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How to make lacto-fermented fruit, with recipes

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Learning how to make lacto-fermented fruit will give you access to a secret ingredient used by the world’s top restaurants and chefs. In addition to incredible flavor, lacto-fermented fruits also have numerous health benefits. In this article, we’ll show you exactly how you can make lacto-fermented fruit at home. 


For my birthday earlier this summer, The Tyrant got me the perfect gift: The Noma Guide to Fermentation. In case you’ve never heard of it, Noma (a restaurant located in Denmark) consistently competes for consideration as the world’s #1 restaurant. 

One not-so-secret ingredient that Head Chef Rene Redzepi attributes to Noma’s incredible success is fermentation. In fact, fermentation is so essential to Noma’s culinary creations that they started an actual “fermentation lab” that’s equal parts kitchen and science lab. 

The Noma Guide to Fermentation is essentially everything they’ve learned about fermentation over the past decade cooked down into a single book.  

Now, if you follow our website or social media channels, you know that we love fermentation AND eating home-grown fruit.

 

 
 
 
 
 
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Perfect snack. Homemade milk kefir, lacto fermented blueberries from our bushes, and honey from the backyard hive. Gratifying. #gardentotable #fermentation #microbiomehealth

A post shared by Tyrant Farms (@tyrantfarms) on

Thus, the first parts of the book I dove into were all about how Noma makes and uses various lacto-fermented fruits.  

Even though the process of lacto-fermenting fruit is fairly simple and straightforward, I’ve already learned a ton from this book…

What is lacto-fermentation? 

Lacto-fermentation is shorthand for lactic acid fermentation. Species of bacteria in the order Lactobacillales are known as lactic acid bacteria (LAB). LAB species are found on every fruit and vegetable in the world, in the soil, and throughout the human body (primarily in our digestive systems). 

LAB digest carbohydrates and produce lactic acid (which tastes sour to humans) in the process. LAB thrive in salty, acidic, anaerobic (no oxygen) environments — environments which also happen to kill dangerous pathogenic microbes that can make you sick or worse. That’s why human beings have been working with LAB to safely make and preserve food for thousands of years.    

You may not realize it, but your eat and drink countless lacto-fermented products. A few examples:

Lacto-fermented cherries offer an amazing range of flavors that fresh cherries don't have: umami, salty, and tangy with rich hints of the original cherry flavor. Not only do they taste great, they're an amazing probiotic!

Lacto-fermented cherries offer an amazing range of flavors that fresh cherries don’t have: umami, salty, and tangy with rich hints of the original cherry flavor. Not only do they taste great, they’re an amazing probiotic!

Health benefits of lacto-fermentation 

We’ve written in-depth about the health benefits of eating high quality, homemade fermented foods in our article Fermentation: how to tend your microbial garden for better health.

The short of it: human beings have more microbial cells in their body than human cells. Our microbial partners keep us alive, healthy, and working well — both physically and mentally. They also fend off pathogens, helping to keep you from getting sick.  

Without our symbiont microbial partners, we humans don’t work well. One great way to inoculate yourself with lots of beneficial LAB microbes is to make and eat lacto-fermented fruit, ideally from your own foraged or homegrown organic fruit. 

How to make lacto-fermented fruit 

1. The basic ingredients of lacto-fermented fruit

Making lacto-fermented fruit is quite easy. The only ingredients you need for basic recipes are:

Ingredients for lacto-fermented fruit can be as simple as two ingredients: fruit and salt. Pictured: Himalayan pink sea salt.

Lacto-fermented fruit can be as simple as two ingredients: fruit and salt. Pictured: Himalayan pink sea salt.

Getting the ratio of salt-to-fruit correct is essential for preventing contamination since you want to promote the proliferation of LAB which thrive in a slightly saline, acidic environment where pathogenic microbes can’t live. According to NOMA’s tests, the ideal salt-to-fruit ratio for best flavor, texture, and safety is 2% salt to total weight of fruit.

For instance, if you have 20 ounces of blueberries you want to lacto-ferment, you’ll need to add 0.4 ounces (~11 grams) of salt. We should also add here that you really should have a good kitchen scale if you want to make lacto-fermented fruit (or make good baked recipes, for that matter) to make sure your measurements are precise. 

If you start branching out and adding more ingredients to your lacto-fermented fruit, you’ll need to account for the weight of those additional ingredients before measuring and adding your salt. For instance, if you add herbs and honey to the fruit, weigh them all together, then calculate 2% of the total weight to determine how much salt you need. 

Herbs can infuse your lacto-ferments with incredible flavor. In the recipe below, we use this 'Opalescent' purple basil with peaches.

Herbs can infuse your lacto-ferments with incredible flavor. In the recipe below, we use this ‘Opalescent’ purple basil with peaches.

Make sure you mix all ingredients together in a bowl and scrape all the salt out of the bowl when putting it into your fermentation vessel. 

2. Lacto-fermented fruit containers/vessels 

You don’t have to have any fancy equipment to make lacto-fermented fruit. For this article, we used the following:

  • glass canning jars we already had,
  • glass lids with glass shot glasses as weights to hold the fruit down and submerge it as the water extracts from the fruit,
  • saran wrap with rubber band to prevent fruit flies or other microbes from coming in (*you may have to “burp” your ferments to let trapped CO2 out). 

NOMA uses ziplock bags for their ferments. Perhaps we’re overly cautious, but we don’t like the idea of housing acidic, biologically active foods/liquids inside plastic containers for days at a time. We can’t find any studies that measure the potential leaching of plastic compounds into fermented foods made in plastic containers, but we take the precautionary principle approach in our own kitchen. 

Our recommendation when making fermented foods: use either glass, lead-free ceramic crocks, or silicone containers. In fact, we intend to get silicone food storage bags to help take our lacto-fermented fruit game to the next level.  

The nice thing about silicone food storage bags is you can remove all the oxygen from your fermentation immediately at the start. When using jars or crocks, you have to wait for the salt to pull enough water from the fruit to submerge it before the fermentation goes anaerobic. 

Kham yeast forming on the top of a batch of lacto-fermented peach and purple basil. Nope, kahm yeast isn't dangerous, it's just unsightly. Skim it off or scoop it out of your ferment. Kahm yeast is more likely to form when you're lacto-fermenting in jars with air inside, as seen here, vs silicone bags.

Kham yeast forming on the top of a batch of lacto-fermented peach and purple basil. Nope, kahm yeast isn’t dangerous, it’s just unsightly. Skim it off or scoop it out of your ferment. Kahm yeast is more likely to form when you’re lacto-fermenting in jars with air inside, as seen here, versus silicone bags.

While kahm yeast (pictured above) is not something to worry about, you never want to eat ferments that have mold growing on them (very unlikely unless your ratios or process were off) or ferments that smell foul.   

3. Temperature, time, light

Temperature

The ideal temperature range for fruit lacto-fermentation is between 70-82°F (21-28°C). A ferment will take a little longer to develop at the bottom end of that temperature range; on the warmer end, it will take less time. 

Time

How long does it take to lacto-ferment fruit? Usually about 7-10 days, but the exact answer can only be known by daily tastings, e.g. let your mouth inform your decision. Chopped fruit goes faster, usually a little under one week; whole skin-on fruit usually takes over a week. 

If not lacto-fermented long enough, your fruit isn’t very interesting — it basically tastes the same as when you started just with some extra saltiness. Fermented too long, and the fruit is too sharp/sour with few of the original fruit notes left.

As NOMA says, “An ideal lacto-fermentation should maintain the essence of the original raw product, but with added acidity, umami, and depth of flavor.”  

Lacto-fermented blueberries from start to finish. Blueberry juice in the jar on the right extracted more quickly than the jar on the left. Our guess is that a little more salt ended up in this jar at the start. Note how at Day 10 (completion) the blueberries are lightly bubbling as the LAB off-gas CO2 as they digest the sugars in the blueberries. We knew this batch was done based on a taste test, a subjective decision.

Lacto-fermented blueberries, from start to finish. Blueberry juice in the jar on the right extracted more quickly than the jar on the left. Our guess is that a little more salt ended up in this jar at the start. Note how at Day 10 (completion) the blueberries are lightly bubbling as the LAB off-gas CO2 as they digest the sugars in the blueberries. We knew this batch was done based on a taste test, a subjective decision.

Light 

Don’t place your lacto-fermenting fruit containers in sunlight/sunny windows. Place them in a spot where you won’t forget about them, but that doesn’t get direct sunlight. For us, that’s the ledge above our kitchen sink.  

4. Types of fruit to lacto-ferment – and how to use them

Lacto-fermenting a fruit completely transforms its flavor in indescribable yet delightful ways. And each type of fruit is different… 

Homegrown organic peaches, blueberries, and blackberries... If you can grow it, you can lacto-ferment it.

Homegrown organic peaches, blueberries, and blackberries on their way to lacto-fermentation.

According to NOMA: 

“As LAB ferment sugar, the resultant lactic acid mingles with the acids already present in the fruit. Citric acid — most commonly associated with citrus fruits but also found in many other fruits and berries — can be quite tart and almost give off a burning sensation. Malic acid, found in grapes and apples (think of the tartness of a Granny Smith), is much rounder and mouthwatering. Ascorbic acid is sharp and direct, and can be found in all kinds of tropical fruits, from bananas to guava. The interplay of different acids is one of the most interesting and beautiful facets of fermented fruits.” 

With larger fruits like plums and peaches, you’ll want to cut the fruit into smaller, bite-sized chunks and remove the pits/seeds prior to fermenting. Smaller fruit with no pits (like blueberries, raspberries, and blackberries) can be left whole to lacto-ferment. 

Whole blackberries and chopped peaches starting to lacto-ferment.

Whole blackberries and chopped peaches starting to lacto-ferment.

You’ll also notice that the salt is able to draw the water out of cut fruit far faster than whole fruit with skin on. For example, our cut peaches and cherries are completely submerged in their own juices within ~12 hours, whereas it will take several days before whole blackberries or blueberries are submerged. 

5. Using lacto-fermented fruit

How do you use lacto-fermented fruit? Let your imagination run wild! 

You can pull the whole fruit out of the brine and use it on top of yogurt of milk kefir with a drizzle of honey or maple syrup. You can blend it all together and use it as meat rubs or to baste on corn on the cob — another NOMA idea, which is amazing. (See our article How to make cast iron corn on the cob with lacto-fermented fruit rub.)

There are few dishes you make that won’t be improved visually or flavor wise by the addition of your lacto-fermented fruit.  

Finished lacto-fermented blueberries. We strained this batch to use the lacto blueberries on top of milk kefir. The strained blueberry brine can be used as a salty, flavor-rich base for other recipes or drizzled on top of a salad..

Finished lacto-fermented blueberries. We strained this batch to use the lacto blueberries on top of milk kefir. The strained blueberry brine can be used as a salty, flavor-rich base for other recipes or drizzled on top of a salad..

Note: We don’t mind the small seeds of blackberries or blueberries, but if you do, strain them after blending when making lacto-fermented rubs/sauces with them. 

Recipe: Lacto-fermented peach, honey, and purple basil 

Lacto-fermented peaches, purple basil, and honey - so delicious!

Lacto-fermented peaches, purple basil, and honey – so delicious!

Once you get the hang of the basics, you can start adding new and interesting ingredients to your lacto-fermented fruit experiments. This year, we had a bumper crop of organic peaches, giving us ample fruit for experimentation. 

We also just harvested over 50 pounds of honey from our hive. Lastly, we’re growing a gorgeous ruffled purple basil named ‘Opalescent’ from our favorite organic plant breeder, Frank Morton, at Wild Garden Seed

Morton describes ‘Opalescent’ thusly: “the fragrance and taste are completely distinct from sweet basil, and the fruity sweetness and cherry-magenta color it imparts to a salad vinegar is unlike any other herb I know. Beautiful beyond belief in a bottle with olive oil.”   

Hmm. 

What happens when you lacto-ferment tree-ripened organic peaches, honey, and Opalescent purple basil together? An exquisite flavor combination that defies description.

'Opalescent' basil, peaches, and honey made a wonderful lacto-fermented flavor combination. Fun fact: Shun knives make every kitchen picture look better!

‘Opalescent’ basil, peaches, and honey make a wonderful lacto-fermented flavor combination. Fun fact: a Shun knife makes every kitchen picture look better!

All we can say is we hope you’ll make this recipe and enjoy it as much as we do, eaten as-is or blended into rubs to bring incredible flavors to other dishes. 

Print

Lacto-fermented peaches with honey and purple basil

Course: Side Dish
Keyword: lacto-fermentation, lacto-fermented fruit, lacto-fermented peaches

Some of the best flavors of summer combined into one delicious, easy-to-make lacto-fermented recipe. Wonderful strained and eaten as a chilled savory side salad, on top of fish, or blended into a rub for corn on the cob and other dishes.

Ingredients

  • 2 cups chopped peaches (about 13 ounces) chopped 3 peaches
  • 1 cup loose packed purple basil
  • 1/2 tablespoon pink Himalayan sea salt (exact qty: 4.2 grams)
  • 1 tablespoon honey

Instructions

  1. Chop peaches into bite-sized chunks. Remove basil leaves from stems. Weigh peaches, basil, and honey then calculate 2% of total weight to determine exact amount of salt needed. Stir in salt.

  2. Add mixture to fermentation vessel (see options in article). Start sampling daily around Day 4 to determine when ideal flavor achieved, ours took 6 days at a temperature between 70-72 degrees F.

  3. Refrigerate to slow fermentation, or freeze to stop fermentation. Ingredients can be strained from brine and served as topping or chilled side salad. Or all ingredients (including brine) can be blended together to make rubs or sauces.

Let us know what fruit you lacto-ferment in your kitchen and how you use it! 

KIGI,

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2 Comments

  • Reply
    Aaron Ross Palmieri
    July 31, 2020 at 4:28 pm

    I was curious what you do once the lacto-fermentation has hit the peak (like when you hit day 10). Do you just freeze it or put the fruit in a new jar without the brine?

    • Reply
      Aaron von Frank
      August 2, 2020 at 9:05 am

      There are two parts to the answer: 1) how do you arrest fermentation, and 2) what do you (or can you) do with the lacto-fermented fruit + brine?

      1. When your fermentation is done, you’ll need to slow or stop the microbial activity. Putting it in the fridge slows the LAB’s metabolism to a crawl and you can probably leave it in the fridge for 6-8 weeks without too much flavor change. If you freeze it, obviously this completely stops microbial activity. The option you choose here is going to come down to how much end product you have, how quickly you can eat it, or what you intend to do with it.

      2. As far as WHAT you do with lacto-fermented fruit/brine, there’s no single right answer and it can even vary by fruit. For instance, we like to strain our blueberries out of their brine and use the lacto blueberries as a topping on fermented dairy products like kefir (with a little honey). The brine is great added to sauces, salad dressings, etc. But you don’t have to separate the brine from the fruit. You can just put the whole ferment in your fridge as-is and use it slowly over the next month or so, or you can blend it all together. For instance, with the peach-basil-honey lacto-fermentation recipe in this article, we blended all the ingredients together at the end and have been using it as a rub on finished corn on the cob. But we could have also strained the peaches + basil and used them for other applications.

      Short answer: there is no single answer and you can experiment with each lacto-fermented fruit recipe you make to establish favorite use methods and discover new ones.

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