage. Photo Credit: The Lab Rabbit.
Amanda Feifer, of Phickle.com, demonstrates the sauerkraut making process. Photo Credit: The Lab Rabbit
Feifer explained that there are several stages of cabbage fermentation. First, anaerobic bacteria of genus Klebsiella (a rod-shaped bacteria that also lives in the human nose and gut) and genus Enterobacter (another rod-shaped guy that hangs out in the gut) lead the fermentation, producing lactic acid that paves the way to for the next wave of bacteria by creating an acidic environment. The second wave initiates when lactic acid builds up and lowers the pH of the cabbage-water-salt mixture. Those acid and salt-loving characters, Leuconostoc mesenteroides take over, while other bacteria that can’t handle the acidity die off. In the final phase, species such as Lactobacillus brevis and Lactobacillus plantarum gobble up any remaining sugars and convert them to lactic acid. The environment is now acidic enough that it prevents growth of Clostridium botulinum, the bacterium that causes botulism. The workshop left us with a jar of sauerkraut still in the first phase of fermentation – once we let it sit on the counter for about four weeks, we should have sauerkraut.
The Lab Rabbit’s sauerkraut – this will be fermenting on her counter for the next month. Photo Credit: The Lab Rabbit
We then moved on to yogurt. Feifer demonstrated how to make viili, a Finnish style of yogurt. This type of yogurt depends on a mesophilic bacteria – bacteria that prefers a moderate temperature, between 20 and 45 °C (68 and 113 °F). This is in contrast to thermophilic bacteria, which prefer higher temperatures. Thanks to the mesophilic bacteria, the viili can be made at room temperature.
The Lab Rabbit makes yogurt. Photo Credit: The Lab Rabbit
As with the sauerkraut, bacteria are key to the fermentation process. In this case, Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris are introduced to milk. They eat up the lactose (the sugar naturally found in milk), and produce, again, lactic acid. In the sauerkraut, the lactic acid imparted a vinegary flavor. But the milk is a different environment. Here, the lactic acid reacts with the casein proteins in the milk, causing the proteins to clump together. This is what gives yogurt its thick texture. If you’ve ever added something acidic, like lemon juice, to dairy, you’ve seen how the casein proteins curdle up. Feifer gave us each a sample ofmesophilic bacteria in starter culture. The Lab Rabbit brought this bacteria goodie bag home, to make her own batch of mesophilic yogurt*.
The evening wrapped up with a quick talk by Dr. Joseph Rucker, a chemist who reviewed the fermentation process and answered audience questions. You can find Feifer’s recipes for sauerkraut and yogurt on Phickle.com, and order your own bacteria for making yogurt on the Gem Cultures website.
*The Lab Rabbit’s Adventures with Mesophilic Bacteria: (All Photo Credits: The Lab Rabbit)
You start with some starter culture, full of bacteria…
Take a tablespoon of the starter, and smear it into a jar or bowl…
Once the sides of the jar are coated, up to around the 8 oz line, you’re ready to add milk. Eight ounces!
Now, cover it and let it sit. We let it sit for about 16 hours at room temperature.
The next morning, we had yogurt. Thanks, bacteria!