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ISAPP discussion group leads to new review paper providing a global perspective on the science of fermented foods and beverages

By Kristina Campbell, MSc, Science & Medical Writer

Despite the huge variety of fermented foods that have originated in countries all over the world, there are relatively few published studies describing the microbiological similarities and differences between these very diverse foods and beverages. But in recent years, thanks to the availability of high throughput sequencing and other molecular technologies combined with new computational tools, analyses of the microbes that transform fresh substrates into fermented foods are becoming more frequent.

A group of researchers from North America, Europe, and Asia gathered at the International Scientific Association for Probiotics and Prebiotics (ISAPP) 2018 conference in Singapore to discuss the science of fermented foods. Their goal was to provide a global perspective on fermented foods to account for the many  cultural, technological, and microbiological differences between east and west. This expert panel discussion culminated in a new review paper, published in Comprehensive Reviews in Food Science and Food Safety, entitled Fermented foods in a global age: East meets West.

Prof. Robert Hutkins, the paper’s lead author, says the diversity of panelists in the discussion group was an important aspect of this work. “Although we were all connected by our shared interests in fermented foods, each panelist brought a particular expertise along with different cultural backgrounds to our discussions,” he says. “Thus, one of the important outcomes, as noted in the published review paper, was how greatly historical and cultural factors, apart from microbiology, influence the types of fermented foods and beverages consumed around the world.”

The review captures the current state of knowledge on the variety of microbes that create fermented foods: whether these are starter cultures or microbes already present in the surrounding environment (i.e. the ‘authochthonous’ or ‘indigenous’ microbiota). The paper identifies general region-specific differences in the preparation of fermented foods, and the contrast between traditional and modern production of fermented foods—including the trade-offs between local and larger-scale manufacturing.

The authors of the article also took on the painstaking work of cataloging dozens of fermented foods from all over the world, including fermented milk products, fermented cereal foods, fermented vegetable products, fermented legume foods, fermented root crop foods, fermented meat foods, fermented fish products, and alcoholic beverages.

The expert panel discussions held every year at the ISAPP annual meeting provide a much-anticipated opportunity for globally leading scientists to come together to discuss issues relevant to scientific innovation and the direction of the field. This paper is an example of a concrete outcome of one of these discussion groups.

For more on fermented foods, see this ISAPP infographic or this educational video.

Maintaining a family tradition: Bulgarian whole fermented cabbage

By Mariya Petrova, PhD, Microbiome insights and Probiotics Consultancy, Karlovo, Bulgaria

Dr. Mariya Petrova with her father

November and December mark a wonderful time of the year when the cold weather makes you want to stay at home and enjoy homemade foods and drinks. However, the heavy food during the holidays makes all of us think about healthier alternatives and how to keep our gut microbiomes in check. That’s why it can be great idea to supplement your festive menu with fermented foods.

Cabbage ready to be fermented

Partly to have healthier food options at home and partly to engage in longstanding traditions, at this time of the year, millions of people in Eastern Europe roll up their sleeves, get out their knives, salt and large containers, and make fermented vegetables at home. While Western cultures are seeing fermented foods as a trendy health food option, Eastern Europeans have never forgotten how to preserve food by using natural fermentation. In my country of Bulgaria, fermented foods are simply a part of our life. Our most popular fermented foods include whole sour cabbage, pickles and pickled vegetables, yogurt, boza (a special fermented beverage), and fermented apple cider vinegar. We do not take shortcuts by pickling our vegetables with vinegar. Ours is a traditional fermentation process – add salt and then let the natural lactic acid bacteria perform their magic.

Although all of these products are interesting and delicious, the winter season brings to my mind my father’s whole cabbage fermentation. My father is busy with it every year from the beginning of November until mid-December. Whole sour cabbage is a fermented food popular not only in Bulgaria but in many of our neighboring countries such as Serbia, Macedonia, and Romania. Although similar to sauerkraut, Bulgarian whole fermented cabbage ferments the entire cabbage head, not separate cut or shredded leaves. Using whole cabbage requires both an extended period of fermentation time (around 30 to 40 days) and extra care in handling.

Preparing for fermentation

I have pictures etched in my mind of a busy local Saturday vegetable market where people would buy between 30-50 kilograms (sometimes even more) of cabbages for fermentation – depending on the size of their families. These come to life every time I hear “fermented foods” at a conference!

Cabbage and brine

But how do you ferment such a spectacular amount of cabbage? Well, first you need some rather large barrels, of course. Then you remove the outer leaves from the cabbage, core the cabbage heads, and stick them in the barrel. This is not unlike putting together a jigsaw puzzle. The cabbage heads have to be very dense without leaving to much space between them or the fermentation will not work well. The cabbage is then covered with a brine of around 2-4% salt. Finally, something heavy is placed on top of the cabbage. Many people place a heavy rock (clean of course), to keep the cabbage heads under the salty water and to allow them to ferment properly. Packing the cabbage densely and pressing it down is done to reduce oxygen to a minimum, creating an anaerobic environment for the fermentation. For better taste some people optionally add apple, quince, horseradish, and/or beetroot (which also makes the salty water more pink).

Finished fermented cabbage

Every day the salty water has to be inverted which is achieved by flushing it from the bottom of the barrel by using connected vessels and then adding it onto the top. Day-to-day shuffling of the salty water ensures a uniform distribution of microorganisms in the barrel so that all cabbage heads ferment. The best quality fermented cabbage is produced at 12-18°C temperature for around 30 days. This is why the fermentation

is done only in November – to maintain these low temperatures. Temperature from 7.5 to 18°C favors the growth and metabolism of Leuconostoc mesenteroides, while temperatures higher than 20°C favor the growth of Lactobacillus species. At higher temperatures the fermentation process takes shorter time (around 10 days), but the quality of the fermented cabbage is lower. Leuconostoc mesenteroides is essential to start the first fermentation that produces lactic acid, acetic acid, ethyl alcohol, carbon dioxide, and mannitol. All these acids, in combination with aromatic ester alcohol, contribute to the characteristic taste of high-quality sour cabbage.

Following Leuconostoc mesenteroides fermentation, Lactobacillus plantarum takes over lactic acid production, which gives a sour taste to the fermented cabbage. At the end of this Lactobacillus fermentation the cabbage is ready to enjoy as part of traditional Bulgarian cuisine. Like a special gift left by St. Nick, many people use the salted water in which the cabbage was fermenting as a drink, rich in lactic acid bacteria, and said to help digestive health.

Acknowledgment: I thank my father for showing me how to make the fermented cabbage and taking some pictures of the process this year!

Fermented foods on the holiday dinner table

Bacteria illustration

Suggestions for Making Safe Fermented Foods at Home

September 2017 – By Drs. Bruno Pot and Frédéric Leroy, Vrije Universiteit Brussels, Brussels, Belgium.

The impact of lifestyle on the composition and diversity of the human gut microbiota over the last five decades has been tremendous. This is thought to be mainly the result of a cumulative effect ascribed to the increased use of antibiotics and other drugs as well as dietary changes, including consuming less fermented foods that contain live microorganisms.

Fermented foods are important for a healthy diet, as they have the potential to improve the microbiota quality and diversity, are related with reduced disease risk, and can provide essential nutrients.  Consumers are constantly being informed about these benefits, leading to pleas for a return to home-made fermented foods. However, there is rarely mention of the risks that home-made natural fermentations can entail. While making fermented foods at home can be a good idea and help you consume more beneficial microbes, we should realize that the empirical knowhow, skills and equipment to make safe food fermentations may have disappeared over time. This blog is a gentle warning about the possible risks of non-controlled fermentations.

  • Use a starter culture: The use of specific starter cultures at sufficiently high concentration is recommended to properly initiate the fermentation of specific foods and to obtain sufficient control over the process. Relying on spontaneous fermentation (i.e., hoping that environmental bacteria or yeasts initiate the fermentation) increases the risk that uncontrolled fermentations by unsuitable bacteria, yeasts and molds will result in bad or variable quality. In the worst case, dangerous end-products will be obtained.
  • Twice is nice: Starters should not be used repeatedly. Because bacteria multiply several times per hour, their genetic material is changing continuously and the quality of the starter will change over time. It is therefore not a good idea to re-use your ‘old’ product to restart a ‘new’ fermentation all too often, although some fermented food ecosystems such as sourdough or water kefir may usually be ‘backslopped’ frequently. The risks are that off-flavours will be formed or that acidification, which protects your food against the growth of spoilage or pathogenic bacteria, will be too slow.
  • Choose wisely: Not all starters are necessarily safe, although commercially available ones should in principle have been checked for safety (See Helpful Information links below for guidance on findings the right starter). Some yeasts and lactic acid bacteria (LAB) can form compounds (for example, biogenic amines from amino acids) that can result in many health troubles like headache, blood pressure drops, diarrhoea, and even heart problems. You can avoid the production of biogenic amines by using selected starters that do not have the metabolic machinery to make them.
  • To breathe or not to breathe: Some fermentations, like the production of water kefir (usually using dried figs), should be performed in the absence of air and thus require a rubber sealing. For other fermentations, a complete submerging in brine or a covering with oil is necessary. Kombucha, on the contrary, needs a wide opening covered by a cloth that allows oxygen into the vessel. Uncontrolled anaerobic conditions can increase the risk for the growth of clostridia. In cheese making they can be the cause of cheese blowing up, in other conditions they may produce the deadly botulin toxin.
  • Avoid Moulds. Moulds are another problem linked to (too much) oxygen. Moulds can make mycotoxins which can make one very sick and any visible contamination should ring bells! It is not wise to scrape them off, as often they have produced toxins already, left spores or will remain present through their ‘roots’ which most of the time are not visible.
  • Hold the alcohol: During fermentation, sugars are converted to lactic and acetic acids, but also to ethanol. Therefore, the concentration of sugar added may impact the final alcohol levels of the end-product.
  • Pass the gas: In the case of water kefir, the use of a water lock can be necessary, as the CO2 gas which is formed during the fermentation may increase the pressure in the vessel, leading to potential breaking or surprises during opening. Therefore, blown fermented foods products should never be consumed.
  • Party crashers and acid balance: Not all bacteria are your friends. Some undesirables can be present on fresh vegetable products and can in themselves lead to spontaneous fermentation. Therefore, it is important to not let your fermentation be hijacked by these bacteria. The good bacteria should grow and produce acid quickly for a safe fermentation. Pathogens generally cannot grow in high acid environments (below pH 4 is a safe target). This acidity should be reached as quickly as possible during fermentation to avoid the growth of bacteria which can produce toxins or off flavours.
  • Nothing lasts forever: While high acid is essential, it does not protect the food indefinitely. Some yeasts and fungi can grow in high acid. As they grow, some can reduce acidity locally so that (mainly at the surface) other (potentially pathogenic) bacteria can develop
  • Use good quality raw materials. Use only good quality and fresh ingredients when deciding to ferment. While fermentation helps to preserve your fresh foods longer, it will not rescue (almost) spoiled products!
  • Summer and winter milk. If you use milk in your fermentation, it is also possible that the quality of the end product will be different along with the season, as summer milk, harvested from cows in the field, has a different composition from milk harvested from cows fed winterfeed.
  • Temperature. Temperature control is important. While for sauerkraut room temperature 18-22 (65-72°F) is fine, yoghurt fermentation is much better at 37°C (100°F). You, therefore, can expect differences in summer and winter if you do not control the temperature. Find the right spot in the house for both summer and winter.
  • Water activity. In addition to acidification, microbial control is often achieved by reduction of the water activity, generally by sufficient salting and/or drying. This is of major importance to produce fermented sausages. It is important to point out that raw meat is a particularly hazardous matrix, requiring even more care and attention when performed at home.
  • Salt and acetic acid (vinegar) concentration. Both ingredients help keep the pathogens at bay. Stick to recipes that have proven to be reliable.
  • Fermentation time. This is an important factor which can vary a lot and, in turn, impact the quality of your end product. Its critical nature is well known from wine making, in which the duration of the primary and secondary fermentation is well known to be crucial to the quality of the result. While in wine the primary fermentation usually takes between 3 to 7 days, the secondary fermentation can take much longer and will depend on the vial, the alcohol concentration and the yeast used. The fermentation of sauerkraut goes in three stages. ALL three are essential for a safe and tasteful product; a minimum of three to four weeks is necessary. Industrially produced yoghurt can be made in 8 hours, but at home it may take a few hours more. How much more again depends on the milk quality, the starter and the temperature.
  • Do’s and don’t’s: Do invest in a kitchen weighing scale and a thermometer that goes from 0 – 100 °C. Don’t even think about home-made sausage.  Don’t even think about raw-milk cheese.  Do start with simple foods like yogurt or kefir.  There are fool-proof kits for making beer (although they require some hardware).  Sauerkraut and kimchi are relatively easy to make.

Being aware of these simple concepts can help ensure the production of a healthy, tasty fermented food. Consumers should expect that the quality of the resulting fermented food will vary from lot to lot and they should be able to judge when a product is still safe for consumption and when it is not. Consumers should also be aware of the risk factors above and know how to select and handle equipment and execute procedures that will yield safe and nutritious end products.

For additional information:

Fermented Foods on the www.ISAPPscience.org website.

Preparing Fermented Foods and Pickled Vegetables

The University of Georgia Cooperative Extension, the National Center for Home Food Preservation

Safe Preserving: Fermented Foods From the University of Wisconsin Extension