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Summary
We tend to forget that most microbes, which make up more than two-thirds of the world’s biomass, are harmless - or even helpful - to us. Without microbes, for example, our holiday menus would look dramatically different… and not for the better! The key is fermentation, which doesn’t sound particularly appetizing but is responsible for making – usually under carefully controlled conditions and with painstakingly selected cultures - many of our dietary staples and delicacies. Production of cheese (and a host of other dairy products), wine, beer, olives and even chocolate require microbe-induced fermentation.
16 December 2008 Dr. Kristen Kerksiek
We wish you a Merry Microbe!
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“On the first day of Christmas, my true love sent to me
A partridge in a pear tree…"
(The Twelve Days of Christmas, Traditional English Carol)
This standard English Christmas song dates from the Middle Ages, when birds were a fundamental part of the celebratory banquets of Christmas. Many of us still enjoy goose, turkey or duck as part of our holiday feast. However, the tongue-tingling indulgences of the holiday season extend far beyond the bird. And many of our celebratory staples, from chocolate Santas to mulled wine (Glühwein), butter cookies to Raclette, wouldn’t exist without help from….yes, microbes!
For thousands of years, microbes have influenced the human diet by causing fermentation, the conversion of carbohydrates into alcohols or acids. Natural fermentation caused by “tasty” microbes not only changes the smell, taste and texture of foods, it also prevents the growth of “nasty” microbes, making it safer to store foods. However, the production of alcoholic drinks, dairy products and bread by our ancestors was sometimes a hit-and-miss process; for example, the wild yeast that lands in juice can produce a high-quality, unique-tasting wine or something more akin to vinegar. Microbes remained unappreciated as food “producers” until the mid-19th century, when Louis Pasteur made the connection between yeast and fermentation. Since then we’ve gained a relatively good understanding of microbes and fermentation, enabling tight control of the process from start to finish and selection of ideal properties through use of special cultures of microbes.
What shall we give the Beloved of Mary?
What can we give to her Beautiful Child?
Raisins and olives and nutmeats and honey,
Candy and figs and some cheese that is mild.
(The Son of Mary/El Noi de la Mare, traditional Catalonian Carol)
Fermentation of dairy products has been performed for centuries and is the most common exploitation of bacteria in food preparation. Before anything was known about lactic acid bacteria, which metabolize the milk sugar lactose into lactic acid, humans were aware that a new batch yogurt, cheese & Co. could be made using “starter” from the last batch. Now we know the specific bacteria involved in these processes and can give them the credit they deserve!
Cheese fondue, Cheese balls, Cheese plates, Cheese and wine…Cheese, glorious cheese! This dietary – and celebratory - staple varies in flavor, texture and appearance based on microbial activity at different stages during its manufacture. Starter cultures (often Lactococcus lactis, Streptococcus salivarius subsp. thermophilus, Lactobacillus delbrueckii and Lactobacillus helveticus) used early in the cheese-making process assist with coagulation, provide flavor and help prevent the growth of “nasty” microbes. Additional (adjunct) cultures are often added for flavor or texture (e.g. the holes in Swiss cheese created by Propionibacterium freudenreichii or shermanii) and are even used to form the characteristic rinds of some cheeses (Brevibacterium linens of Romadur and Limburger cheeses).
Molds also make a significant contribution to the production of a number of cheeses. Originally a natural contaminant, Penicillium roqueforti adds the blue veins of Stilton and Roquefort, and its relative Penicillium camemberti is added to the surface of Camembert and Brie.
Cheese does not stand alone among dairy products in its relationship with the microbial world; yogurt, buttermilk, sour cream and butter are only some of the additional dairy foods produced using fermentation. But it’s time leave the world of dairy and appreciate some of the other delectable treats that microbes enable us to enjoy.
(By the way, olives – also mentioned in the song above – are edible only after fermentation with Lactobacillus plantarum and Lactobacillus mesenteroides)
Wassail! wassail! all over the town,
Our toast it is white and our ale it is brown;
Our bowl it is made of the good maple tree;
With the wassailing bowl, we'll drink to thee.
(Gloucestershire Wassail, 18th Century English Carol)
It must be worth singing about! Wassailing songs, or songs about the traditions surrounding wassail, are among the most popular of the secular (non-religious) holiday songs of Christmas. Wassail has come to refer to a spiced punch, but historical wassail was a mulled (sweetened and spiced) beer or mead, a close relative to the mulled wine that is an almost inseparable part of German Christmas markets and the “theme” of parties held throughout Scandinavia in the weeks before Christmas. Whether it’s called Glühwein, Glögg, Gløgg, vin chaud or vin brulé – it’s hard for many Europeans to imagine the holidays without it.
Wine and beer result from the fermentation of grape juice and cereals (most commonly malted barley), respectively. They are among the world’s oldest beverages, with production possibly dating as far back as 6000 BC. Given the unpredictable outcome of fermentation with naturally occurring microbes, it could be that the sweetened and spiced versions we warm ourselves with today were developed to “rescue” suboptimal production; the idea isn’t new, a tankard for Glühwein was documented almost 600 years ago (1420). Production today is of course highly controlled, with careful addition of the optimal cultures of yeast.
There are thousands of strains of yeast used in the production of beer today, almost all belonging to the ale-producing Saccharomyces cerevisiae (also used for the production of bread) or lager-producing Saccharomyces carlsbergensis. Top-fermenting S. cerevisiae work at relatively high temperatures (16°C–25°C), while bottom-fermenting S. carlsbergensis species function at lower temperatures (4°C–9°C). There are two deviants among beers: Torulaspora delbrueckii (also known as Saccharomyces delbrueckii or Saccharomyces rosei) is used in brewing German-style wheat beers, and the Belgian Lambic beers are fermented predominantly by Brettanomyces bruxellensis and Brettanomyces lambicus (no cultured organisms are added, and as many as 86 different “wild” yeast and bacteria have been identified).
In wine making, the selection of yeast is a bit more open, with 15 different genera – each providing certain flavor characteristics – represented, from Brettanomyces to Candida and Saccharomyces to Zygosaccharomyces (for more information: Pretorius, I. 2000. Tailoring wine yeast for the new millennium: novel approaches to the ancient art of winemaking. Yeast. 16: 675–729). And a bacterium has its hand in the process, too: by fermenting lactic acid, Oenococcus oeni plays a critical role in de-acidifying wine.
And what would you like with your mulled wine/Glühwein/Gløgg? Perhaps a chocolate-covered Lebkuchen (gingerbread) or a special praline? Why not some marble cake or a chocolate-dipped butter cookie? Mmmmm! Attention chocolate lovers! Without microbes, we – yes, I’m outing myself – would not be able to indulge in our favorite treats.
Twas the night before Christmas, when all through the house
Not a creature was stirring, not even a mouse.
The stockings were hung by the chimney with care,
In hopes that St Nicholas soon would be there.
The children were nestled all snug in their beds,
While visions of sugar plums danced in their heads.
(Twas the night before Christmas, poem written 1822 by Clement Clarke Moore)
Christmas season is chocolate season, and an ode to chocolate would seem appropriate here (sugar plums are small, round, hard candies). But apparently people prefer to savor their chocolate than to sing about it.
The cacao tree has been cultivated for some 3000 years in Mexico and Central America. In both Mayan and Aztec cultures, the seeds – some 30-40 in each pod – were crushed to make a highly valued chocolate drink and were even used as currency. But if used directly from the tree, cacao seeds are not only bitter, they don’t taste anything like chocolate. The chocolate flavor develops through fermentation. And this is a process scientists haven’t been able to get a real handle on (no specially selected microbial cultures here!).
The cacao pods, consisting of seeds and the sweet, sticky goop that surrounds them, are split open with a hammer or machete, thrown in a pile and covered with banana leaves. They are left for 5-7 days (turned daily to let in air) to undergo a complex fermentation process that involves a succession of naturally occurring microbes. The yeasts start, with at least 11 different species (Saccharomyces cerevisiae, Candida rugosa, and Kluyveromyces marxianus…) identified in the brew. Then come over 30 species of bacteria, starting with lactic acid bacteria (e.g. Lactobacillus and Streptococcus) followed by acetic acid bacteria (e.g. Acetobacter and Gluconobacter) and some endospore-forming rods. Filamentous fungi round out the fermentation process during which alcohols, acids and heat induce biochemical changes inside the beans. Changes all chocolate lovers can be very thankful for!
We wish you a Merry Christmas, We wish you a Merry Christmas,
We wish you a Merry Christmas, and a Happy New Year
Good tidings to you wherever you are;
Good tidings for Christmas and a Happy New Year!
“Tasty” microbes impact our lives daily, usually without any recognition at all. Some are involved directly in food production (only the tip of the iceberg is mentioned here!), while others are used to produce vitamins, enzymes, amino acids and other non-food products. Perhaps this year while we’re savoring our holiday treats and feasts, we can reserve a little thought – and thanks – for the bugs that have made it possible.
For more details about The Microbiology of Chocolate, see http://www.smccd.net/accounts/case/chocolate.html