As it turns out, the holes in Swiss cheese may be from hay particles found in milk, say Swiss scientists. Also, scientists in California have developed a diet drug called Fexaramine, which may trick the digestive system into burning fat without food. Read more
“Fermenting yeasts produce more than just ethanol and carbon dioxide. They make flavorful, aromatic molecules: acids and esters. But which ones make which ones?” wonders William Bostwick as he attempts to recreate a sour beer in his kitchen in San Francisco’s Mission District. If you’re more interested in preventing your beer from getting skunky than making your own, we found some chemistry to help you out.
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Researchers at the American Academy of Microbiology answer the FAQs of cheese-making and Carl Friedrich Gauss, a famous 19th century mathematician, explains the best way to hold a pizza slice–using math, of course.
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Pampered and happy yeast and the perfect beer foam yields delicious beer (and happy beer drinkers).
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Microbes–they’re everywhere! While scientists at the University of Colorado take an inventory of the microorganisms that live on the fruits and vegetables we eat, soil scientists are discovering the link between microorganisms that live in the soil and human health.
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Last month, the third installment of MAD took place in Copenhagen, Denmark. MAD—Danish for “food”—is an annual symposium that brings together world renowned chefs, scientists, writers, and other notable luminaries to discuss and share stories about all things food-related. Hosted by Rene Redzepi and the MAD and noma team and co-curated by Momofuku’s David Chang and Lucky Peach magazine, this year’s symposium focused on “guts,” both in a literal and metaphorical sense. Here are ten things (among many!) we learned from our visit to MAD 2013: Read more
Rachel Dutton is a Bauer fellow at Harvard University where she uses cheese to study microbial ecosystems. She has collaborated with chefs David Chang and Dan Felder of Momofuku, and her research has been featured in Lucky Peach Magazine, The Boston Globe, NPR, The New York Times, and on the PBS TV series Mind of a Chef.
Have you ever been offered a fancy cheese that smelled more like a used gym sock than something edible? Odor artist Sissel Tolaas and researcher Christina Agapakis took this idea and ran with it, with their project Synthetic Aesthetics. The duo used bacteria isolated from human hands, feet, noses, and armpits to generate cheese!
Many cheeses, like beer, wine, and yogurt, are the product of fermentation. Fermentation occurs when microorganisms such as yeast and bacteria convert carbohydrates such as sugar into alcohols, gasses, and acids to generate energy in the absence of oxygen. One common cheese-making type of bacterium, Lactobacillus, breaks down lactose, the primary milk sugar, to lactic acid. This results in lowering the pH of the milk, which as pointed out in a previous post, causes coagulation and solidification into cheese. The work of microorganisms in cheese also results in the creation of many other byproducts that give cheeses their unique smell, texture, and flavor profiles. For example, the bacterium, Propionibacterium freudenreichii, generates carbon dioxide gas in the process of making swiss cheese and causes its characteristic holes [1]. Penicillium roqueforti, which is related to the fungus that helps produce the antibiotic, penicillin, gives blue cheese it’s distinct aroma and look [1].
Microorganisms that use fermentation are found everywhere. Tolaas and Agapakis realized that the human body shared many characteristics with the environments for creating cheese. On a hot day or before a hot date, your armpits may be just as warm and moist as an industrial cheese incubator. Furthermore, cheese-making bacteria like Lactobacillus are common inhabitants in the mammalian gut [1]. With this information, they isolated bacteria from hands, feet, noses, and armpits and added them to whole milk to serve as starter cultures.
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| Figure 1. (A) Swabs from various human body parts incubating in raw milk. (B) Cheeses after solidifying. While no cheeses were consumed, they were evaluated with an odor survey and by DNA sequencing to identify the bacteria cultures present in each cheese. |
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| Figure 2. Samples prepped for the smell survey. Participants of the survey were asked to smell the samples and provide a description of the odors they detected. |
Here are the results:
| Source | Bacteria | Isolated Odors |
| Hand-1 | Providencia vermicola Morganella morganii Proteus mirabilis |
yeast, ocean salt, sour old cheese, feet |
| Foot-1 | Providencia vermicola Morganella morganii Proteus mirabilis |
sweat, big toe nail, cat feet, sweet, milky, orange juice in the fridge too long, fungus, buttery cheese, soapy, light perfume |
| Armpit-1 | Providencia vermicola Morganella morganii Proteus mirabilis |
Feta cheese, Turkish shop, nutty, fruity, fishy |
| Nose-2 | Providencia vermicola Morganella morganii Proteus mirabilis |
cheesy feet, cow, cheese factory, old subway station, toilet cleaner |
| Armpit-2 | Enterococcus faecalis Hafnia alvei |
neutral, perfumed, industrial, synthetic, fermentation, car pollution, burning, sharp, chemical |
| Armpit-3 | Micobacterium lactium Enterococcus faecalis Bacillus pumilus Bacillus clausii |
neutral, sour, floral, smooth, yogurt |
| Foot-5 | Providencia vermicola Proteus mirabilis |
yeast, jam, feet, putrid, sour, rotten |
| Armpit-4 | Enterococcus faecalis | yogurt, sour, fresh cream, butter, whey |
The cheeses displayed a diverse range of bacterial species and odors. Interestingly while some cheeses smelled like “old subway station” or “cat feet,” others exuded the familiar & appetizing flavors of “yogurt,” “feta cheese,” and “light perfume.” Furthermore, some of the bacteria isolated were common to various cheeses. For example, Enterococcus faecalis is a lactic acid bacterium found in raw milk and cheeses, like farmhouse cheddar varieties [2]. Proteus mirabilis is related to Proteus vulgaris, which is responsible for giving surface-ripened cheeses like Limburger and Munster a strong aroma [3].
While these bacterial cultures may not serve as the basis of a new type of artisan cheese, Agapakis notes:
“These cheeses are scientific as well as artistic objects, challenging us to rethink our relationship with our bacteria and with our biotechnology. . . . The cross-over between bacteria found on cheese and on human skin offers a tantalizing hint at how our bacterial symbiotes have come to be part of our culinary cultures.”
In the face of diminishing resources, we are reminded that untapped reservoirs, which may be literally under our noses, might contain hidden treasures that could change the way we generate and produce food.
Online Resources
References cited
About the author: Vince C Reyes earned his Ph.D. in Civil Engineering at UCLA. Vince loves to explore the deliciousness of all things edible.
The momofuku team, led by chef/owner David Chang, swung through town during our week on microbes. David Chang and Peter Meehan produce the literary magazine Lucky Peach. Dan Felder and Veronica Trevizo are chefs who work in the momofuku kitchen lab. For LA Weekly’s rundown of the public lecture, see here. For more photos, see here.
momofuku chef Dan Felder before class begins
Microbial fermentation is one of the oldest cooking techniques in the world. In the past two years, the momofuku team has been working to understand fermentation and apply it in innovative ways. When the team visited, we first tasted pistachio miso and MSG. Miso is traditionally made by inoculating soybeans or barley with Aspergillus oryzae, or koji in Japanese. Koji is a mold that is also used in making sake and soy sauce. The momofuku team took this idea a step further, experimenting with inoculating untraditional ingredients with A. oryzae. The resultant pistachio miso is a mildly salty paste with a subtle note of the nut. It tastes like dou fu ru, a fermented bean curd from China, of which, incidentally, some varieties are also made with A. oryzae.
The momofuku team took this pistachio miso another step further, by centrifuging it. The miso separated into 4 layers, one of which is the “pistachio tamari” pictured below. We also sampled cherry and rhubarb vinegars from the lab.
In making these fermentation products themselves, the momofuku chefs are putting an American spin on foreign products. Yes, they are Japanese in tradition, but they are made with a unique microbial community that is found nowhere else in the world except at 10th St and First Avenue in NYC. A deeper knowledge of science is valuable not only for understanding how each step of fermentation modifies the flavor and texture of the ingredients, it is also vital for safety. For a couple of years now, the chefs have been working with our friends Rachel Dutton and Ben Wolfe at Harvard who identify the microbes on momofuku samples and let the team know whether it is safe to eat them.
Further reading:
Felder, Dan, et al. “Defining microbial terroir: The use of native fungi for the study of traditional fermentative processes.” International Journal of Gastronomy and Food Science. 1.1 (2012): 64-69.
Speaking of letting things rot, see here to learn more about artist Heike Leis’ photographs of food rotting way beyond edibility.
In our unit on microbes and exponential growth, we learned about the role of microbes in altering flavor and mouthfeel. One of our favorite microbial foods is cheese: Cheese would just be spoiled milk if it were not for microbes.
To kick off the class, we challenged the students with a taste test featuring four distinct cheeses:
A) Amish Blue Wheel
B) Emmental
C) Cheddar
D) Port du Salut
We also presented four different types of microbes, and a bit about natural habitats. Can you guess which microbe belongs to which cheese? Answers below.
1) Propionibacterium (inhabit human skin)
2) Penicillium mold (grow in cool, moderate climate; some species have blue color)
3) Brevibacterium (grow especially well without much personal hygeine)
4) Lactococcus lactis (grow well in acidic conditions)
ANSWERS:
A. 2 – Blue cheeses are inoculated with a strain of Penicillium mold, Penicillium roqueforti. Needles or skewers are used during the inoculation, which is why blue cheeses often have distinct veins running through them.
B. 1 – Emmental is a type of Swiss cheese, which is known for its holes. These holes are bubbles excavated by carbon dioxide, a byproduct of lipid breakdown by Propionibacterium freudenreichii, subsp shermanii. Its close cousin, Propionibacterium acnes, is linked to acne.
C. 4 – Cheddar is an example of a wide variety of cheese types that rely on Lactococcus lactis for the first stage of ripening. L. lactis uses enzymes to produce energy from lactose, a sugar molecule common in dairy products. Lactic acid is the byproduct.
D. 3 – Port du Salut is a washed-rind cheese. The cheese surface is wiped or washed down with a brine that promotes the growth of certain bacteria in the air. A smear of bacteria can be directly applied to the surface to nudge along the process. Brevibacteria linens is commonly used during this inoculation. Ever get a whiff of stinky feet from your cheese? Brevibacteria linens is the culprit, in the cheese and on real smelly feet.