Why Is My Kefir Bitter?

Kefir is one of the most delicious and probiotic-rich drinks out there. I like to drink mine just before bed to get a really relaxed good-night sleep. But lately my kefir started tasting kind of bitter and I wondered why.

So, I did some research, and here is why kefir tastes bitter: Bitter kefir is a sign of over-active yeast during the fermentation process. If the ratio of yeast and good bacteria is out of balance your kefir will have a bitter taste.

Luckily this is quite easy to fix and in this post, I’ll cover the most common ways to fix bitter kefir. I’ll cover in a bit more detail what exactly causes bitter kefir. So, let’s get into it!

Should kefir be bitter?

Kefir should not be bitter. A sour taste is quite normal but bitterness usually means there is something out of balance in the fermentation eco-system. When storing kefir in the fridge for too long it may take on a slightly more bitter taste than usual but the sourness should always be more prevalent.

My first batches of kefir also turned our rather sour and bitter and I was wondering what I did wrong. It can be hard to tell if your kefir has turned out good or bad especially if you’ve never tasted great kefir before.

I’ll try my best to describe what really good kefir should taste like!

What should kefir taste like?

Kefir should taste slightly sour – sort of like sour milk. The consistency should be a bit thicker than regular milk – more like buttermilk. I can be a bit lumpy or chunky so stirring your kefir before drinking will even out the flavors a bit.

That said, there are many ways to make and enjoy kefir. Even kefir that is just like plain milk or extremely sour is fine to drink. The taste lets us know how far the fermentation process has come along.

After 12 hours kefir will just taste like slightly thickened milk but will not have that sour touch yet. 12-24 hours are my regular fermentation time and kefir should have a distinctly sour taste after successful fermentation.

However, kefir should not be bitter. Bitterness is a sign that something has gone wrong during the fermentation process. Let’s look at why your kefir is bitter and how to fix it!

What causes kefir to taste bitter?

High acidity, over-active yeast, and some other external conditions can all contribute to the bitterness in kefir. A bitter taste in kefir can have multiple causes. I’ve compiled this of the most common causes of bitter kefir:

  • Over-active Yeast: Bitterness is usually a sign of high acidity. This is caused in kefir by over-active yeast. The lactic acid-producing bacteria and the yeast live in a delicate balance in kefir grains. Any upset in this balance can result in a poor fermentation process and a bitter taste.
  • Excessive Heat: Finding just the right temperature to ferment your kefir at is no easy task but standard room temperature should work just fine. If your kefir tastes bitter make sure it has not been exposed to excessive heat (e.g. next to a heater, direct sunlight) during fermentation.
  • Long Refrigeration: In some cases, long refrigeration times can cause some bitter taste in kefir. Sometimes I had my kefir in the fridge for over a month and the taste definitely deteriorated over time.

It can be hard to tell what exactly causes your kefir batch to turn out bitter but examine any of the three possibilities above. Perhaps you’ll find some clues there. In any case, let’s see how we can get your next batch of kefir to taste delicious!

How to fix bitter kefir

Preventing bitter kefir and getting fermentation conditions just right is actually much easier than it sounds. Try any of these troubleshooting tips to make your kefir less bitter and more enjoyable.

  • Rinse With Milk: One of the gentlest ways to restart your kefir grains on a new batch after the first has turned out too bitter is to rinse them with milk. This will remove the excessive yeast from the surface while preserving the delicate layer of microorganisms.
  • Wash With Filtered Water: If rinsing with milk doesn’t do the trick the next would be to use filtered water. Cleaning your grains with water is much harsher since the H2O strips the kefir grains of their protective coating. However, it can be a great way to reboot the fermentation process.
  • Colder Environment: Perhaps the bitterness was just caused by high temperatures and you’ll need to find a cooler spot in your home. Especially in summer, this can be a challenging task if you don’t have a basement. I keep mine in the coolest room of the house, in the shade with no exposure to sunlight.
  • Add More Lactose: Since bitterness is a sign of yeast taking over during the fermentation process we can add more milk from the start to counteract this. When there is more lactose for the bacteria to digest they will be able to keep the yeast growth in check.
  • Drink It Fresh: Sometimes a bitter taste can also stem from over-refrigeration. Keeping your fermented kefir in the fridge for too long can deteriorate taste. I like to drink my kefir fresh or after just a couple of days in the fridge!


Bitter kefir is not something you should have to put up with. It’s usually a sign of the yeast taking over the delicate balance of microorganisms in kefir. Luckily, there are some simple solutions to this.

Every time my kefir has not turned out the way I had hope, I usually just start over by rinsing the grains with milk and setting up a new batch. If you get most of the conditions right your kefir should turn out just fine with a slightly sour taste.

That’s when you know you’ve it right 😉


  • Hi, I'm Marvin! In early 2019 I started fermenting sauerkraut, kefir, and kombucha and noticed the incredible health benefits that came with it. I was less irritated, had fewer allergies and my skin got better. I started this blog to share how fermented foods have helped me and how simple they are to prepare! Look around and see what speaks to you and all the best on your fermentation journey!

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