How to make sauerkraut: the ultimate guide

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Estimated reading time: 38 minutes

This is a complete guide on how to make sauerkraut at home, in a glass mason jar or crock. Are you’re a beginner? Then, you’re in the right place! If you’ve been making it for a while, but are failing, keep reading. This isn’t a quick 10 step guide. Instead, you'll deeply understand how cabbage fermentation works. When that happens, your fermentation confidence will skyrocket! You’ll have much more success making sauerkraut.

You’ll start looking at fermentation as a home science experiment instead of a ‘recipe’. By doing that, you’ll understand what’s gone wrong in the past. Your days of throwing cabbage in a jar and ‘hoping’ for the best are about to end!

We’ll discuss 

• salt
• mold and yeast
• acidity
• temperature
• safety, and
• the equipment used
• . . . and more!

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I’ll share a secret with you.

Learning how to make homemade sauerkraut isn’t hard. Anyone can do the basic steps.

You might fail, though. But it’s not your fault.

Why not?

You’ve never gotten a simple explanation of fermentation.

Maybe you’re a missing a step somewhere, but can’t put your finger on it.

To make things worse, you can’t see the inner workings of fermentation with your naked eye.

You can see sauerkraut’s color change, see mold or yeast, and even smell it. But fermentation is mostly microscopic. And that, you can’t see.

A batch of homemade sauerkraut can take up to 6 weeks to ferment. You waste 6 weeks of patience if things go wrong.

Bet you can’t wait to give it another try!

Yeah, not so much.

But you should.

The art of making sauerkraut at home is not a recipe. It’s a science experiment in your home.

I’ll make sure you understand the basic biology, chemistry, and physics — explained in a way that’s not a science class.

. . . everything you need to be successful.

Your success is important to me.

How does that sound?

Are you ready to get started?

What is Sauerkraut?

Sauerkraut is fermented cabbage.

Simple, right?

It’s raw cabbage that’s gone through fermentation.

But what is fermentation?

Well, it’s food preservation.

Preservation occurs with help from

• acid-producing bacteria
• salt, and
• an oxygen-free environment

Then, you control the temperature and let time pass.

Dangerous microorganisms rarely survive fermentation (if you do it right).

In contrast, lactic acid bacteria survive. So, you’ll wind up eating them.

They end up in your digestive system — your stomach and intestines — which can help you stay healthy.

How Cabbage Fermentation Works — The Overview

Fermenting cabbage preserves it.

OK great, but how?

You’ll find it easier to understand if we start at the end. So, let’s skip to finished sauerkraut.

The main preservative in finished sauerkraut is acid.

Disease-causing bacteria and viruses (called pathogens) don’t grow in fermented cabbage because of this acid.

But the acid must be strong enough.

How strong?

The acidity needs to be below pH 4.0. But you’ll need to know what a pH scale is.

All in due time.

There’s an easier way to think of it…

Let’s use two familiar foods for comparison.

Sauerkraut’s acid strength is halfway between lemon juice and coffee.

When you taste either coffee or lemon juice, each tastes sour. Sourness is a characteristic of acidic food. Coffee is mildly acidic, so it barely tastes sour. It’s subtle. You may not even notice it because coffee’s flavors mask the sourness.

In contrast, lemon juice is a stronger acid. It’s tastes very sour. Lemon juice is near stomach acid on the pH scale.

Sauerkraut sits in-between lemon juice and coffee. It’s more sour than coffee, and less sour than lemon juice.

OK, we know acid is the end game. Now, let’s rewind further.

What creates the acid?

Lactic acid bacteria create it by eating cabbage sugar.

What else do lactic acid bacteria do?

They create carbon dioxide gas.

Oxygen spoils vegetables, while carbon dioxide preserves them.

OK, what about salt? How does that work?

Salt does a few things.

• Salt kills some pathogens.
• It controls the growth of lactic acid bacteria.
• It prevents mushy sauerkraut.

When you add salt, it pulls water out of your cabbage. Then, salt mixes with water creating brine.

What’s the purpose of brine?

It protects your sauerkraut.

You won’t find oxygen below the brine’s surface.

And, pathogens do poorly without oxygen.

In contrast, lactic acid bacteria do great without oxygen.

Imagine being able to hold your breath underwater for four weeks with a thumbs-up and a smile. Lactic acid bacteria do this all the time.

Where do lactic acid bacteria come from?

They’re found naturally on cabbage leaves. When you bring a cabbage home, it comes pre-equipped with bacteria thanks to nature.

Let’s do a quick recap. Instead of the end in mind, we’ll start from the beginning.

1. Lactic acid bacteria are on cabbage leaves at harvest time.
2. You bring the cabbage home and shred it.
3. Mixing salt into the cabbage makes salty water.
4. The cabbage sits under the salty water, keeping oxygen out.
5. Lactic acid bacteria eat cabbage sugar, create acid and carbon dioxide gas.
6. Acid gets stronger and stronger until you have safely preserved sauerkraut.

So, that’s the simple explanation of cabbage fermentation. There’s more to it. But we’ll dive deeper as you read.

The Four Secret Weapons Used to Make Sauerkraut

To stop pathogens, you need four layers of protection. I call them Sauerkraut’s Four Secret Weapons™. They work closely as a team. These weapons keep your fermented cabbage safe to eat.

The four secret weapons are:

• Salt
• Acid
• A lack of oxygen
• Lactic acid bacteria

Let’s get better acquainted with them, shall we?

Salt

Pathogens ruin your sauerkraut.

And, some pathogens can’t survive in salt.

So, what do we do?

We add salt to our arsenal of weapons.

What about the good lactic acid bacteria? Will salt harm them?

No.

Lactic acid bacteria are halotolerant.

Halotolerant means to live happily in salt.

When adding salt, water seeps out of your cabbage. That’s called osmosis. As salt dissolves in that water, a saltwater solution forms called brine. Brine is salty water.

As well, salt protects pectins (a starch) in your cabbage, which helps keep it crunchy. This prevents mushiness. When you look at cabbage under a microscope, you see pectins giving tiny cabbage cells structure, keeping them rigid.

Moreover, salt controls lactic acid bacteria’s growth.

If you use more salt, it slows their growth. Conversely, using less salt speeds up their growth. The faster they grow, the faster your homemade sauerkraut will ferment.

Acid

Pathogens hate acid. They rarely survive in it.

So, what do we do?

We include acid in our arsenal of weapons. Fortunately, lactic acid bacteria are fine with acid. In fact, they make it themselves. So, you don’t need to add your own acid, like vinegar.

As well, acid makes your sauerkraut taste sour.

A Lack of Oxygen

An oxygen-free environment makes it hard for some pathogens to survive.

No oxygen, no survival.

So, let’s add an oxygen-free environment to our list of secret weapons.

The scientific way of saying “without oxygen” is anaerobic.

But what about our lactic acid bacteria friends?

What happens to them if there’s no oxygen?

As lactic acid bacteria say, “No oxygen, no problem!”

Like your muscles, lactic acid bacteria can create energy from sugar without oxygen.

So, how do we create an oxygen-free, anaerobic environment?

Three things create an anaerobic environment.

First, oxygen-loving microbes quickly use up any oxygen in your brine. These microbes could be pathogens, fungi, bacteria, or yeasts. Don’t worry, they die once the oxygen is gone.

Second, lactic acid bacteria create carbon dioxide gas.

Third, the brine makes a barrier atop your cabbage. If your cabbage sits below the brine, oxygen can’t enter.

Healthy Bacteria

Lactic acid bacteria live in your homemade sauerkraut.

Lactic acid bacteria

• are fine with salt and don’t mind living in it
• create acid when they eat, so acid doesn’t bother them
• don’t need oxygen to live and multiply

So, they’ll grow and multiply fine.

The result?

Lactic acid bacteria crowd out pathogens.

Pathogens die when healthy bacteria outnumber them.

So, lactic acid bacteria is our last secret weapon.

We’re putting serious things in place, assuring our cabbage doesn’t rot, spoil or become filled with pathogens.

We’ll have the good bacteria running the show.

Where do these healthy bacteria come from?

They’re all around us on

• soil
• vegetables
• fruits
• your skin

In fact, they’re on that cabbage head you’re using to make homemade sauerkraut.

And they’re not just on the outer leaves. They’re on every leaf to the cabbage’s core.

Fermentation Secret Weapon Recap

Let’s do a recap of our of secret weapons. They are

• Salt
• Acid
• A lack of oxygen, and
• Lactic acid bacteria

Together, Sauerkraut’s Secret Weapons™ lay the foundation for making successful sauerkraut at home.

The Three Stages of Sauerkraut Fermentation

There are three stages of cabbage fermentation.

The first stage foreshadows fermentation. So, we’ll call it the shadow stage. Fermentation is not happening yet at this stage.

Believe it or not, pathogens are helpful during the shadow stage.

Later on, lactic acid bacteria take over.

To make it simple, we’ll just discuss the big three bacteria. They are

• Leuconostoc mesenteroides
• Lactobacillus brevis
• Lactobacillus plantarum

Leuconostoc mesenteroides does its job during the second stage.

Lactobacillus brevis and Lactobacillus plantarum do their jobs in the third stage.

Each stage has a different purpose.

First Stage - The Shadow Stage

There’s a stage that foreshadows fermentation. So, we call it the shadow stage.

The shadow stage involves oxygen-loving

• pathogens
• bacteria
• yeast, and
• fungi

The brine in your mason jar is mostly made of water. And water contains dissolved oxygen. You may have heard water called H₂O before. The ‘O’ part means it contains oxygen. ‘O’ for oxygen.

Soon, aerobic microorganisms, the ones that like oxygen, start growing.

They consume oxygen until it’s gone. Then they die.

Because of this, your homemade sauerkraut is now oxygen free.

That’s pretty cool. Fermentation hasn’t even started yet!

This oxygen-using stage has a scientific name, too . . .

It’s called aerobic respiration. Aerobic means ‘with oxygen’.

Aerobic respiration happens when microbes make energy from oxygen.

In contrast, fermentation happens without oxygen.

After aerobic respiration is done, fermentation takes over.

Second Fermentation Stage

The second stage involves bacteria named Leuconostoc mesenteroides.

They multiply quickly during the first few days of fermentation.

Leuconostoc mesenteroides multiply quickly because they

1. can handle many salt concentrations.
2. are OK with wider temperature swings than other bacteria.

They eat sugars found in your cabbage, then create

1. lactic acid
2. acetic acid
3. ethanol (alcohol)
4. carbon dioxide
5. flavor compounds

But, Leuconostoc mesenteroides have a limit to the acid level they can handle. Once the acid is strong enough, they will die. Then, other bacteria take over.

In the third stage, we’ll discuss how Lactobacillus brevis and Lactobacillus plantarum steal the show.

Third Fermentation Stage

The third stage involves two bacteria species. They are

• Lactobacillus brevis
• Lactobacillus plantarum

They can cope with strong acid. By eating cabbage sugar, they make even more lactic acid. But, they don’t make carbon dioxide.

By the end of this stage, your sauerkraut becomes acidic enough to prevent spoiling.

And like second-stage bacteria, these third-stage bacteria continue to make flavor compounds.

Human Fermentation

That’s a creepy title, right?

Bear with me.

You have more in common with lactic acid bacteria than you think. You might not realize it, but your body uses fermentation. And, it’s good at it!

First, let’s discuss how your body uses oxygen for energy. Then, I’ll point out where fermentation comes in.

Are you familiar with aerobic exercise?

You know, the kind that gets you breathing heavily, taking in lots of oxygen, like jogging. That’s an aerobic activity. It needs lots of oxygen.

On the other hand, weightlifting is an anaerobic exercise. Lifting weights requires short bursts of strength. You need to take fewer breaths. Still, you need some oxygen. So, it’s not truly anaerobic.

But, if you overwork your muscles, they run out of oxygen. This makes them anaerobic. To fix this, your body switches to lactic acid fermentation to create energy from sugar, without oxygen. This can happen after jogging or weightlifting.

As a result, your muscles make lactic acid. But it’s not used to preserve you like sauerkraut. Your liver deals with that acid, helping you make even more energy.

Fermentation happens in other parts of your body, too. Red blood cells carry oxygen around your body. But they don’t use oxygen for their own energy. They don’t have the tools to do that.

Instead, they use fermentation to make energy from sugar without oxygen. As a result, red blood cells make lactic acid. Then, your liver turns the acid into more energy.

So, your body is pretty good at fermentation. It’s not just for vegetables.

Fermenting cabbage to feed yourself seems a bit more meaningful now, doesn’t it?

Oxygen, Carbon Dioxide and You

Leuconostoc mesenteroides create carbon dioxide.

This protects your kraut from harmful pathogens.

As well, brine protects your cabbage from oxygen exposure.

Use the rhyme, “everything’s fine if it’s under the brine” to remember this.

You always want your cabbage to sit below the brine. But sometimes, carbon dioxide gas bubbles push your cabbage upwards. In this case, the cabbage will sit above the brine. This is where oxygen lurks.

Also, bits of cabbage will float to the top of the brine, exposing themselves to oxygen.

So, we’ve discovered an area that’s vulnerable to oxygen.

This area starts where the brine ends and the open air begins. It’s where unhealthy pathogens grow.

There are three tools you’ll use to reduce oxygen at the top of your mason jar. They are

• barriers
• weights, and
• seals

Barriers

You’ll use a barrier to stop cabbage bits from floating to the brine’s surface.

Three examples of barriers are a

• cabbage leaf
• food-grade plastic zipper bag filled with salty water
• plastic or stainless-steel disc

For example, a cabbage leaf placed on top of your sauerkraut acts as a barrier, keeping cabbage bits from floating upwards. These leaves cost you nothing.

A food-grade plastic zipper bag filled with salty water is another low-cost solution. The bag doubles as a weight, pushing on your cabbage.

As well, you can buy plastic or stainless-steel circular shaped discs. These discs secure themselves in place. They won’t move.

These discs also simulate a weight, holding your sauerkraut down.

Weights

The barrier we put in place stops cabbage bits from floating upwards. Sometimes, though, the brine level doesn’t sit high enough to cover the cabbage. Because of that, you need to force the cabbage and barrier downward.

When you apply downward force, the brine moves upward. It’s just like squeezing water from a sponge.

Once the brine level rises, it protects your cabbage from oxygen.

Three examples of weights are

• glass or ceramic weights
• rocks (warning below)
• a food-grade plastic bag filled with salt water

Using Rocks as Fermentation Weights

In most cases, don’t use rocks as fermentation weights. It can be dangerous.

It’s hard to tell what a rock is made of. For example, if it’s made of marble or limestone, lactic acid bacteria can react with it, leeching things into your homemade sauerkraut. If you use a rock, make sure it is acid-safe. Don’t randomly pick a rock from your back yard, local park, or a nearby rural area.

Your safest options are glass or ceramic weights. These are acid-safe.

Seals, Lids, Airlocks, and Valves

Brine is a protective layer of salty water atop your cabbage. It’s a liquid seal that keeps oxygen out. Brine is the first line of defense. You need to build upon it.

Brine’s liquid surface touches the open air. This is where yeasts and molds grow. To stop that growth, you remove oxygen.

How do we remove oxygen?

Well, we know some lactic acid bacteria make carbon dioxide gas. That gas moves upwards, bubbling through the brine, up into the open air.

Hmm, maybe we can make use of this scenario...

What if we could trap that carbon dioxide bubbling out through the brine?

Let’s keep going with this idea…

If we cover and seal the mason jar’s top, the carbon dioxide gets trapped above the brine. Then, instead of oxygen above the brine, we’d have carbon dioxide. Luckily, mold and yeast don’t grow in carbon dioxide.

This space where the carbon dioxide collects is called an airlock.

What is an Airlock?

You may know airlocks as a room astronauts use on space shuttles. You see them in movies. An astronaut enters the airlock before leaving the space shuttle into space.

That room has two doors. One door leads to the space shuttle and the other into space. So, the astronaut enters the airlock from within the space shuttle, closing the door behind them. This stops the breathable air of the space shuttle from escaping into space. When the outer door opens, the airlock’s air rushes into space.

What does that have to do with making sauerkraut at home?

That tiny room on the space shuttle—it’s the same thing as the space above your brine and below the mason jar’s lid.

That’s an airlock!

Except in our case, it’s filled with carbon dioxide.

The brine stops oxygen from entering your sauerkraut (the space shuttle).

The mason jar’s lid stops carbon dioxide from leaving into the open air (outer space).

Remember when the astronaut opens the door into space? Well, that’s like taking the lid off of your mason jar. It lets carbon dioxide escape into the open air.

Wait, don’t we need that carbon dioxide to stop mold and yeast?

Absolutely!

But here’s the problem…

You want to keep most of the carbon dioxide. But not all of it.

Lactic acid bacteria continuously make carbon dioxide gas. If you seal the mason jar tightly, that gas will build up. It’s possible your mason jar will burst open from this gas pressure. That leaves you with a big mess of sauerkraut.

So, how do you solve this problem?

You need to release a little carbon dioxide. But not too much. Just enough to stop your mason jar from exploding.

But you mustn’t let oxygen return.

To do that, your airlock needs a valve.

What is a Valve?

A valve is a tiny door. Excess carbon dioxide pushes the door open.

Once the valve lets a little carbon dioxide out, it snaps closed (like a spring). Because of this, oxygen can’t enter.

Lactic acid bacteria create more carbon dioxide, which pushes on the valve again. The valve lets carbon dioxide out, then snaps shut.

Rinse and repeat.

Eventually, lactic acid bacteria will stop making carbon dioxide. When that happens, the valve stays shut. Now you have a protective layer of carbon dioxide sitting at the top of your mason jar, above the brine, and below the lid.

Examples of Airlock/Valve Combinations

This is where you’ll easily get confused. There are many airlock or valve devices you can use when making fermented cabbage. You can buy or make them yourself.

I’ll give you a few examples. No matter which one you use, they work on the same basic idea.

Mason Jar Lid with Valve

You can find screw-top lids that have a built-in valve. The valve looks like a button. Carbon dioxide will exit the mason jar through this valve. The exit-only airflow makes sure oxygen won’t enter.

Look at the visual below showcasing a sealed lid with an in-lid valve.

Food-grade Plastic Zipper Bag

You can insert an empty plastic zipper bag atop the brine. This bag occupies the space where air normally is.

Then, you insert a second inner bag filled with homemade brine into the outer bag. This assures the outer bag holds its shape, keeping air out.

Finally, you drape the outer bag over the top of the mason jar, creating a seal.

The zipper bag setup has an airlock, too. It hides in plain sight on the upper-top sides of your mason jar.

You can place a small plate and coffee cup atop the mason jar. This puts pressure on the outer bag, tightening the seal.

Carbon dioxide pushes past the outer bag at the mason jar’s rim. This is the valve.

The food-grade plastic zipper bag setup is cheap. But you’ll have to babysit it.

The second fermentation stage creates lots of carbon dioxide gas. This forces brine upwards past the bag’s seal, spilling over the side of the mason jar. You’ll have to soak up the spills with a paper towel.

The Fermented Cabbage Process in Summary

Let’s take a holistic view of the fermentation process.

1. Oxygen-loving microbes use up all the oxygen.
2. Lactic acid bacteria eat cabbage sugar.
3. Lactic acid bacteria produce acid and carbon dioxide gas.
4. Carbon dioxide gas moves upwards.
5. Airspace above the brine gets filled with carbon dioxide gas (the airlock).
6. Excess carbon dioxide gas exits through the valve at the top of the airlock.
7. The valve and seal keep oxygen from entering your jar.

In the image above, you can see carbon dioxide gas bubbles forming in homemade sauerkraut.

Sauerkraut Flavor

Lactic acid bacteria contribute to sauerkraut’s flavor.

They create lactic acid, which tastes sour. But, they make other flavors, too.

Lactic acid bacteria make special substances, called flavor compounds.

Flavor compounds meld and combine with each other. This makes even more flavors.

The major categories of these compounds are

• sulfur compounds
• alcohols
• aldehydes
• acetals
• aromatic hydrocarbons
• volatile esters

It’s a mouthful, isn’t it?

What’s more is these flavor compounds appear in different amounts in each batch. This is for several reasons. It can depend on the

• variety of cabbage
• amount of sugar found in your cabbage variety
• conditions in which the farmer grew the cabbage, like soil and climate
• number of bacteria present on the cabbage leaves before you start
• fermentation temperature and time

What if there’s Mold on Your Sauerkraut?

A mold spore will land on your homemade sauerkraut if exposed to open air. Further, mold spores may be on your raw cabbage leaves.

Mold Below the Brine

While mold can’t grow below the brine’s surface, its hyphae (thin strands) can. It’s hard to judge how far the hyphae have extended into your sauerkraut.

Mold’s mycotoxins may find their way below the brine, too.

Scooping Mold Off Fermented Cabbage

You may read advice to “scoop off” surface mold. You remove the mold by scooping a few inches/centimeters into your sauerkraut. This is not a completely safe way of dealing with mold.

Scooping mold growth off your fermented cabbage can be risky. When you do, mold spores can accidentally get mixed into the clean sauerkraut. This starts the problem over again.

Let’s compare this to mold on a slice of bread. Your first reaction might be to cut out the green moldy part, then eat the bread. But mold hyphae have extended into your bread beyond the green part. So, don’t cut off the moldy parts of bread to salvage it. This applies to fermented cabbage, too.

Preventing Mold

Instead of removing mold, I strongly suggest spending your time preventing it. You’ll be in a better position when you’re asking, “how do I prevent it?” instead of “Oh no, I’ve got mold, now what do I do?”.

Mold needs oxygen, moisture, and an organic food source to grow. Moisture is present in the brine. And cabbage sugar is a food source.

This leaves eliminating oxygen as your best bet for mold prevention.

Focus on removing the oxygen sitting between the surface of your brine and the top of your mason jar’s lid. Using a seal, airlock, and valve is the best way to go. This prevents oxygen exposure, while allowing carbon dioxide gas to escape.

Placing a towel or cheesecloth over your sauerkraut jar won’t work. These are porous materials that allow oxygen and mold spores to flow through them.

Further, make sure you clean your mason jar, lid, and weight with warm soapy water before you ferment.

Health Effects of Moldy Sauerkraut

There are historical anecdotes of sauerkraut makers stirring mold back into their fermented cabbage because they enjoy the taste. As the story goes, these people remain perfectly healthy. What you don’t hear is that mold can take its time causing health effects in the stomach. It can take multiple exposures of eating it. So, the health effects won’t happen overnight.

Moreover, mold may cause allergy-like or irritant effects in some people. If you have no known reactions to mold, repeated exposure may change that.

Most people have no obvious reactions to eating small amounts of mold. But, mold is not safe to eat.

Period.

There’s no shame in throwing your sauerkraut out and starting over.

Preventing and Removing Kahm Yeast

It’s unlikely you’ll stop yeast growth completely.

But you’ll control it, reducing its growth.

Kham Yeast is non-toxic. But, it can cause flavor and odor issues.

Kahm Yeast isn’t a single yeast species. It’s a growth of many yeasts. And, they eat sugars found in your cabbage. As far as food goes, they have plenty of it.

If they have lots of food, how can we prevent yeast?

Take oxygen away from them.

Kahm Yeast grows faster with oxygen. And there’s a risk of oxygen exposure at the top of your mason jar.

To prevent Kahm Yeast, your best bet is to remove oxygen between your brine’s surface and the mason jar’s lid. If you’re using a barrier, weight, and a sealing lid that vents excess carbon dioxide, you’ll be ok.

In fact, the prevention techniques for mold are the same for yeasts.

You may still get yeast growth, though.

If that happens, you can safety scoop it off since yeast doesn’t grow roots.  So, don’t worry about it growing deep into your sauerkraut.

Here’s a simple trick to remove Kahm yeast… Gently lower a paper towel on to the yeast’s surface. Then, pull up the paper towel. The yeast will stick to the paper towel.

Opening Your Sauerkraut Mason Jar or Crock Too Often

You’ll find plenty of advice to taste test your sauerkraut now and then as it ferments. That advice tells you that your fermented cabbage is ready when it tastes the way you like it. But, every time you open that lid, air enters, putting your homemade sauerkraut at risk. Yeasts and mold spores live in that air.

Alternatives to Opening Your Mason Jar

Start Two Batches

If you need to taste often, start two batches, each in a separate jar.

Don’t open the first jar. This keeps oxygen out. But, you’ll open the second jar to taste often. If the tasting-jar is successful, great. If it’s covered in mold and yeast, throw it out. That’s OK because the unopened mason jar will be mold and yeast-free.

Multiple Batches with Different Fermentation Times

There’s a method designed so you don’t open any mason jar during fermentation. To make this work, you’ll need to ferment multiple batches at once.

Each jar’s batch will end at different lengths of time. At two weeks, three weeks, four weeks, and so on. Don’t open them until the time elapses. This lets you taste test the fermentation duration you prefer the most.

Fermentation Temperature, Time, and Salt

Salt Amounts and Fermentation Time

Salt affects fermentation times. Using lots of salt slows fermentation. Less salt speeds it up.

Lactic acid bacteria are halotolerant, meaning they survive in salt. But that doesn’t mean they are salt-proof. Salt will still affect them. Less salt will make bacteria multiply faster. In contrast, more salt slows them down.

How Much Salt Should I Use?

I recommended using a salt concentration of 2% salt by weight of your cabbage.

Why 2%?

The accepted range is between 1.5% and 2.5%.

2% is right in the middle.

When starting out, I always recommend 2%. It’s a safe place to start. It’s not extreme on either end of the spectrum.

After you create successful homemade sauerkraut with 2%, then you can change the salt concentration. Get experience under your belt first.

Can’t I just start with 1.5%?

Sure, you can.

But please don’t.

It makes it harder for you to get the fermentation time just right. 1.5% will make bacteria multiply faster. So, you’ll have to pay closer attention to your room temperature to control runaway bacteria growth.

If you’re dead set on using 1.5%, get a couple batches of 2% done and out of the way. Then give 1.5% and 2.5% a try. It’s easier to try different salt concentrations after you have experience with the baseline 2%.

Making homemade sauerkraut is a science experiment in your home. So, you’ll want to apply the scientific method. Test things out at 2%. Then, write down

• the room temperature you used
• the length of fermentation time
• how it tasted

Then, when trying 1.5%, make notes for that too and compare it to your 2% notes. This helps you learn quickly.

The Right Temperature for Making Homemade Sauerkraut

A good temperature for making homemade sauerkraut is between 16°Celsius to 21° Celsius (60°Fahrenheit to 70° Fahrenheit).

Cabbage takes three to four weeks to ferment in this temperature range.

But, this assumes you’re using a 2% salt concentration.

Does that mean I can’t make fermented cabbage if it’s warmer or colder in my home?

There are limits to the room temperature you can use. Fermentation happens quicker when it’s warm and slower when it’s cold.

If your room temperature is extremely hot, such as 40°C (104°F), bacteria growth will run away on you. Your sauerkraut won’t taste good either. Conversely, if it’s below 12°C (54°F), bacteria may not grow.

Fermenting Cabbage in Cool Temperatures

Let’s say your room temperature is 12°C to 16°C (54°F to 60°F). This is the lowest temperature for making fermented cabbage. The time it takes for cabbage to ferment in this range is around four to six weeks (using 2% salt). As you drop to 11°C (54°F) and below, lactic acid bacteria barely multiply, stopping fermentation.

Fermenting Cabbage in Warm Temperatures

Let’s look at the high-end temperature range. Let’s say your room temperature is 25°C to 28°C (77°F to 82°F), but not higher. Taste tests showed it’s less than ideal. This is because the flavor compounds don’t fully develop.

Leuconostoc mesenteroides grows poorly above 21°C (70°F). Because of this, you’ll miss out on the flavor it makes.

The time it takes for cabbage to ferment in the high-end temperature range is near 7 days (using 2% salt). If you have no other choice of temperatures, go ahead. But your success may vary.

The Ideal Fermentation Temperature

In a perfect world, your ideal fermenting temperature is 18°C (64°F). It’s well above the 12°C (54°F) minimum, removing risks of stalling bacteria growth. Also, 18°C (64°F) gives you wiggle room up to 21°C (70°F). Higher than 21°C (70°F) may affect Leuconostoc mesenteroides’ performance.

Fermentation Time Table

Here is a table with temperatures and duration for making homemade sauerkraut using 2% salt:

Temperature (Metric)	Temperature (Imperial)	Time
0°C to 11°C	32°F to 52°F	Forever
12°C to 16°C	54°F to 60°F	4 to 6 weeks
16°C to 21°C	60°F to 70°F	3 to 4 weeks
22°C to 24°C	72°F to 75°F	10 to 14 days
25°C to 28°C	77°F to 82°F	7 to 10 days

Is Homemade Sauerkraut Safe to Eat?

Science tells us fermented cabbage is safe to eat (if made properly). In fact, it’s safer than eating raw fresh cabbage. This is because of sauerkraut’s

• salt content
• acidity
• anaerobic (oxygen-free) environment
• lactic acid bacteria

Acidity is the main reason fermented cabbage is safe to eat. When the pH level drops to 4.0 and below, it’s rare for pathogens to take hold. In contrast, fresh vegetables are riskier to eat because they don’t have acid protection. We rinse our vegetables before eating. But that’s not a guarantee the pathogens rinsed away. They may be present at the start. But, after fermentation is complete, acid kills them.

Pathogenic Bacteria in Your Sauerkraut

Pathogens are bacteria or viruses that cause disease.

The most common food-borne pathogens are

• E. coli O157:H7
• Norovirus
• Salmonella
• Listeria
• Cyclospora

Another is Clostridium botulinum which causes Botulism in people.

It’s possible any of these live on raw cabbage leaves.

What Kills those Harmful Pathogens?

What is pH?

You’ll notice the terms ‘acid’ and ‘pH levels’ when reading about fermentation.

Let’s explore them.

pH are two letters that stand for “Potential of Hydrogen”. It relates to hydrogen ions. Scientists created a scale of numbers from 0 to 14 to measure pH.

When a substance is very acidic, the scale will read “0”. When a substance is very non-acidic, the pH scale reads “14”. The number 7 sits in the middle. It’s considered neutral, neither acidic nor non-acidic.

Any number below 7 is on the acidic side. The lower the number below 7, the stronger the acid is. Numbers above 7 are on the alkaline (non-acidic) side. The higher the number above 7, the more alkaline.

A good example of neutral is plain water. Water reads pH 7 on the scale. Lemon juice reads near pH 2.5. Stomach acid reads near pH 2.0.

Sauerkraut, when finished fermenting, should read near pH 3.0 to 4.0.

The lower the pH, the better at killing pathogens.

For example, stomach acid is somewhere between pH 1.0 to pH 3.0. We consume pathogens more often than you think. Our stomach acid kills them.

The opposite is true. When something reads far above pH 7, pathogens die, too. For example, household bleach measures at pH 13, It’s extremely alkaline. It’s known for killing viruses on surfaces. This is because many organic organisms prefer a neutral pH of 7. For example, the human body has a pH just above pH 7.0.

Acidity Provides the Most Protection

Most pathogens don’t survive if the pH is 4.0 or lower. Properly made homemade sauerkraut can have a pH of 3.0 to 4.0.

But isn’t the safe minimum pH for fermented cabbage pH 4.6?

No. Not if you’re learning how to make sauerkraut at home.

pH 4.6 is only safe if fermented cabbage is raised to a very high temperature for a short time. That’s called pasteurization. It kills all microorganisms . . . good or bad. That includes lactic acid bacteria. Commercial food makers follow strict laws on this.

For food making businesses, laws in some areas say acidified or fermented foods need an acidity of pH 4.2 to pH 3.3 or lower.

If you’re learning how to make sauerkraut at home, you’ll be right in that range. Your final pH will be 3.0 to 4.0. Well below pH 4.6.

You’ll find other suggestions that say anything less than pH 4.6 is OK. But, I disagree. Escherichia coli, for example, can survive at pH 4.0. Below 4.0, it dies.

A Lack of Oxygen Doesn’t Kill Every Pathogen Species

Did you know pathogens can survive with or without oxygen? It depends on the species.

Clostridium botulinum survives without oxygen.

As well, Escherichia coli likes oxygen, but doesn’t need it.

But, Bacillus Cereus will die without oxygen.

So, removing oxygen from your sauerkraut is important, but it won’t give complete protection.

Salt in Sauerkraut Won’t Kill Every Pathogen Species

Ever read that pathogens can’t survive in salt?

Nonsense.

Clostridium botulinum tolerates up to 5% salt. Sometimes, up to 10%.

So, a 2% salt concentration is of no use in this case.

But, Campylobacter jejuni suffers in salt concentrations above 1%.

So, a 2% salt concentration is helpful here.

When you’re told that salt will kill pathogens in your sauerkraut, take it with a grain of salt.

It Takes Teamwork

Our secret weapons act as a team to make fermented cabbage safe to eat. If one is missing, it jeopardizes the safety of your homemade sauerkraut.

Any one secret weapon from our arsenal won’t kill every pathogen species. Although, acid comes close. But only when the pH level drops below pH 4.0.

It’s like war.

Every soldier has a skill that’s effective on one type of enemy. It takes many soldiers to win a war.

The anaerobic (oxygen-free) environment may kill one pathogen, but has no effect on others.

Same with salt. They kill some pathogens, but not others.

Acid is the sleeper weapon. It starts out lazily at pH 6.9. But once it hits pH 3.0 to pH 4.0, it’s a pathogen’s worst nightmare.

Together though, a lack of oxygen, acid, salt, and lactic acid bacteria keep your sauerkraut safe.

Will Homemade Sauerkraut Make Me Sick?

What if I consume a pathogen that survives in my sauerkraut?

Well, the more pathogen cells you consume at one time, the greater your chances of illness. The opposite is true, too. The fewer pathogens you consume at once, the less likely you are to become sick. This is called ‘Pathogen Load’.

We can eat pathogens without getting sick. Stomach acid and other parts of your immune system kill the few that make it to and past your gut into your body.

Usually.

But, when you consume a vast army of many pathogen cells at once, getting sick is likely.

When you properly make fermented cabbage, you’ll never face an army of pathogens. It’s possible (but unlikely) a few pathogen cells will be in there. But they’re hanging on for dear life. Sauerkraut is a rough environment for them.

I don’t intend any of this to scare you.

It’s informing you.

The popularity of fermented foods and their uprising in society sometimes causes “holy grail syndrome”.

Pathogens have excellent defenses. They can take a lot of punishment.

Don’t overthink it though.

If you make sauerkraut at home correctly, the risks are slight.

It’s hard to find cases of sickness from properly made homemade sauerkraut. You’re more likely to become sick from fresh lettuce containing E. coli.

How to Store Sauerkraut at Safe Temperatures

Sauerkraut ferments near room temperature. But, you need to store it in a cool place when it’s finished. Fermented cabbage lasts in the refrigerator for a year or longer. Remember, sauerkraut is not fresh produce. It’s a preserved food. So, it lasts a long time.

Cabbage below the brine won’t spoil at room temperature. Acid makes that possible. But, a few good reasons to move sauerkraut to your home's cold storage are

• locking-in the taste of your sauerkraut.
• preventing pathogens from growing above the brine.

When you leave fermented cabbage at room temperature, it will continue to ferment. And, its flavors will keep changing. The longer, the funkier. Some people enjoy the funk, others don’t.

Further, pathogens sitting outside the brine still multiply.

Pathogens Above the Brine

A high brine level helps protect your sauerkraut. But, cabbage bits float to the top of your brine. This exposes them to air, risking pathogen growth. As you scoop out your fermented cabbage, it contacts those pathogens. As a result, you’ll eat them.

To prevent this, store your homemade sauerkraut at low temperatures to prevent pathogen growth.

Storing Homemade Sauerkraut in the Refrigerator

The best place to store fermented cabbage is in your refrigerator.

It’s possible you put little thought into the temperature of your fridge.

But you should.

Pathogens multiply fast above 4°C (40°F). The warmer, the faster.

They won’t grow deep within your sauerkraut because it’s acidic and oxygen-free. But you expose the sauerkraut's surface to oxygen every time you open that mason jar. That could lead to yeast and mold at warm temperatures.

What temperature should my refrigerator be?

The U.S. Food and Drug Administration recommends refrigerator temperatures of 3°C to 4°C (37°F to 39°F).

Did you notice they recommend a temperature just below the level pathogens multiply freely?

But the ideal temperature range is 1.7°C to 3.3°C (35.06°F to 37.94°F). This completely stops food-bourne pathogens without freezing your food. For example, Clostridium botulinum has a minimum growth temperature of 3.3°C (37.94°F).

Control Your Refrigerator Temperature

Your fridge may display its temperature to you. If it doesn’t, buy a hanging thermometer. You’ll see it every time you open the fridge door.

I’ve heard of people raising the temperature of their refrigerator to save on electricity costs.

Don’t do that.

The money you save isn’t worth the risk of eating contaminated food. Anyone with food poisoning will tell you they’ll gladly do anything to make the stomach cramps go away.

Preserving Texture and Flavor

When you put fermented cabbage in the fridge, it stops fermentation. So, your sauerkraut’s taste won’t change much. But, flavors keep developing slowly. That’s a good thing.

Over time, the texture of your homemade sauerkraut may soften, but it’s still fine to eat.

Low Brine Levels in the Fridge

You might notice your brine level lowers once in the refrigerator. This is because the brine gets re-absorbed into the cabbage. To remedy, push down your sauerkraut to raise the brine level.

Storing Homemade Sauerkraut in the Freezer

Lactic acid bacteria survive freezing temperatures.

But, several rounds of thawing and refreezing puts stress on bacteria.

You can store food safely indefinitely in the freezer when the temperature is at least -18°C (0°F). But, with any frozen food, flavors may degrade after 8 to 12 months. Personally, I’ve stored foods longer than this in the freezer without problems. With other foods, I’ve discovered what it means for something to taste “freezer burnt”. Freezer burning is more of a texture and flavor issue than a safety issue.

Thawing Frozen Sauerkraut

Don’t thaw fermented cabbage using high heat. Instead, thaw it on the countertop or in the refrigerator. Or, you can place your container of kraut in a bowl of cool water. Then, change the water every 20 minutes.

The defrost setting of your microwave is OK to use. It causes microwaves to cycle on and off. But, check your sauerkraut’s temperature while microwaving. Make sure it doesn’t get near 55°C (131°F). Lactic acid bacteria die at this temperature.

What if you don’t know how to use your microwave’s defrost setting?

Instead, turn your microwave on and off manually.

Microwaves heat food near the outer edges of your container. That’s because microwaves can only go so far into food. Stop your microwave occasionally and stir the sauerkraut. This will mix the warm kraut on the outer edges into the cold center.

Storing Sauerkraut in a Basement, Cellar, or Cool Room

Historically, storing sauerkraut at home in a basement or cellar was (and still is) common. In fact, my father stored fermented cabbage in our basement cold storage room throughout the 1980s and 90s. I ate lots of it and didn’t get sick. It’s not wrong to store it this way. But, it’s important to know the risks if you do.

Risks of Storing Sauerkraut at Home in the Basement

Storing fermented cabbage in the basement or cellar has a few risks. If your basement is not 3°C to 4°C (37°F to 39°F), pathogens may grow on your sauerkraut’s surface.

As well, basements are often damp. Dampness causes higher-than-normal numbers of mold spores. These mold spores can land on your fermented cabbage when you open the mason jar.

Leave Sauerkraut in the Basement for Convenience

Let’s say you’ve fermented cabbage in a 45 liter (10-gallon) monster crock in your basement’s cold storage room. It can be difficult carrying that crock up the stairs. It’s even more difficult to shove that giant monster into your refrigerator. So, it makes sense to leave it in the basement.

This may work if your basement temperature is near 12°C to 16°C (54°F to 61°F). Even lower is better. Your sauerkraut will continue to develop flavors when storing it this way.

But, there’s surface mold and yeast risks at these temperatures.

Instead, fill 1 liter (1 quart) glass mason jars with sauerkraut. Then, put them in the refrigerator at 3°C to 4°C (37°F to 39°F).

Conclusion

The next time you make sauerkraut, you’ll be much better equipped to succeed. Let’s take a look at what you’ve learned . . . You understand how salt, acid, a lack of oxygen and lactic acid bacteria work together. The science of fermentation actually makes some sense now! All this time, you knew those internet recipes were missing something. Mold and yeast are no longer problems you deal with. Instead, you prevent them. And, you have a closer relationship with lactic acid bacteria. Now you know what makes them ‘tick’. Are you feeling better about what’s going on in your sauerkraut jar?

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And while you’re here…please do leave a comment. Ask a question. Let us know your experience or opinion. I’d love to hear it!

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