Have you ever wondered how some foods like sauerkraut or yogurt last so long without spoiling? The answer lies in a fascinating process called fermentation, powered by tiny microbes! In this second post of the Fermented Foods Series, we’ll delve into the world of fermented foods, exploring what they are, the microbes behind the magic, and why you might want to try making your own at home.
Fermented foods are not just delicious and tangy, they’re also packed with potential health benefits. Plus, making your own fermented foods is a fun and rewarding experience! But with all the buzz about fermentation, there can be confusion and even fear about safety. This post will address those concerns and equip you with the knowledge to ferment safely at home.
So, buckle up and get ready to learn about fermented foods, the microbes that make them possible, the fun of DIY fermentation, and some essential safety tips. We’ll cover popular fermented foods like sauerkraut, kombucha, and kefir, and explore the exciting world of these tasty and potentially health-boosting creations.
What are fermented foods?
Fermented foods are foods that have been transformed by the action of fermentation. Fermentation occurs when microbes take sugars and turn them into various products like acetic acid, lactic acid, alcohol (ethanol), and carbon dioxide gas.
Another way to put it is fermentation is “the microbial transformation of a food in order to extend the shelf life, improve the taste of it, or add beneficial properties, such as health-promoting properties, through microbial action,” says John Leech, a 3rd year PhD student who studies fermented foods in Dr. Paul Cotter’s lab.
Beer, wine, sourdough bread, sauerkraut, kombucha, yogurt, and kefir are just a few of the many delicious fermented foods people enjoy.
Recently, a lot of the conversations about fermented foods have been centered around the potential health benefits, which I will cover in the next blog post. But, as Leech says, fermentation can extend the shelf life of foods and therefore be used to preserve food. This ability to preserve food is especially useful for vegetables and fruits, which go bad quickly. Thus fermentation can help alleviate this issue.
But if microbes are involved, where do they come from?
There are two ways to start the fermentation process with microbes:
1) With a starter culture – microbes are specifically added to the food do the fermentation
2) Through spontaneous or wild fermentation – microbes present on/in the food and/or the environment do the fermentation
What types of microbes do the fermenting?
Fermentation can occur spontaneously or you can start the process with a starter culture of microbes. But what types of microbes are we talking about? The simple answer is that it depends on the food.
Yeast is responsible for many of the most well-known fermented foods: bread, beer, and wine.
Lactic acid bacteria are responsible for fermented milk products such as yogurt and cultured butter.
Some fermented foods are a product of the combined efforts of bacteria and yeast, which can sometimes be achieved by a “scoby” or a Symbiotic Culture Of Bacteria and Yeast, including water and milk kefir and kombucha.
So, many different microbes can be involved, depending on the substrate (food).
What types of foods can we ferment?
You can ferment vegetables, fruits, milk, and almost any kind of food, as long as it contains sugar. But some foods are more common to ferment than others.
The list below mostly includes the foods that were mentioned throughout the interviews I conducted.
| Food/Substrate | Fermented Food Product |
| Cabbage | Sauerkraut, Kimchi |
| Milk | Yogurt, Milk Kefir, Viili |
| Sugar Water | Water Kefir |
| Honey Water | Mead |
| Sweet Tea | Kombucha |
| Sweet (honey) Green Tea | Jun |
| Salsa | Fermented Salsa |
| Pineapple Rinds | Tepache |
| Grapes | Wine |
| Grains | Beer, Bread, Fermented Oats |
| Cucumbers | Pickles |
| Apples | Apple Cider |
| Cream | Cultured Butter |
Although you can make many different types of fermented foods, most of the questions I asked the fermentation experts and enthusiasts pertained to kombucha, kefir, and sauerkraut. So, much of the nitty-gritty details in this post will be centered on those particular foods.
One common theme I noticed throughout my research and the interviews was that people are passionate about fermenting their own foods. Now that I have tried my hand at this, I’m starting to understand why. There is something very satisfying about it. Here are some of the most loved aspects of fermenting foods that were mentioned in the interviews.
Why is fermenting your own food so fun?
1) You can create a customized experience.
“My favorite would be sauerkraut because it has always been one of my favorite foods, and my family hates it. But now that we’re fermenting it, and you can do whatever you want with it, add whatever you want into it, and stop it when you want so you get the taste you want, it’s been really fun,” says John Wertz, PhD, Associate Professor at Calvin College, who has a PhD in microbial ecology, teaches on the subject of fermented foods in his microbiology classes, and also enjoys making fermented foods at home. So, after doing their own at-home fermentations, Dr. Wertz’s family began to like sauerkraut because you can customize the experience. “My wife was like, ‘why don’t we add in dill,’ and she was like, ‘wow this is really good.’”
2) You can learn about different cultures.
In his class, Dr. Wertz explains how different cultures have used fermentation in different ways. “We made injera, a traditional Ethiopian fermented flatbread that is used to eat food, rather than using utensils. Then, we went to an Ethiopian restaurant and talked to them about it.”
3) It’s a unique way to spend time with family.
“My family background on my mom’s side is Ukrainian. And we used to ferment big batches of sauerkraut with my grandfather. And it wasn’t very fancy, we would just take a big five-gallon plastic pail, and you know, shred a lot of cabbage, do the kneading, and leave it out on the porch, weighed down with a plate. And so that was my earliest exposure to fermentation,” says Kristina Campbell, a science writer who specializes in the area of microbiome research, writing on topics such as fermented foods, microbial therapies, probiotics, and microbes in human health. “I think fermenting practices can be a great way to connect with your family and with your cultural roots.”
4) It makes food fizzy.
Campbell shared that she especially likes fermented salsa. “It’s just amazing. You know, after three days, that effervescence comes out, like a real sparkle in your mouth. And I just really love that recipe.”
5) You can experience a variety of foods with unique textures and flavors.
“I’ve made viili, a Finnish yogurt. It’s very thick and stringy. It’s quite strange to look at. It sticks together when you pull it apart. But it’s a really easy fermentation,” says Leech.
“We’ve done fermented oats. That was an interesting one. We’ve done cultured butter. We do sourdough and kefir,” says Madi Myers, AfN Registered Associate Nutritionist and co-owner of the fermented foods company The Crafty Pickle (you’ll hear more about their business in Part 5 of this series).
6) You can replace your soda with a less sugary fizzy fermented beverage.
“I really like the taste of kombucha,” says Leech. But he tells me he’s also made water kefir, which has a less vinegary flavor with all the same fizziness of kombucha. He says it requires more work, though, because you have to tend to it (transfer the water kefir grains) every day.
Another fermented tea beverage similar to kombucha is Jun, which Leech says he enjoys. “I only came across it from collecting samples, but I’m about to begin a project exclusively on kombucha. Jun is honey and green tea as opposed to black tea and sugar — although you can make regular kombucha with black or green tea,” says Leech. “Jun is a bit more subtle than kombucha, so a lot of people like it, but I like the kick of regular kombucha better.”
Myers tells me that she and Serini tried an interesting, fizzy drink made from the flowers of an elder shrub called Socată. “We went and picked a whole bunch of elderflowers and then just fermented them.” She says it tastes sweet and floral, depending on how long you ferment it—if you let it go for a while, it can get very sour and alcoholic.
7) Beer, wine, and more!
Many people enjoy beer and wine, both of which are products of yeast fermentation. But there are other fermented alcoholic beverages that maybe fewer folks have heard of.
One example is mead. “Mead is probably, based on evidence, the oldest fermented food,” says Leech. It is made of honey and water and it can get quite strong, sometimes more than 20% alcohol by volume (ABV).
Another fermented beverage that Leech enjoys is the “pineapple-fermented drink from Mexico tepache, a spontaneous fermentation from pineapple rinds in water with sugar, and let that ferment. But it can explode if you don’t keep an eye on it.” This one is only slightly alcoholic at about 2-3% ABV.
Alright, enough fun. Let’s talk about the risks of fermenting foods at home.
Are there dangers of fermented foods?
There will always be some risks when you ferment foods at home.
But generally, at-home fermentation is safe for a few reasons.
- Many fermented foods are highly acidic, and most pathogens will not survive in this acidic environment. However, if you consume a large amount of acid, it’s not good for you. Moderation is key.
- Many fermented foods — vegetables in particular — are salted to prevent pathogen growth.
- The microbes that produce fermented foods are experts at growing on those foods. These organisms, called the “fermented consortium,” have been producing fermented foods for ages. So they are really good at out-competing pathogens.
“I think there are safety concerns with anything you would do at home. But as long as you do it right, start off right, and have an understanding of the system — what’s going on and what changes that should be occurring — then, it’s pretty safe,” says Dr. Wertz.
Can you get sick from contamination?
In general, getting sick from the contamination of fermented foods is not a concern. Here’s why.
For his PhD project, Leech is characterizing the microbes that are in a range of fermented foods (milk kefir, water kefir, kombucha, sauerkraut, kimchi) from 10 different countries, and he found no pathogens in the fully fermented foods — those that completed fermentation — that he tested.
He says that the microbes that thrive in the fermented foods outcompete the pathogens early on in the fermentation process. Once the pH drops, most pathogens cannot survive.
Leech does hands-on demonstrations for folks interested in fermenting at home, and he tells them, “Most fermentations are generally safe, but I also have to warn people when I do hands-on demonstrations that there is always a risk.”
When it comes to the popular fermented beverage kombucha, if people do get sick, it’s not usually because they were infected with a pathogen. “I’ve looked into the literature on kombucha, and I know there’s been at most two deaths,” says Leech. One death was from lead poisoning because they were fermenting in a ceramic pot (a crock) that likely had a glaze with lead in it. So, what can we learn from this case? It’s best to ferment your kombucha in a glass container. The other death was from lactic acidosis, but this person drank 1 liter of kombucha. And what can we learn from this case? Moderation is key.
This post contains affiliate links — see my disclosure policy.
When it comes to sauerkraut and fermented vegetables, I couldn’t find any evidence of deaths related to consuming these foods. In his book The Art of Fermentation, Sandor Katz says, “it is intrinsically safe.” He adds, “‘as far as I know, there has never been a documented case of foodborne illness from fermented vegetables,’ states Fred Breidt, a microbiologist for the US Department of Agriculture, who specializes in vegetable fermentation.”
Do you need to worry about molds on fermented foods?
Most of the time, you do not want to see mold in your fermented foods. And if you do, you would want to throw them away.
But some fermented foods, Leech tells me, require mold to be produced, like tempeh and cheeses, such as Brie and blue cheese.
The way to prevent mold growth in fermented foods that don’t require them is to keep the environment anaerobic (oxygen-free). When it comes to sauerkraut, you keep the cabbage submerged beneath the liquid. If the sauerkraut is exposed to air, a layer of yeast can grow on the top, which ruins the flavor, Leech tells me.
So, what should we do to ensure safety during our fermentation adventures?
Tips to ensure safe fermentation
1. Be very clean (wash hands, fermentation vessels, and utensils).
In microbiology, we use a method called the aseptic technique, where you think about all sources of contamination and try to prevent those contaminating microbes from getting into whatever you are working with. So, Dr. Wertz says, act as if you were in a microbiology lab — be aware of anything in the kitchen that could be a potential source of contamination. “Bacteria are everywhere.”
“We want to encourage proper food safety and sanitation. So anytime you’re going to deal with any sort of food, you need to wash your hands, first of all, just like you would when you’re preparing food,” says Arthur Serini, who has a master’s degree in nutrition with a focus in microbiology and is the co-owner of The Crafty Pickle along with Myers.
But at the same time, you have to realize that fermented foods are not easily contaminated. Dr. Wertz tells me that a lot of folks think “that it is super easy for them to go bad, be contaminated, or can be dangerous simply because they are not refrigerated and are left out with a cloth draped around the top and a rubber band holding it in place. It seems super backward and super sketchy.”
Hopefully, now you can see that there are relatively few dangers of fermented foods and it will make it easier to try at-home fermentation yourself!
2. Use your senses.
Part of fermenting is a sensory experience. And this is for safety purposes as well as enjoyment. You need to get used to how the fermented foods should look, taste, and smell. “Know what to look out for,” says Myers.
Dr. Wertz gives the following advice: “If you start to notice things going off color, off smell, then probably something has gone wrong, and you shouldn’t eat it or drink it.”
Err on the side of caution. Just throw it away, if you are in doubt.
Here are a few specific tips from Leech to help you decide whether or not to throw your fermented foods out.
Throw out fermented foods if…
- Kombucha tastes too acidic
- Sauerkraut has mold or yeast on the surface
- Milk kefir starts separating into a transparent and solid layer
3. Prevent explosions.
One dangerous aspect of fermentation is the potential for bottle explosions.
These explosions occur when foods are fermented with sealed lids or caps. So, two things you can do to prevent explosions are to 1) burp (open the caps/lids of) the bottles each day and 2) store your sealed fermented foods in a secondary plastic container with a lid.
“We were super lucky, but we had a group that was doing a spontaneous natural fermentation of fruit, using whatever yeasts were on the fruit. And when we came in one morning, all of their bottles were scattered from one end of the room to the other. There was no place in the room that did not have shattered glass. If we would have been in there, it would have been a disaster,” says Dr. Wertz.
4. Salt fermented foods appropriately.
Certain fermented foods require salt for proper fermentation. Salt helps in food preservation and encourages the proper microbes to grow because they are tolerant of the high salt environment.
“We encourage people to use a certain salt concentration that would make sure that we create this environment that’s favorable for them [the microbes],” says Serini.
Measure the salt by weight rather than by tablespoons since salt granules can vary in size, which will change how much salt you end up with based on tablespoons.
“I encourage people to do a little bit of math and use 2% at minimum,” says Serini.
Some parting thoughts
Fermented foods are everywhere, whether you realize it or not. It’s pretty amazing what microbes can do to make our foods not only taste better but also last longer. After reading this, I hope you can walk away knowing a little more about fermented foods and the microbes involved. And hopefully, you feel more at ease and want to try your own at-home fermentation.
If you’d like to learn more, below are some resources to help you dive deeper into the world of fermented foods.
Resources on fermented foods
Keep in mind, when it comes to resources, that it is good to do your own research and do not necessarily trust everything you read online or hear about in a YouTube video, says Dr. Wertz. It’s best to figure out for yourself what the consensus opinion is based on scientific evidence.
And as far as books go, Sandor Katz is well-respected in the world of fermented foods, so check out his books Wild Fermentation and The Art of Fermentation, which were recommended by everyone I interviewed for this post. I do not 100% stand behind everything he says about the health benefits but would overall recommend his books. I have personally read The Art of Fermentation, and I think it is a wonderful and in-depth introduction to the world of fermented foods.
Additional Fermented Foods Resources
- Wild Fermentation – Sandor Katz
- The Art of Fermentation – Sandor Katz
- Chapter 1 The Benefits Of Fermenting Fruits And Vegetables from the book Fermented Fruits And Vegetables, A Global Perspective – Mr. Mike Battcock and Dr. Sue Azam-Ali
- Microbiology and Technology of Fermented Foods – Robert W. Hutkins
Continue Reading the Fermented Foods Series
Thanks so much for reading Part 2 of the Fermented Foods Series. The next post is about the health benefits of fermented foods. Learn whether the health claims around fermented foods are supported by research, get tips on how to identify good resources regarding these health claims, and find more fermented foods resources.
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