HOW TO FERMENT FRUIT
Pictured: a fermented fruit appetizer I served at a pop-up: fermented strawberry, shrimp, lemon thyme, oregano, pickled elderflower, and koji oil.
THE THEORY
Intro to lacto-fermentation
Sauerkraut and pickles are made via lacto-fermentation, a natural process where good bacteria (called lactobacillus) break down the sugars in foods to form lactic acid. Lactic acid is sour in a good way — it both preserves foods and and kicks up its flavor.
Since the lactobacillus bacteria can survive in salt and most other bacteria cannot, it’s really easy to lacto-ferment fruits and vegetables. In fact, it’s so easy that you literally just add salt. That’s right, if you weren’t aware, pickles are just salty cucumbers that have fermented their way to their own funky vibe.
Why fermenting fruit is so special
Both cabbage (for sauerkraut) and pickles (for pickles) don’t have that much sugar. As a result, fermented cabbage (for sauerkraut) and fermented pickles (for pickles) just taste sour.
Fruits, meanwhile, are packed with sugar. Once fermented, fruits develop a beautiful acidity that counteract the fruits’ remaining sweetness. Especially once you employ a trick I’ll share later in this recipe, fermented fruits taste like self-contained flavor-bombs. Like healthy fruit loops!
Since their so well-balanced, I add fermented fruits to anything that could use something sweet and sour: salad, ceviche — even as a side with roasted meat.
HOW TO FERMENT FRUITS EFFECTIVELY
Fermenting fruit is technically as simple as adding salt, but you’ve gotta understand the science to do it well. To ferment fruit, you need to:
Add the right amount of salt. You need around 2% of the weight of the fruit in salt. It’s helpful to have a digital scale so you can measure in grams.
Keep the fruit away from air. This prevents bad bacteria from taking over. The easiest way to do this is to use a vacuum sealer.
Ferment at around room temperature. This is for optimal flavor development. Somewhere between 60f to 80f is ideal.
Concentrate the residual sweetness. After the ferment, the fruit will be sweet but certainly not as sweet as a fresh fruit. When you semi-dehydrate the fermented fruit, you concentrate the sweetness back to pre-fermentation levels.
For a detailed recipe (where I’ve chosen strawberries as my fruit of choice), head to the end of this post.
THE GOODS
Vacuum sealer for lacto-fermenting the fruit Fermenting fruits with a vacuum sealer is the most consistent method. Here’s a cheap and reliable one, but see my post on chamber sealers if you want to take your ferments to the next level.
You’ll also need some large vacuum-seal bags. I use these gallon sized ones so there is enough room for the bag to expand during fermentation without the bag popping.
Dehydrator for semi-dehydrating the lacto-fermented apricots. This intensifies the sweetness of the fermented fruit, making it have the best of both fresh and fermented flavors.
Digital scale. You need a scale that measures to the gram, because we’re going to add exactly 2% of the strawberries’ weight in salt. For me, this OXO one has been the most accurate across weight ranges.
THE Recipe
My favorite is strawberries, but try this with any fruit you’d like!
FermentING STRAWBERRIES
Lightly clean the strawberries using a damp paper towel.
Chop the strawberries in half and remove the stems. Skip this step if you’re using small wild strawberries.
Weigh the strawberries with the scale in grams. Pull out your calculator and calculate what 2% of that weight is by multiplying by 0.02. For example, 2% of 600g is 12g.
Weigh out salt equaling the 2% number you just calculated. In the example, I’d weigh out 12g of salt.
Add both the strawberries and the salt to a vacuum seal bag and mix it around. I recommend using a bag that is much bigger than you need (one with room for 2x more strawberries), because the bag is going to puff up with air during the fermentation process!
Vacuum seal the strawberries. You’ll want to make sure that the sides of the bag are totally dry before sealing, because this type of vacuum sealer doesn’t work well with liquids. If the vacuum starts to seep liquid, be quick to press the ‘seal’ button yourself rather than letting it turn on automatically (which might be too late for the seal to form).
Wait! Store the bag at room temperature in a dark place. Over the next few days, the salt will seep juices and air from the strawberries. You’ll start to see the strawberries have more room in the bag until the bag totally puffs up. If you added a ton of strawberries in the same bag, it might look like the bag is about to pop. If you’re worried about this, you can cut open the bag and reseal.
And that’s it! At around day 7, the strawberries will be fermented enough for this recipe. But note! The specific amount of time varies on the temperature and other factors. If your finished product isn’t sour enough for you, feel free to reseal and keep the ferment going.
For the rest of the recipe, we’re only going to use the fermented strawberries. But feel free to save that strawberry liquid for another purpose (e.g. vinaigrette).
DEHYDRATING THE FERMENTED FRUIT
The next step is to dehydrate the fermented strawberries. The dehydration concentrates the flavors, further preserves the strawberries for storage, and adds its own flavors through the maillard reaction.
There are two approaches.
I prefer option 2 because the texture is to die for! It’s like a fruit gusher. Option 2 is also the best for long-term storage (which you can technically do at room temperature).
The downside? Option 2 requires a chamber sealer, which is a special type of vacuum sealer that can vacuum liquids.
Semi-dehydrate them: Dehydrate at 140F for around 8 hours. You’re aiming for a raisin-like consistency where there’s still enough moisture to have a chewy (not dense) eating experience.
Fully dehydrate them and then rehydrate them: Dehydrate at 140F until all moisture is gone (about 16 hours). Then vacuum-seal them with their own fermented juices (saved from the bag).
STORAGE
The fermented fruits will store for many weeks in the fridge in an airtight container. Fermented fruits also freeze very well, especially when vacuum-sealed.