Chances are, you’ve heard about fermented foods more than once in the past few years, as this awesome traditional method of food preservation is undergoing a massive reboot and becoming part of everyday language.
These days, you can go into pretty much any supermarket or grocer and find something fermented: you may be familiar with things like kombucha, kefir, kimchi and sauerkraut, but did you know that many mainstream foods are the result of fermentation as well? Bread, cheese, yoghurt, sour cream, beer, wine, apple cider vinegar, soy sauce, Worcestershire sauce… You’ve probably been eating fermented foods without knowing for years!
You’ll see some fermented foods on the shelves, and the good stuff will be in the fridges. This is because active fermented foods are full of living beneficial bacteria, which is why they’re good for your gut health. Left at room temperature, these bacteria will continue fermenting, thus changing flavour: so they’re kept chilled because this slows fermentation right down.
This article is designed to give you a run-down on what fermentation is, how it works, and how to have a go at doing it yourself. You can find some simple recipes to try here, and if you’re interested in learning more, we’ve got a list of awesome fermenty people to check out down the bottom.
Don’t be discouraged by the wordiness of this post – we’ve tried to keep things ‘chatty’, and to pre-empt the questions you might have about the process. Before we discovered Sandor Katz’s brilliant book Wild Fermentation, we found that most recipes were really clinical and left us feeling unsure about lots of things, so we’ve gone for the opposite effect. 🙂
Fermenting: what is it?
Fermentation is a natural, controlled anaerobic (oxygen-free) process that food undergoes which converts carbohydrates into acids or alcohol and gas. There are a couple of different types of fermentation: regular fermentation uses yeasts to turn the sugars in grains, fruits and vegetables into alcohol; Lacto-fermentation uses bacteria to turn the sugars in grains, fruits and vegetables into lactic acid.
Put simply, food is kept away from oxygen, harmful bacteria are kept at bay, and good bacteria thrive whilst turning the food-sugars into acid/alcohol which stops the food from decomposing.
What’s all the fuss about?
Fermenting is arguably THE easiest form of fresh food preservation, it has multiple documented health benefits, and it’s almost impossible to stuff it up. That’s why it’s been done in so many cultures for so many centuries, and is probably why it’s becoming so popular again. It has been proven to boost immunity; improve gut health; makes foods easier to digest which means you get more nutrients from every bite; and there’s evidence to suggest it has benefits for mental health, heart health and even weight loss.
And then there’s the flavour! Fermenting food allows all sorts of nuanced flavours develop, mixing sweet, salty, savoury and umami together in varied and wonderful ways. Generally speaking, the longer you leave something fermenting, the bolder and richer the flavours, so you can experiment with different recipes, and then delve even further by letting things ferment for different lengths of time before eating. Remember that fermented foods are preserved, so you can really play around with times: many traditional recipes call for ageing times of 12+ months for really complex flavours.
Lacto-fermentation is the process used to make yoghurt, kimchi, pickles, sauces, salsas and sauerkraut along with a whole lot of other delicious goodies, and it’s what we’ve been focusing our learning on for the past few years. Lactobacillus bacteria are found naturally on the surface of most fruits & veggies, and when they’re allowed to thrive in an anaerobic (oxygen-free) environment, they quickly convert sugars to lactic acid, which then preserves the food. Lactobacillus are like the superhero of the bacteria world – where others wither and die a rapid death in the presence of salt, they multiply, don their capes, and begin transforming regular food into invincible morsels of supercharged nutritious deliciousness.
There are lots of bacteria that want to get a meal off your jar of shredded fruit and veg, so it’s important to make sure Lactobacillus has the upper hand when you’re fermenting, and the easiest way to do this is to shove the whole lot under salty water. Most bacteria and yeasts can’t survive in a saline environment, so surrounding your fresh fruit & veg with brine (generally speaking, a 2-3% salinity level is sufficient) knocks all the would-be contenders out of the race, and allows Lactobacillus to forge ahead and populate their surroundings.
Don’t let the science behind it frighten you off: remember that nannas and grandpas have been preserving food in the most rustic of settings with the most basic of equipment for centuries. There’s something massively satisfying about being able to transform simple veggies into a fridge-full of colourful condiments with nothing more than a bit of salt and some time, so let’s get you started!
How to lacto-ferment food
Sandor Katz – known around the world as The Godfather of Modern Fermenting – has described fermenting food as simply “Chopping s*it up, adding salt, and leaving it alone”. This is a really great mentality to hold onto when fermenting, as it helps demystify the process and allows you to feel confident in just having a go.
There are lots of variables when it comes to each individual ferment – vegetable type, size and density; fermenting vessel size; supply requirements; what flavours you’re chasing; fermenting location; seasonal/weather conditions – so it’s good to have an understanding of the basic principles rather than constantly relying on different recipes. This will allow you to adapt your skills so that you can confidently make fermented foods in any situation.
We’ll give you a more specifics further down, but keep in your head that the general rule is:
Use what you have, and make it so you like the taste.
As mentioned earlier, it’s almost impossible to truly stuff up a basic ferment, but there are occasional hiccups – mould, soggy veg, surface yeasts – that can arise. We’ve seen them all along the way, but problems like these are nearly never a reason to despair. There are fixes for most potential issues, so even if you’re not confident, have a go and only worry about solving a problem if and when it arises. The beauty of starting your journey towards Being A Fermenter with something simple like sauerkraut is that it’s incredibly cheap to make, so even if things do go irretrievably wrong, you’ve only lost a couple of bucks and a bit of time.
Step 1: Find your vessel
Because lacto-fermenting involves brine, it’s important not to use vessels or tools that are going to rust or degrade when exposed to salt. Suitable vessels will be made from glass, ceramic, stone or plastic (all food-safe, of course). You can also use enameled vessels, but the enamel must be completely free from cracks or chips or the salt will seep through to the metal underneath and cause issues.
You can sterilise your glass or ceramic vessels before use by either heating in a 100C oven for 10-15 minutes, but to be honest, it’s usually not necessary. Just a thorough wash & rinse with hot soapy water is enough: the salt will to kill off the bad bacteria in the vessel anyway.
You can purchase special fermenting crocks which help keep oxygen out of your fermenting environment, but remember that people have been using simple tools to ferment for centuries. We just use large glass, ceramic and food-grade plastic jars.
Step 2: Work out what you’re fermenting
The main aim in lacto-fermenting is to surround your plant material with a 2-3% (or higher) brine. this means for every 100ml of liquid in the vessel, there should be 2-3g of salt.
When you’re using softer fruits and veggies like tomatoes, cucumbers, plums etc, there’s already a high level of water in them, so you can just add the salt, but for firmer, crunchy veg like carrots or chillies, there’s not enough water present in them to produce a brine, so you make a separate brine to submerge the plant matter in.
Work out whether you’re making crunchy ferments where you’ll need to mix up a brine first (like dilly beans or cheat’s pickled onions), or a soft ferment (like salsa, sauerkraut or kimchi) which will just need salt.
Step 2.1: Mix some brine (if needed)
Use pure salt with no preservatives in it. Preservatives can negatively affect both the flavor, texture and appearance of ferments. Use lake, sea, rock, river, ‘pickling’ or kosher salt.
Make sure your salt is finely ground so it distributes evenly. This also affects your measurements (rock, flake and ground salt fill a tablespoon differently, so you might not get enough salt if you use 1tbsp of rock etc).
Either use filtered, spring or rain water, boil it, and then add 1tbsp pure salt to 500ml water and allow it to cool. NEVER pour hot brine over your veggies, as it will kill the bacteria you want working for you.
This website has an excellent calculating tool for working out how to get exact salinity/brine concentrations, so if you’re after a bit of guidance, take a look.
NOTE: Increasing the salinity (salt concentration) of your ferment will cause it to ferment more slowly, and vice versa. You may like to add more salt during warmer months (which will hinder undesirable bacteria & yeasts from kicking off in the heat), and less in winter. Never dip below 2-3%, or else harmful bacteria may survive. 5% is considered pretty darn salty, and 10% is about as high as we’d ever go. With things fermented in higher-level brines, we’ll often rinse them before eating, otherwise they’re not that pleasant to eat.
Step 3: Chop/prepare your fruit or veg
Size is totally up to you, so don’t get caught up in super specific measurements in recipes.
Simply: the bigger the pieces, the longer it will take to ferment. If you want a quick ferment, chop things up smaller. This increases the surface area of the pieces, which in turn allows the salt to draw out liquid, and the Lactobacillus to work their way through the pieces more quickly.
Step 4: Combine your fruit or veg and salt
If you’re going for firm, crunchy pieces of fruit or veg surrounded by premixed brine, shove the fruit/veg into the vessel quite tightly, then pour the brine over them until they’re well covered.
If you’re after a softer, more juicy ferment where you’re adding salt and getting the liquids from inside the fruit or veg (eg salsa or sauerkraut), combine the fruit/veg in a bowl and weigh how much you have. Work out what 2-3% of that weight is by multiplying it by 0.02-0.03. That’s how many grams of salt to add. (eg 500g chopped tomatoes, capsicum, onions, garlic & corn needs 500 x 0.03 = 15g of salt)
Combine that salt with the fruit/veg, mix well, and then stuff into the vessel.
NOTE: With softer ferments, it may not seem like there’s enough brine to submerge the veggies at first, but under a weight overnight, the pressure should help more liquid leave the veggies and create plenty. If it’s still not enough though? Just mix up some brine and top it up with that.
Step 5: Keep your fruit or veg submerged
Lacto-fermentation is an anaerobic process, so you need to keep the air away from your bits and pieces by keeping them submerged under the brine. Fancy fermenting vessels have glass or ceramic weights you can use, but there are lots of other options.
A clean glass jar filled with water that fits inside the neck of the vessel. An outer cabbage leaf or two folded over and shoved into the vessel so it sits snug against the sides. A food-grade plastic ziplock bag filled with brine (in case it splits – plain water would affect the salinity of your ferment & could cause it to spoil) stuffed into the vessel. A small clean plate with a boiled-clean river rock on it. Half an apple that’s the width of the vessel with the flat side facing down. We’ve used all of these with success.
Another option is even more freehand than these: you can simply stir the ingredients with a clean utensil, or seal the vessel and shake it vigorously a couple of times a day, so that the bits at the surface (that are exposed to air, which can enable moulds & yeasts to grow) are switched around with bits that have been submerged. This method works fine too, and is usually how we make our chilli hotsauce.
NOTE: If you use a folded cabbage leaf, it doesn’t matter if it pokes above the brine and grows mouldy. You’ll compost it anyway, and everything under the brine will be perfectly fine.
Step 6: Leave it alone
Lactobacillus operates best in temperatures between 13-29 degrees Celsius (55-85 degrees farenheit), so you want to find a spot in your house that’s going to stay somewhere within that range. The cooler it is, the slower the ferment will be (and the longer it will take to be ‘ready’) and vice versa. Longer, cooler ferments allow more nuanced flavours to develop, but also open up the door to softening of the plant tissues (which means soggy ferments). Quicker, warmer ferments are ready sooner, but there’s a greater chance that undesireable bacterial or yeast colonies could thrive and take over.
Ideally, you want a spot somewhere out of direct sunlight where the temperature will stay around 18-22 degrees Celsius. A kitchen or laundry bench away from windows and electrical heat sources is great. When in this temperature range, it should take 3-5 days for lacto-fermentation to begin.
NOTE: It’s a good idea to cover your vessel with something to prevent dust and bugs from entering, but allow the gasses created during fermentation to escape. This could be as simple as covering it with a clean teatowel or plate, or you could keep the vessel sealed and ‘burp’ it by opening the lid a couple of times a day to release the gasses. You can also remove the rubber seal in traditional glass clip-top jars before closing them: the tiny gap between jar and lid is enough for gasses to force their way out. If you have a fermenting vessel with an airlock in the lid, none of these will be necessary.
Step 7: Observe and interact
After 3-5 days, you should notice some bubbles rising to the brine surface. This is a sign of active fermentation. Sometimes the gasses/bubbles try to lift the veg/fruit pieces above the surface: if that happens, just push them down with a clean utensil and top up with more cool brine if required to keep them submerged.
When the brine goes cloudy and there are lots of bubbles, it’s a sign that your fruit/veg is coming along nicely. At this stage, you can begin tasting your ferment. A fermented fruit/veg will taste nicely sour, and have some complex flavours going on. If it still tastes sweet, you may like to leave it fermenting for a bit longer. Once you’re happy with the taste of your ferment, seal the jar with an airtight lid, and place in the fridge until you’ve eaten it all. Most ferments will last 3+ months in the fridge with little change to their texture, and many can last well over a year.
NOTE: Older ferments can develop a bit of a fizzy texture/taste: there’s nothing wrong with them, and they’re safe to eat, but you may prefer to cook with those instead of eating them raw if the feeling on your tongue is off-putting.
It’s also worth noting that ferments made with cabbage or other cruciferous vegetables (kale, broccoli, cauliflower, radish, daikon etc) will let you know they’re close to ‘ready’ when they start giving off a …. how to put this?… particularly farty smell. When you walk in the front door, and your kimchi welcomes you with a smack in the face of ‘ripe’ odours, it’s probably time to seal that baby up and tell it to cool its jets in the fridge. 😀
So! That’s our basic rundown of lacto-fermenting fruits & vegetables. Hopefully it has left you feeling encouraged to have a go and see what happens. There are some simple recipes for you to try below if you like. And if you’re interested in learning more from fermenting experts, we heartily recommend taking a look at Sandor Katz, Pascal Baudar, Sharon Flynn and Mandy Hall.
Here are some simple fermenting recipes to get you started