Water Kefir: Can I Ferment in Plastic Bottles?

Perfectly fizzy and bubbly water kefir is amazing, and you need to bottle it somehow. If you are reading this, you probably want to use a plastic bottle (maybe from water or soda) that you have in your house but are not sure if it is safe to do so.

So, can I ferment water kefir in a plastic bottle? The short answer is, you can, but it shouldn’t be your first choice. Ideally, if using plastic bottles, they should be able to contain acidic liquid without degrading and releasing chemicals/BPA and have no scratches that would increase the danger of unhealthy bacteria being in touch with your water kefir.

There are many variables affecting this subject, and this is a topic that divides the fermentation community. I will tell you both sides of the story, so you can decide on which side you are on. First, I will tell you the arguments for who defends the use of only glass bottles, and then I will explain the side of those who prefer plastic.

If you’re in a hurry, here’s a summary of what will be discussed:

Against Plastic BottlesPro Plastic Bottles
Can release chemicals in the water kefir, if not able to contain the acidic environment.Choose a bottle that is made to contain acidic liquids.
Can have scratches that could harbor bad bacteria.Use new bottles and replace them after a few cycles of fermentation.
Could have BPA and release it in your water kefir.Use bottles made from BPA-free plastic.
They are almost explosion safe.
You can see how carbonated the beverage is.

What is The Problem With Plastic Bottles for Water Kefir?

Now, there are 3 main problems when using a plastic bottle for water kefir:

  • The acidic liquid can deteriorate the plastic
  • If it has any scratches
  • BPA vs BPA-free plastic

I will get into detail about each of them to help you understand the problem. If you are already aware of it, scroll to the next topic.

The average pH level of the water kefir is 4.5, which is pretty acidic. Even though this is a normal, natural pH for kefir, that is supposed to be acidic so the healthy bacteria in it can thrive, some plastics are not made to contain acidic liquid and might react with the acid and/or be corroded by it, so it could release chemical products on your water kefir. We definitely do not want that!

The second problem is that if the plastic has any scratches in it, you could expose your water kefir to unnecessary risks (no pun intended), like unwanted bacteria that could “live” inside those scratches.

And now the most popular one: BPA.

BPA stands for bisphenol A. BPA is an industrial chemical that has been used to make certain plastics and resins since the 1960s. […] Some research has shown that BPA can seep into food or beverages from containers that are made with BPA. Exposure to BPA is a concern because of possible health effects of BPA on the brain and prostate gland of fetuses, infants and children. It can also affect children’s behavior. Additional research suggests a possible link between BPA and increased blood pressure.

Mayo Clinic about BPA

This means BPA is bad, even though it is legal. If using a plastic bottle, avoid the ones made with plastic that contains BPA.

Why Should I Use Plastic Bottles for Water Kefir Second Fermentation?

We have already talked about the problems with plastic bottles. However, as I said before, there are people that advocate for them. Before getting into the safety/chemical side of this discussion, I want to talk about the two practical advantages of plastic bottles when fermenting water kefir.

First, during the second fermentation, CO2 is produced, which elevates the pressure inside the bottle. If you don’t “burp” it often (open the tap just a bit to release the pressure), glass bottles can explode. Some soda plastic bottles are more resistant to pressure than champagne bottles and, even if they explode, you won’t have glass spread all around.

Second, it is easier to see how fizzy and how much pressure you have inside by just pressing it on the sides. If there is a lot of carbonation and pressure, the walls of the bottle will be harder and you won’t be able to squeeze it as much.

Ok, so there are advantages, but what about all the “bad” stuff on the previous topic? That means that the bottle, to be safe, has to be BPA-free, have no scratches inside, and be able to contain acidic liquid. Here’s what you need to know to be able to check if your bottle is good to go.

In this article, I talked in more depth about the different kinds of plastics and the regulation of the FDA on them, so if you want a deeper understanding, check it there. But, for now, I will write a summary of what is relevant to plastic bottles when it comes to making water kefir.

When choosing a plastic bottle for water kefir, you need:

  • A bottle that was made to hold acidic liquid (that is a yes for soft drinks bottle and a no for water bottles).
  • A new bottle, not scratched or smashed, so you have no hiding places for “bad” bacteria.
  • A BPA-free bottle.
  • A bottle that was not used to contain any chemical products.
  • An FDA Compliant plastic.

For a plastic to be FDA Compliant, it has to also be Food Grade and Food Safe.

Food grade means that the material is either safe for human consumption or it is okay to come into direct contact with food products.


Food safe means that a food-grade material is also suitable for its intended use and will not create a food-safety hazard.

ISM Website

A little reminder is that plastic is only considered food grade/safe if it is being used for the purpose it was intended to. For example, an ice cream container is supposed to be used in cold temperatures for non-acidic food. So, it won’t be considered food safe for hot soup.

Applying this knowledge to the water kefir bottle situation:

If you want to ferment in a plastic bottle, just make sure it is a Food Grade Plastic, is BPA-free, and was made to retain acidic liquids.

Soda bottles are made to contain acidic liquid, water bottles are made to contain pH-neutral liquids.

You can use the table bellow as reference to the pH of acidic substances that can come in plastic bottles. If in doubt, always check the label for this information.

Tomato Juice4.30
Orange Juice3.69
Pineapple Juice3.20
Grape Juice2.90

How to Know if a Bottle is Food Grade/BPA-free Plastic?

  1. Look for the recycling symbol. It is a triangle with a number inside of it, that corresponds to the type of plastic. The number between 1 and 7 are in the food-grade range.
  2. If not sure what the bottle was made/used for, look for the food-safe plastic sign, which is a wine glass and a fork.
  3. In general, plastics with BPA are under the number 7 in the recycling category. There is no symbol for it, but sometimes it is written “BPA FREE” on the label or with the other symbols.

My View on All This

My dad likes to use a plastic bottle for water kefir and has been doing so for a while. I prefer glass bottles and I have that feeling inside me that plastic bottles are not the safest, but to be honest, I can’t prove it to you and in theory, you can avoid the problems that are the main concerns with plastic bottles. But if I go to my dad’s, I will drink his amazing pineapple water kefir “champagne” that he prepared in a plastic bottle.

If you go on Reddit and see the discussion on this subject, you see that both sides have valid arguments and in the end, you have to decide what is more suitable to you and your beliefs.

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