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Sauerkraut

 

Photo credit: Flickr user cmbellman

Photo credit: Anders Adermark (cmbellman/Flickr)

Fizzy, bitter, yeasty, sour, floral, and sometimes just downright offensive—there are a dazzling array of adjectives that can come to mind when you think of fermentation. Fermentation is one of world’s oldest and simplest culinary traditions. Serendipitously discovered in ancient times as a means of preservation, flavor enhancement, and intoxication, it has exploded as an art and scientific field in recent years. Aptly described by Chef David Chang as when “rotten goes right,” fermentation is a process that harnesses the power of benign microbes to produce complex flavors and can transform a seemingly rotten pile of vegetables into a curiously palatable delight (1). It’s fermentation we can thank for transforming a lonely, simple cabbage into a bustling hotspot for microbial activity that we know as sauerkraut.

German for “sour cabbage,” sauerkraut is distinctively tangy, floral, and surprisingly simple to create. It requires no specialized ingredients or starters, demanding just cabbage and salt (1). Sauerkraut is an example of wild fermentation, a process that exploits microbes native to the surface of cabbages. To make a batch, begin with finely shredded cabbage with roughly 3 tbsp salt per 5 lbs of cabbage. Give your fingers a workout by gently massaging the cabbage mix and after a few minutes, you’ll notice that the cabbage appears to be sweating (2). This sweat is the basis for our brine, whose presence is absolutely vital in our cabbage-to-sauerkraut transformation.

This brine sets a stage for successful sauerkraut fermentation, a fermentation made possible by the flavorful collaboration between several different microbes. These microbes, specifically lactic acid bacteria and yeast, thrive in salty, anaerobic environments, much like in the brine (1). Although the brine is simple, comprising just salt and water, it must be carefully controlled so as to provide the lactic acid bacteria and yeasts with a competitive advantage over other undesirable organisms. Too much salt and you ruin the palatability of our sauerkraut, but too little salt and you risk creating an environment favorable to spoilage or pathogenic bacteria (3).

As the microbes feed on sugars in cabbage, they mainly produce lactic acid, which like salt lends taste in addition to antimicrobial effects. As the brine becomes enriched with lactic acid, the pH declines and the sauerkraut begins to develop tart notes. These effects inhibit the growth of our unwanted microbes, which tend to be sensitive to acidity. Secondary products can also include carbon dioxide, alcohol, and acetic acid, all of which can suppress the growth of our unwanted organisms, too (3).

After massaging long enough, you should have enough brine to prepare your cabbage for jarring. Employing a willing and eager fist, pack your cabbage into a jar so that it’s completely submerged beneath the recently-created brine—you may also want to consider weighing it down. Ensure that your cabbage is entirely covered by brine, otherwise you risk inviting the growth of harmful aerobic bacteria into your jar. Anything left exposed to air is susceptible to mold or invasion of other organisms (2).

Depending on your preferences, you can let your sauerkraut ferment for just a few days or up to several weeks if you prefer stronger flavors. Leave it in a closet, on your countertop, or bury it in your backyard—it’s totally up to you!

References cited

  1. McGee, Harold. On food and cooking: the science and lore of the kitchen. New York: Scribner, 2004. Print.
  2. Katz, Sandor E. Wild Fermentation: The Flavor, Nutrition, and Craft of Live-Culture Foods. White River Junction, VT: Chelsea Green Pub, 2003. Print.
  3. Katz, Sandor E., Michael Pollan. The Art of Fermentation: An In-Depth Exploration of Essential Concepts and Processes from Around the World. White River Junction, VT: Chelsea Green Pub, 2012. Print.

Mai NguyenAbout the author: Mai Nguyen is an aspiring food scientist who received her B.S. in biochemistry from the University of Virginia. She hopes to soon escape the bench in pursuit of a more creative and fulfilling career.

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The International Year of Pulses

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Photo credits: (flickr/Jessica Spengler)

The 68th United Nations General Assembly has declared 2016 the International Year of Pulses. [1] Pulses – that throbbing sensation of your carotid artery after a workout or during a first date, right? Nope. The UN suggests we celebrate the pulses that are leguminous crops harvested solely for their dry seeds. All lentils, and all varieties of dried beans, such as kidney beans, lima beans, butter beans and broad beans are pulses, as are chick peas, cowpeas, black-eyed peas and pigeon peas. Seeds that are harvested green, like green peas or green beans are classified as vegetable crops, not pulses. Legumes used primarily for oil extraction, like soybeans, are also not pulses. [2]

Why are pulses getting a year-long, world-wide campaign?

A global push for pulse production would address many problems of our global food system. The Food and Agriculture Organization of the United Nations’s campaign highlights these key benefits to pulse cultivation [1]:

  • Pulses are highly nutritious – they are excellent plant source of protein, and contain the B vitamins that our bodies require to convert food to energy
  • Pulses are economically accessible and contribute to food security at all levels – from farmers to consumers
  • Pulses foster sustainable agriculture, thus addressing agriculture’s role in climate change
  • Pulses promote biodiversity in agriculture

 

Now that we know the basics of pulses and why they’re important, let’s get scientific.

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Photo credits: (flickr/Kelly Garbato)

Pulses in the nitrogen cycle

Pulses are legumes, or plants in the family Leguminosae. Thanks to their symbiosis with many members of the diazotrophic, or nitrogen-fixing bacterial genus Rhizobium that live in their roots and feed them with nitrogen from the air, pulses have a particularly high protein content compared to non-legumes. [3] Within the bacterium, atmospheric nitrogen (N2), which is typically unusable to plants, is converted to ammonium (NH4+) via the activity of the enzyme nitrogenase. The nitrogen of ammonium is converted to other more complex compounds that are beneficial to humans, like amino acids – the building blocks of protein. In exchange for fixing nitrogen, the bacterium receives food from the plant — carbon in the form of glucose (C6H12O6).

 

This remarkable bacterial symbiosis also enriches the soil in which pulses grow with nitrogen compounds like nitrite (NO2) and nitrate (NO3), which is the preferred nitrogen source for other green plants. For this reason, farmers who crop-rotate with legumes don’t need to apply nearly as much fertilizer as farmers who don’t. [3]

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Pulses in a changing climate

Many pulses are also hardy and drought tolerant crops – lentils, broad beans, peas, and chick peas are all native to the Fertile Crescent of the Near East, and have adapted to sprout quickly and reproduce in the rainy season before the hot, dry summer [3].

Anatomy of the pulse

All food seeds consist of three basic parts: an outer protective coat, the small embryonic portion that develops into the mature plant, and the storage tissue that feeds the plant embryo. [3]The bulk of the seed consists of storage cells are filled with particles of concentrated protein and granules of starch, or organized masses of starch chains.

Cooking and starch retrogradation

When we cook pulses, hot water permeates the starch granules. As the water molecules work themselves between the starch chains, the granules swell and soften. When the pulses later cool down, the starch chains bond to each other again in tighter, more organized associations, resulting in firmer granules. (This process is called retrogradation.) [3] Consider leftover lentils or beans: they’re always harder and drier the next day, and they never get quite as soft as when they were first cooked. This is because during the process of retrogradation, some starch molecules form granules that are even more tightly associated than the bonds in the original starch granule. They form small crystalline regions that resist breaking even at boiling temperatures. [3]

Retrogradation of starch might foil your plans for leftover lentils, but it does do our bodies good: Our digestive enzymes cannot easily digest retrograded starch, so eating it results in a more gradual rise in blood sugar compared to the effects of non-retrograded starch. [3] Our intestines need help breaking down this tough starch, and the beneficial bacteria in our large intestines are happy to be of assistance. Just as the diazotrophic bacteria in soil work in harmony with leguminous plants, our intestinal bacteria digests what we cannot. Thus the retrograded starch functions as a prebiotics, or food for the probiotic bacteria in our guts. Well-fed gut bacteria make for healthy digestive tracks and happy bowels.

Will this pulse promotion save the world and fix the global food economy? Perhaps. We can all do our part by making a hearty spinach dal for dinner tonight, and sweet red bean paste for dessert.

 

Works Cited

  1. “”Save and Grow in Practice” Highlights Importance of Pulses in Crop Rotations and Intercropping.” Pulses – 2016 | 2016 International Year of Pulses. Food and Agriculture Organization of the United Nations, n.d. Web. 05 Feb. 2016.
  2. “What Are Pulses? | FAO.” What Are Pulses? | FAO. Food and Agriculture Organization of the United Nations, 15 Oct. 2015. Web. 05 Feb. 2016.
  3. McGee, Harold. “Seeds.” On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner, 2004. N. pag. Print.

Elsbeth SitesAbout the author: Elsbeth Sites received her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

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10 Things We Learned at MAD 2013

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

Human Cheese

Cheese1

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.

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.
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

  1. More about this project
  2. More about Christina Agapakis
  3. More about Sissel Tolaas
  4. More about bacteria found on the human body
  5. More about the basics of cheese making


References cited

  1. Agapakis, C. 2011. Human Cultures and Microbial Ecosystems. http://agapakis.com/cheese.pdf
  2. Gelsomino. R. et al. 2002. Sources of Enterococci in Farmhouse Raw-Milk Cheese. Applied and Environmental Microbiology 68(7): 3560-3565.
  3. Deetae. P. et al. 2009. Effects of Proteus vulgaris growth on the establishment of a cheese microbial community and on the production of volatile aroma compounds in a model cheese. Journal of Applied Microbiology 107(4):1404-1413.

Vince ReyesAbout the author: Vince C Reyes earned his Ph.D. in Civil Engineering at UCLA. Vince loves to explore the deliciousness of all things edible.

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Does your cheese taste of microbes?

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.