How to Do a Kefir Second Fermentation {+ Flavoring Kefir}

Making milk kefir is not only fun, but it's also very inexpensive and easy to do! One of my favorite things about making my own kefir is how easy it is to add flavors WITHOUT all the additional sugar that is common in store bought versions.

Doing a milk kefir second fermentation is the key to adding both flavor and bubbles (AKA effervescence), and it also gives a great probiotic boost to a food that was already teeming with beneficial bacteria. You can drink your double fermented kefir as is, sweeten it with some honey or maple syrup, or add it to a kefir smoothie for an ultra fruity experience.

What Is a Kefir Second Fermentation?

A second fermentation is when you take milk kefir that has been fermented with grains for a single round, and ferment it for a second time. This is also known as a double ferment, and creates a mild and slightly bubbly result. If done without adding any fruit, it further reduces the sugar and net carb content, making it more suitable for diabetics or those who need to eat a low carbohydrate diet.

Most often, a second fermentation is done to add flavor through the addition of fruit and other flavorings. This process also introduces a small amount of natural sugar, which feeds the kefir and tends to produce some additional activity (AKA bubbles), as well as a more mild flavor.

The Benefits of a Second Fermentation

There are many benefits to adding the step of a second fermentation to your kefir making process. Here are just a few:

• Added flavor
• Reduced sugar and carbs
• A boost in probiotics (AKA beneficial bacteria)
• Color
• Milder flavor
• Added fiber from the fruit
• More palatable for drinking

You Will Need

• Milk kefir: You can use either homemade kefir (check out my tutorial for making milk kefir at home), OR store bought kefir. If using store bought, be sure to purchase one that contains active cultures, and is unflavored and unsweetened.
• Fruit: You can use (almost) any fruit you would like to flavor your milk kefir with. There are certain fruits that react poorly with milk when fermenting (pineapple, mango, and kiwi), but most fruits will work great.

Equipment Needed:

• Glass jar: Whatever jars you use to make your milk kefir, you can use for a second fermentation as well. Just make sure there is enough room for both your kefir and ⅓ cup to ½ cup of chopped fruit.
• Non reactive spoon: For stirring the fruit in. You can use plastic, silicone, or wood.

How to Do a Second Fermentation of Milk Kefir

To get started, pour your milk kefir into a clean jar that is large enough to hold both the kefir, as well as the added fruit.

Then, add your fruit of choice to the jar. Chopped, small pieces of fruit will infuse more easily, and so I recommend that all larger fruit be chopped into pieces that are 1" or smaller.

Stir the strawberries into the kefir just until they are fully submerged.

Add a lid to the jar, and set aside in a warm spot on your counter out of direct sunlight. Ferment for 4-12 hours.

How long you ferment your flavored kefir will depend on how warm your house is. It will also depend on how high the sugar content is of the fruit you're using. You will need to watch your jar, looking for signs that the kefir is fermenting.

In very cold homes, you may need to ferment for up to 24 hours. Very warm homes may be as little as 4 hours.

Signs of fermentation include:

• Bubbling
• Thickening
• Pockets of whey forming
• Excess air in the jar (pickle pipes expand, and two piece lids bubble up slightly)

Once you spot some pockets of whey forming, it's a pretty safe bet that your have completed your milk kefir second fermentation. You can transfer the doubled fermented kefir to the fridge as is, or blend it to flavor the kefir with the infused fruit.

Once you've added flavor to kefir by doing a second fermentation with fruit, the shelf life shortens a bit. Try to use your kefir within one week of completing the second ferment.

Separation: A Sign of Over Fermentation

If you have allowed your kefir to ferment for too long, it will become over fermented. As long as you didn't leave it out for days, your finished kefir should still be safe to drink.

You will know that it has fermented for too long if you see a clear separation of whey and kefir. In the photo above, you can see a clear line of where the whey has separated out. In a jar that has fermented for even longer, you will see a very clear whey that may take up as much as half of the jar.

There is nothing harmful about this separation, and it can happen very quickly if your home is very warm OR if you have added fruit with a high sugar content.

What do I do if my milk kefir has over fermented?

If your kefir has over fermented, you can do a few things.

1. Strain off the whey and make a sort of kefir cheese with the curds (this works best for plain kefir, rather than flavored).
2. OR you can drink it. Separated kefir is perfectly fine to use in smoothies, or drink on its own, even though it may be on the sour side. Shake it vigorously with a lid, and the layers should combine easily. Place in the fridge, and shake again before using in a kefir smoothie.

Flavoring Kefir with a Second Fermentation

There are several ways you can flavor your milk kefir. One involves making a kefir smoothie with your flavoring of choice, and another is through the process of fermentation. The fermentation method is known as a second fermentation, and creates a drinkable, flavored kefir that can either be sweetened or unsweetened.

If you are planning on sweetening your milk kefir, I recommend that you do so after the second fermentation has been completed. This is because the sugar content of sweeteners can cause rapid and unpredictable fermentation.

Here are a few of the most common flavors added through the secondary fermentation:

• Strawberries: Add ⅓-1/2 cup of chopped fresh or frozen strawberries for every 2 cups of milk kefir.
• Blueberries: Add ¼ cup of wild blueberries, or ½ cup of cultivated blueberries for every 2 cups of kefir. You can use fresh or frozen, according to your preference.
• Banana: Use a half of a large banana, cut into slices, for every 2 cups of milk kefir.
• Lemon: Add ½ of a lemon, peel included, for every 2 cups of kefir. Cut into slices or quarters.
• Fruit: Any fruit that does not react poorly with milk can be used. ⅓-1/2 cup of 1" pieces is a good guideline when making substitutions.
• Honey: Because of rapid fermentation, I would not recommend that you include honey prior to fermentation. Instead, sweeten your kefir with honey after and refrigerate immediately.
• Chai Tea: Add 1 chai tea bag (staples removed) for every 2 cups of liquid.

Using Frozen Fruit

If you would like to use frozen fruit to double ferment your kefir, you can absolutely do that! Frozen fruit contains as much sugar as fresh fruit, and makes a great option for adding flavor and color to your homemade beverages.

Select frozen fruit that is small in size, like wild blueberries or chopped or sliced fruit. These will thaw more quickly and infuse the ferment with more flavor, more quickly.

Once the second fermentation is completed, blend the kefir with the fruit. Store in the fridge for 3-4 days, for a maximum of 1 week.

Frequently Asked Questions

Kefir Smoothie Recipes

• Mango Pineapple Kefir Smoothie
• Strawberry Kefir Smoothie
• Peanut Butter Banana Kefir Smoothie
• Green Kefir Smoothie
• Blueberry Oatmeal Kefir Smoothie
• Mango Banana Kefir Smoothie - Walder Wellness