Friday, 30 September 2016 02:39

Food for Thought: Microbes and Fermented Food

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Published in Microbial Sciences

Yeast agar plateFigure 1. Saccharomyces colonies, a popular yeast for fermentation. Source

Microbiology offers us a nearly limitless world of microbes and their biological processes to study.  However, while microbiologists may differ in their specific fields of interests, we all agree that one area in particular takes the cake, or rather bakes the cake: food microbiology. Since early human history, microbes have been helping us in the kitchen. From beer to kimchi to yogurt, these tiny chefs play critical roles in food production processes through the chemical reactions they perform. Most notably they engage in fermentation, converting sugars and carbohydrates to alcohols, gases, and/or acids, but other reactions help produce additional signature flavors and textures.

In industrial settings, technicians and researchers must work hard to outsmart would-be contaminants and improve the production process. Keeping equipment clean isn’t enough to prevent the growth and spread of spoilage-causing contaminants. For example, Lactobacillus casei and Lactobacillus paracasei ($) will spoil pickles unless the brine mixture is altered to stop their activities. Additionally, in cheese production, different strains of the desired lactic acid bacteria are cycled to outpace the bacteriophages that inevitably multiply and cause infection and product loss. While some efforts of food microbiologists are defensive, others are creative and inventive. Through genetic and metabolic analyses of key cultures, food microbiologists are able to create new strains with improved function. For example, in sake production foam is undesirable, but chemical foam control agents add additional costs. Researchers have not only isolated variants of Saccharomyces cerevisiae that do not produce foam, they have also identified the gene responsible for foaming.  Furthermore, a range of sequence-based molecular biology techniques have given researchers a picture of the diversity of microbial species involved in fermenting foods. This diversity covers yeasts and filamentous molds, Gram-positive and Gram-negative bacteria, and even Archaea.

Figure 3SBFFigure 2. Festival-goers at the Santa Barbara Fermentation Festival learning how to make sodas with cold-infused plants.  Photo Credit: Janet Goins

While these large-scale, professional efforts are impressive, food microbiology doesn’t just happen at the industrial level; it’s part of the average kitchen as well. In fact, there are growing movements to encourage more people to take advantage of the vast range of microbes’ culinary talents. For example, there are numerous articles, books, and even classes on how to ferment foods. Additionally, there are events dedicated to showing people how to create their own fermented foods at home, like the Santa Barbara Fermentation Festival, which I attended two weeks ago. Through booths and workshops, participants learned how to make their own kefir, yogurt, miso, sauerkraut, and other fermented foods.  This year the fermentation festival also brought in people to talk about the human gut microbiome and its relation to our health and diet, which is a topic I’ll discuss further in a few weeks.  For now, I’ll stick with food fermentation and what you can do at home.

Figure 4SBF2Figure 3. Festival-goers at the Santa Barbara Fermentation Festival enjoying the Farm-to-Bar area and the brews of guest exhibitors.  Photo Credit: Steven Goins

Among the products made by homemade microbiology, beer is without a doubt king, and any discussion of food microbiology would be remiss without giving it special mention. At the Santa Barbara Fermentation Festival, the Farm-to-Bar area provided a venue for brewers to share their craft (a wide variety of ales and lagers, plus a highly recommended mead, called JUN, from The Apiary) and stories with homebrewers and would-be homebrewers alike. This year, a panel that included Patrick Ceriale of Telegraph Brewing Company, Nancy Oster (a local baker), James Burge of Pure Order Brewing Company, and Charles Williams of Broken Clock Vinegar Works discussed their experiences and answered audience questions. The key take-homes from this and many of the other food-fermenting stations boiled down to several lessons for the home fermenter.

First, start with high-quality ingredients. This is advice that any chef will give, and it was echoed here along with the advice to start by thinking of what you want your end product/tastes to be. Second, keep your space and equipment clean and keep utensils separate from one another to prevent cross-contamination. As Ceriale put it, “half of your job is being a janitor.” Third, when it comes to getting the cultures you do want growing, be adventurous. While a number of starter cultures are available for sale, all four panelists encouraged audience members to try their luck with what can be found in their local environments. Oster suggested placing a pan of sugar water under a peach tree as one experiment, while Williams shared that fruit flies are especially helpful agents for transferring desirable Acetobacteria for making vinegar. He recommended that if you find a fruit fly in your wine, cover the top with cheesecloth and wait ~6-8 weeks. Fourth, start small with any of your first cultures and then propagate to larger quantities later. Finally, patience is key. Not all experiments will work out to tasty brews or breads, and some will require multiple attempts to get right.  Oftentimes contamination or mistakes will force you to start over, but sometimes they will provide a serendipitous delight, such as one of Ceriale’s brews that is the product of an accidental cross-contamination between a Lactobacillus culture and a Brettanomyces culture.

Kombucha Figure 4. Jar of kombucha. The thick, slimy layer at the top is the SCOBY or Symbiotic Colony of Bacteria and Yeast which are the microbes responsible for fermentation. Source

With so many fermented foods to taste and make as well as the endless possible variations, brewing up some homemade microbiology in your kitchen will undoubtedly quench your hunger, thirst, and curiosity. And if that isn’t enough to satisfy you, check out Moyashimon, an anime that introduces the microbial characters involved in food fermentation in an amusing yet educational manner. Regardless of your specific tastes, these microscopic chefs likely play an important part of your diet, so let’s drink a toast (of your fermented beverage of choice) to these hardworking fermenters.  Cheers!

Further Reading

Bokulicha, N.A. & Bamforth, C.W. (2013) The Microbiology of Malting and Brewing. Microbiology and Molecular Biology Reviews, 77(2), 157-172.

Pires E.J., Teixeira J.A., Brányik T., & Vicente A.A. (2014) Yeast: The Soul of Beer's Aroma—A Review of Flavour-active Esters and Higher Alcohols Produced by the Brewing Yeast. Applied Microbiology and Biotechnology, 98(5), 1937-1949.

Tamang, J.P. Watanabe, K. & Holzapfel, W.H. (2016) Review: Diversity of Microorganisms in Global Fermented Foods and Beverages. Frontiers in Microbiology, 7 (377) doi: 10.3389/fmicb.2016.00377

Last modified on Friday, 14 October 2016 19:20
Janet Goins

Dr. Janet Goins is Assistant Director of UCLA's Undergraduate Research Center. She works to provide undergraduate students with research experiences that prepare them for future success in STEM-related careers. Previously, her research focused on the ecological impacts of algal host-virus interactions, the evolution of and molecular steps involved in host cell pathogen defense, and the biological factors that influence harmful algal blooms. She was awarded a 2012-2013 ASM-BWF Science Teaching Fellowship and completed its program. In 2015 she received the ASM Science Communication and Strategic Marketing Fellowship.