lactic acid fermentation
Let's get to know some of our microbe friends.
One of the main methods of fermentation is lactic acid fermentation, also known as lacto-fermentation. This is the primary method of fermenting vegetables, including sauerkraut, kimchi, pickles - as well as yogurt and some cheeses.
Lactic acid fermentation is an anaerobic process (meaning it happens in the absence of air) that occurs in some bacteria and animal cells. Sound familiar? Like when you work out hard and then your muscles are sore the next day - that's lactic acid.
In ferments, the lactic acid bacteria (LAB) consume sugars and produce lactic acid. The lactic acid lowers the pH, creating the signature "sour" taste of fermented foods. This acidification inhibits the growth of spoilage agents and other microbes, making fermented foods some of the safest things on the planet to eat, and easy to preserve.
I've started a series of watercolor microbe portraits to get to know these friendly bacteria better. Lactic acid bacteria are either rod-shaped (bacillus) or spherical (coccus), and characterized by their increased tolerance to acidity.
The order of Lactobacillales includes at its core: Lactobacillus, Leuconostoc, Pediococcus, Lactococcus, and Streptococcus.
The one you hear most about is Lactobacillus. The lactobacillus strain got its name because it was first studied in milk ferments, but it is prevalent in the soil as well, and is involved in fermenting vegetables, not just dairy. Lactobacillus are also present in our own bodies - including as a major player in the vaginal microbiome.
Leuconostoc is great veggie fermenter, including sauerkraut. In addition to lactic acid, Leuconostoc makes diacetyl, which produces a signature "buttery" flavor in fermented milk and meats, and helps with preservation and palatability. It's also really good at inhibiting Listeria.
Pediococcus is also a contributor to the fermentation of sauerkraut and other veggies. Pediococcus are used for making sour beers - like lambic. It also produces diacetyl, which gives a butterscotchy taste to some wines - like Chardonnay. It's commonly added as a beneficial microbe to cheeses and yogurt.
Where do they come from?
Microbes are all around us, and naturally live in the soil (as long as the soil is healthy!). That's why you don't need a starter culture to make fermented vegetables, these microbes are hanging out on the skin of the veggies, and by creating an environment where they thrive - through the use of salt - you can proliferate them and they outcompete other microbes.
The lactic acid bacteria eat the natural sugars present in the veggies, and produce lactic acid. The longer you leave them, the more sugar they eat, the more acid they produce, the more sour it tastes.
The basics of lacto-fermentation (thanks to Amada Feifer of Phickle.com)
Salting the veggies gives lactic acid bacteria an advantage over other microbes that don't like a salty environment, and it also strengthens the pectins in the veggies so they stay crisp. You want to add at least 2% salt to vegetable weight for direct salting, or 4% if you're brining. Too little salt will result in a fast fermentation and mushy veggies. Too much salt slows the fermentation down - and just tastes salty. For a point of reference, seawater is 3.5% salt. You can measure or weigh your salt - weighing is much more accurate, especially because there are many different varieties and grains of salt. Once you get familiar with fermentation, you can also salt to taste - you want the veggies to taste slightly saltier than you would want to eat fresh.
Really the only thing you have to do to care for your ferment once it's started is make sure it stays submerged under the liquid. Any veggies that come in contact with air can mold, so you want to weigh them down and make sure you have enough liquid to keep them under cover. For many veggies, you can create enough liquid just through the salting process to cover them. For others, you'll need to create a saltwater brine.
Lactic acid bacteria prefer temps between 64-78 degrees fahrenheit. The warmer your environment, the faster the fermentation process happens, so if you live somewhere with seasonal changes you'll notice a difference in the amount of time it takes to ferment at different times of the year. Different ferments do better at different temperatures, which you'll learn through experimentation in your unique environment.
Clean, not Sterile:
Unlike canning or home brewing, fermentation does not require sterility - in fact, you want the microbes to survive! You want your equipment and hands to be clean (no funky smells or residues) but you can achieve this through warm soapy water rather than boiling or sanitizing.
Don't use metal:
You want to avoid using reactive metal (anything that's not restaurant-grade stainless steel). The acid in ferments can react metal, creating corrosion, rust, or other chemical reactions.
Don't be shy:
Go ahead and peek.
You're in control here. Taste it: before you ferment, and often during fermentation.
One of the great things about fermentation is getting to know your food better, and learning to trust your senses. You'll know if something is off because it will taste/look/smell off. You'll learn how long you need to ferment based on how you salty, sweet, and sour you like it to taste. Just be sure to tuck everything back under the brine after you're done tasting.
Here's a fun podcast featuring Amanda Feifer talking about fermentation basics.
Lactofermentation is not the only kind of fermentation.
While lactic acid bacteria are the primary fermenters of veggies and some dairy, there are other fermentation processes carried other little critters.
Yeast fermentation: yeasts are the primary fermenters in things like beer and wine.
SCOBY fermentation: you know, that thing they call the "mushroom" in kombucha? It's not really a mushroom, it's a Symbiotic Culture of Bacteria and Yeast (SCOBY). There are lots of fermentation processes that use both yeast and bacteria including:
kefir (milk and water kefir)
Acetic fermentation: acetobacter is a special type of bacteria that require air (most fermentation processes are anaerobic). They eat alcohol and make it into vinegar, which is why you need an airlock if you're making wine or beer, but what they make we also like:
apple cider vinegar
Mold ferments: there are some things that we eat that are actually fermented by mold! Including:
koji - that makes miso, sake, amazake, soy sauce
We'll get into these other fermentation processes in later posts with recipes and other fun stuff.