This past weekend, I had the opportunity to teach my favorite class, Intro to Lacto Fermentation. The energy in the room is always palpable, brought to the table by the open minds of beginners. So often, especially as adults, we resign to narrow perspectives, believing we already fully understand a familiar topic. I returned to one of Meredith's blog posts, which breaks down the multi-layered processes of fermentation, and you know what? I learned a thing or two. Hope you enjoy it.
How to Ferment Food by Meredith Leigh
Fermenting food has been a thing for almost as long as people have been eating but the science of how to ferment food is only more recently understood. What are some of the processes happening in food as it moves from fresh to preserved? As culinary fermentation experiences a renaissance in modern kitchens, the question of how to ferment food is an excellent one, because there is not just ONE way. Fermentation has been described as “controlled rot” and while that sounds dramatically enticing that’s really only sort of true, in some fermentation situations. Fermentation is actually the prevention of rot, via a stewardship of microorganisms. So while bacteria, yeasts, mold and enzymes are indeed responsible for rot, the type of microbe and the resources it is given and the interactions it experiences can change the result. Wait. So, microbes create spoilage, but they also create shelf stability? Does that sound confusing? Let’s take a closer look at how to ferment food, and it will all make more sense.
How to Ferment Food: Salt
Key to understanding of nearly all the pathways of fermentation is salt. Salt is not just a flavoring agent in the kitchen is a superhero of chemical and biological reactions. Every living thing contains salt, and so using salt to control reactions that you want to produce in living foods allows you to affect moisture, processing time, and type of reaction. Salt does lots of things in fermentation, and you’ll learn different benefits of salt as you explore different types of food preservation. What is important to know at the outset is that salt stabilizes a lot of fermentation processes by excluding the microbes we don’t want, therefore buying us time as the microbes we do want go to work. The other thing about salt is that it alters moisture in foods depending on how it is used. It can encourage moisture to come out of the cells of food items, or it can make moisture want to stay inside the cells of food items. What you are trying to do, and often the climate where you are trying to do it, will ultimately decide what level of salt is optimum.
How to Ferment Food: Bacteria
One of the most accessible ways to get into food fermentation is through lactofermentation. This is the stewardship of bacteria in the group lactobacillus, as well as some of their friends, in order to consume the sugars in foods and metabolize those sugars into lactic acids. This is the process embodied in the creation of products like sauerkraut and kimchi, brine fermented pickles, and yogurt, to name a few examples. While species of lactobacillus (and their friends, like pediococcus species) are also responsible for food spoilage, the key difference in fermentation is the addition of salt. Salt at specific quantities will stabilize the environment and also draw moisture from the food. In the absence of salt as an ingredient, that same food might rot from similar bacterial players. While this might make beginner fermenters nervous, the parameters are pretty well established for quantities of salt, temperature, and time that can allow you to dip your toes into the microsphere without worrying too much. Our course Mastering Fermented Vegetables is a perfect segue into bacterial fermentation processes that will yield tons of terrific, delicious results. In our free webinar Fermenting Oats, you will learn how to use lactofermentation to make oats more digestible and delicious. For a lighter foray, check out How to Ferment Sauerkraut and Pickles.
How to Ferment Food: Yeast
Another pathway to food preservation is yeast fermentation. Yeast fermentation occurs in products like sourdough bread, beer, wine, and cider. And it’s important to remember that none of these pathways are super discreet. So, when we say “bacteria” fermentation we mean that the process is dominated by bacteria, but there will be yeasts and other types of microbes involved. When we say a fermentation process is a “yeast” fermentation, it just means that the yeasts are the dominant group. But one of the key things to understand when asking how to ferment food is that microorganisms do not ever ever ever exist in isolation in the natural world. They live in consortia, or in community, just like you and me, especially when we are at our best. Anyway, yeast fermentation happens when yeasts dominate in the microbial community that is present in the food prep. This is usually due to the type of sugar that is present. Yeasts like different sugars from bacteria (mostly) and they also metabolize sugar differently (tomato, tom-ah-to) and so the result is therefore different in flavor, form, etc. But the result is also same, as in: food is preserved. Yeasts produce alcohols from their consumption of sugar (to-mah-to, or rather….wine, beer, cider) while bacteria tends to produce acids (tomato…er…sort of). This is all WAY over generalized, but these are the BASICS, ok? Yeast fermentations are also some of the lowest salt fermentations, with some requiring no salt at all. If you’re interested in yeast-dominated fermentation, check out our course Flower Power: Capturing Wild Yeasts for Fermentation.
How to Ferment Food: Acetobacter
Now we are going to really bend the generalizations, because we’re going to introduce you to a totally different group of bacteria, generally known as “acetobacter.” These friends eat alcohol and poop out acetic acid, which is otherwise known as vinegar. And so you can guess where we use our relationship with these microbial allies. The reason I mention this group now instead of earlier in the bacterial fermentation space is because you have to have alcohol before you can invite acetobacter to the party. And as you just learned, you gotta have yeast to get alcohol. Savvy? This is why we often answer the question of how to ferment food with many answers, because there are many pathways, many layers, many roads to get to Oz. Another thing to know about acetobacter which helps you understand how to ferment food, is that acetobacter needs oxygen in order to do its work. This is totally different from our earlier bacterial friends like lactobacillus. Lactobacillus in a fermentation situation wants no oxygen. This is another thing that keeps the food stable while fermentation is happening. Pretty cool, right? If you’re interested in acetic acid fermentation, check out our course on How to Make Vinegar. And there is a little bit about consortia of microbes that include acetobacter in our course How Fermentation and Curing Works. This course covers ALL the pathways mentioned in this article, and a little bit on kombucha which is a mind-bending little make that straddles bacteria, yeast, and acetobacter to produce a thing we all love that isn’t quite vinegar…or wine… or cider. Wow. Yeah. (How to ferment food was a bigger question than you thought.) Kombucha Fundamentals will take you through how yeast and acetobacter become a delicious beverage.
How to Ferment Food: Fungus
Fungus on food? Yes, of course. Haven’t you ever had a bloomy cheese or a salami with that delicious white stuff on the outside of it? Ever had miso? Sake? Soy sauce? Coffee? Indeed, all of these foods would not taste the way they taste without the fabulous world of fungus, and namely a specific little family of fungi you might know as MOLD. Molds are special because they protect food from other microbes as they grow on the food surface, and while they are doing that they produce enzymes. Enzymes are proteins that zoom biological reactions into warp speed, like little jet packs. So for example, if something might happen anyway, the enzyme makes it happen faster. Or in some cases, something might not happen at all without a little kick in the pants from an enzyme or two. So, in fermentation, enzymes become extremely important because they can speed up favorable reactions, like the breakdown of a big complex sugar into a small one so it can be food for other microbes, (or the breakdown of the actual structure of food itself, see autolysis, below.) The other thing about molds is that they have their own flavors and characteristics, and so foods preserved with molds often take on a signature flavor of the friendly molds that humans have come to appreciate. (Thanks, fuzz-that-I-used-to-fear!) If you’re following all the pathways as you read, you can probably see how fungal fermentation adds layers to the process of fermentation, right? If fungus produces enzymes that unlock molecules, then those molecules like sugars will be available to yeasts and bacteria. And then those pathways will be happening in the same food to produce flavors we all love while achieving preservation.
If you are interested in how to ferment food with fungus, check out How Fermentation and Curing Works, Koji Charcuterie, How to Make Tempeh, or one or both of our miso classes, or How to Make Fermented Sausages.
How to Ferment Food: Autolysis
Autolysis isn’t a microbe, it’s a process, but it is worth mentioning here because it goes along with the pathways of fermentation in many different preserved foods. Truthfully, autolysis refers to the process of an organism being broken down and deconstructed. And yes, while this might seem like the same thing as decomposition, the difference is that autolysis usually refers to breakdown of an organism using the enzymes that are already in the organism, whereas decomposition is the breakdown of matter due to the action of outside microbes and enzymes. Ahem. So, in short all organisms have enzymes inside of them that will only wake up when that organism dies, and these enzymes will go to work sort of eating their own house. Ahem. This process is actually really, really useful in how to ferment foods, because it allows for things like salami and fish sauce and even some misos to have the amazing complex flavors that they have. I mention autolysis because it is important to understand that the flavors and successful stability of fermented foods comes from ALL of these things: salt, and added flavors like spices and stuff, and all these microbes, and the things microbes do while they are alive (pooping out acids or alcohols, for example), and the things that organisms produce when they die (like enzymes for autolysis), and the interactions between all these things all at once.
If you are interested in fermentation products that rely on autolysis, check out How to Make Garum, How Fermentation and Curing Works, or How to Make Charcuterie.
It’s amazing isn’t it? How to ferment food is a science we both understand and don’t, because it is a super dynamic synergistic thing. We may understand the players and their roles, but the things they do together are some of the most fantastic and bombastic things on the planet. And to ferment safely and confidently we don’t have to track every outcome or every reaction. All we really need to know are the parameters and possibilities, and then the world opens into some really amazing realms for creativity and deliciousness. At the end of the day, that’s what makes fermentation ultimately fun for me— that nature does it for me. Meanwhile, the journey I get to go on, and the results that are different nearly every time ensure that my life is full of flavor and wonder.
You made this piece more than just an interesting read. It's been a fun read. Thank you.