Milk Kefir FAQ | Fermentation

How Long Should I Ferment Milk Kefir?

Milk kefir typically takes 24 to 48 hours to ferment, depending on temperature and grain-to-milk ratio. It is possible for milk kefir to fully ferment in as short as 12 hours, or to ferment for more than 2 days, but we recommend avoiding both these cases for the reasons we will explain below.

If Your Milk Kefir is Fermenting Too Fast (Under 24 Hours)

If your milk kefir is fully fermenting in under 24 hours, you will need to strain quite often, and the texture of the milk kefir will normally be lumpy and runny. Easy fixes are to:

• Double the volume of milk, fermenting for 24 hours instead.
• Discarding some of the kefir grains.
• Placing the jar in a cooler area can also slow down fermentation.

If Your Milk Kefir is Fermenting Too Slowly (Longer Than 48 Hours)

If your milk kefir is taking longer than 48 hours to ferment, there is the risk of bad microbes colonising the milk before the kefir grains can. To fix this, you can:

• Decrease the volume of milk added to each batch.
• Place the jar in a warmer area, especially if the temperature is less than 18°C (65°F).

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What Temperature is Best for Fermenting Milk Kefir?

The optimum temperature for fermenting milk kefir is around 23°C (75°F) – about room temperature. Kefir grains thrive between 18 - 28°C (65 - 85°F), usually completing fermentation in 24–48 hours. Temperatures above this range increases yeast dominance and stresses the grains, slowing down growth and giving them a mushy texture.

Temperatures Below 18°C (65°F)

• Temperatures below this range generally won't kill the kefir grains, but the milk can fail to ferment in 24 to 48 hours.
• Harmful microbes have the chance to grow before the pH drops to a level that kills or inhibits their growth.

Temperatures Above 28°C (85°F)

• Temperatures above this range can damage the kefir grains, giving them a mushy texture, and slowing down or inhibiting growth.
• Higher temperatures also favour the growth of yeast over bacteria, resulting in a yeasty-tasting milk kefir.
• The texture of the milk kefir produced will often be quite thin and lumpy.

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How Do I Know When My Kefir Is Ready?

That depends on when your milk kefir starts to display signs of fermentation and how fermented you want your milk kefir to be. Initial signs of fermentation include: A change in texture, smell, and taste.

You want to see these signs before the 24 hour mark, as it's important for the kefir grains to begin fermenting and quickly drop the pH of the milk, inhibiting the growth of bad bacteria and mould. If you don't see these signs within 24 hours, you should discard the milk kefir to be safe. However, knowing when your milk kefir is ready, versus when it tastes its best to you, are two different things. You can learn more by reading the section below.

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Can I Shorten or Extend Fermentation Time for Taste Preference?

To personalise the taste of your milk kefir in terms of fizziness, acidity, sourness, and sweetness, keep an eye on how far along the fermentation is. This depends on various factors, such as your milk-to-kefir-grain ratio, the external temperature, and the length of the fermentation.

Below are the different levels of fermentation; just keep in mind that these are a general rule of thumb, and that the specific qualities of your milk kefir can vary slightly due to various factors. For example, a slow fermentation at a very low temperature can result in a thick, mild-tasting milk kefir, and kefir grains from different sources can produce slightly different milk kefirs under the same conditions.

Mildly Fermented Milk Kefir

• A slightly sweet, mildly sour smell and taste.
• Little or no effervescence.
• A runny texture.

Moderately Fermented Milk Kefir

• A moderately sour smell and taste, with little sweetness.
  Some effervescence.
• A slight viscosity.

Highly Fermented Milk Kefir

• A strong, tangy smell and taste.
• A high level of effervescence.
• Thick texture.
• Just starting to separate into whey and milk curds.

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What Happens If I Ferment Too Long?

If you ferment for too long (past 48 hours), overfermentation can occur, separating the kefir into whey (yellow liquid) and milk curds (a sticky white mass). This isn't necessarily a bad thing, but the milk kefir will develop an incredibly strong, sour taste.

It'll also have a granular texture due to the small clumps of milk curds. This is unlike a less fermented milk kefir, which will instead have a smooth, creamy texture. As for the health of the kefir grains, the grain's extended contact time with the highly acidic milk kefir can begin to slow down grain growth.

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Can I Ferment Kefir in the Fridge?

Yes, but it takes 5 to 7 days instead of 24 to 48 hours. To ferment in a fridge, follow our milk kefir instructions, but place the milk kefir in the fridge instead of on a kitchen counter. The lower temperature will significantly slow down the activity of the kefir grains, producing milk kefir every 5 to 7 days instead of every 24 to 48 hours. However, there are a few caveats that we will cover below.

Effect on Taste and Texture

First and foremost, the grains take at least one batch to adjust to the low temperatures, so the first fridge-fermented batch will normally have a poor taste and texture. Once the grains have adapted, the milk kefir produced will be:

• More Sour and Thicker: Lower temperatures favour the activity of lactic acid bacteria over yeast, which are responsible for producing lactic acid (sourness) and polysaccharides (thickness).
• Less Fizzy: The decreased yeast activity results in a lower production of CO2, which is responsible for milk kefir's effervescence.

Effect on the Grains

Fermenting at a lower temperature can significantly affect the growth rate, texture, activity, and size of your kefir grains. The temperature of a fridge is generally in the range of 1°C (34°F) – 5°C (41°F). The closer your fridge is to 1°C (34°F), and the longer you continuously ferment milk kefir in a fridge, the more pronounced these effects are:

• Grain Size Decreases: The cold temperatures weaken the polysaccharide matrix, causing big clusters to break apart into small grains.
• Grains Become More Firm in Texture: The grains take on a firmer rubbery texture.
• Grain Growth Decreases: The growth rate of the grains significantly decreases, or even stops entirely.
• Grain Activity Becomes More Sluggish: The activity of the grains can become sluggish, fermenting the milk more slowly. A normal batch or two at room temperature can help 'refresh' the grains.

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Why Does My Kefir Taste Different Each Time?

Milk kefir can be quite variable in taste if conditions aren't constant. One of the main factors that affects taste is temperature and fermentation time.

Temperature

The external temperature can greatly influence the dominance of lactic acid and acetic bacteria over yeasts during the fermentation. Below are the effects:

• A Lower Temperature: Encourages the growth of lactic acid and acetic acid bacteria over yeast.
  • Stronger sour taste.
  • Less carbonation.
  • Less of a yeasty taste.

• A Higher Temperature: Encourages the growth of yeast over lactic acid and acetic acid bacteria.
  • Creates a milk kefir with a slight yeast taste.
  • More carbonation.
  • Less of a sour taste.

Fermentation Level

The fermentation level of kefir depends on factors such as a milk-to-kefir grain ratio, temperature, and fermentation time. Here are the differences between the two:

• Mildly Fermented Milk Kefir: Still contains lots of sugars, and little lactic acid, CO2, or polysaccharides.
  • A slightly sweet, mildly sour smell and taste.
  • Little or no effervescence.
  • A runny texture.
• Highly Fermented Milk Kefir: Contains very few sugars, high in lactic acid, CO2, and polysaccharides.
  • A strong, tangy smell and taste.
  • A high level of effervescence.
  • A thick texture.
  • Just starting to separate into whey and milk curds.

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Why Is My Milk Kefir Separating?

A clear sign that over-fermentation is occurring is when the milk kefir separates into a watery yellow layer of whey and a thick white layer of milk curds. This can result in milk kefir with an undesirably sour taste and lumpy texture. Here are a few easy fixes:

• Discard Some of the Kefir Grains: We recommend using about 1 teaspoon of kefir grains per cup of milk.
• Shorten the Fermentation Time: If you're fermenting for 24 to 48 hours, shorten the fermentation time to 12 or 24 hours.
• Make Larger Batches: Increase the quantity of milk added to the batch so that you can achieve a ratio of ~1 teaspoon of kefir grains to 1 cup of milk.
• Move to a Cooler Location: Milk kefir grains ferment best at a temperature range of 18°C - 28°C (65°F - 85°F). If you're fermenting at the upper end of this range, move your jar to a cooler location.

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How Much Kefir Should I Make at Once?

As much milk kefir as you can drink! The only upper limit is the size of your jar and the number of kefir grains that you have. One teaspoon of kefir grains can ferment around one cup of milk every 24 to 48 hours.

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Should I Stir or Shake the Kefir During Fermentation?

Yes, it is generally a good idea! Here's why:

• Grain Growth: Gives the milk kefir grains access to fresh nutrients, helping them to grow
• Fermentation Speed: Evenly spread the microflora within the milk, giving it access to fresh food and speeding up the fermentation
• Smoother Consistency: Reduces the formation of milk curds, resulting in a more uniform and creamier milk kefir
• Easier Straining: Helps you strain the slightly separated milk kefir if done just before straining.

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Should I Wash My Milk Kefir Jar and How Often?

How often you wash your kefir jar is a personal choice. Most home kefir makers will wash their jar weekly, as a balance between convenience and hygiene. However, there are three main schools of thought which we will summarise below.

Summary

Washing Every Batch

• ✅Maintains a very clean fermentation jar.
• ❌Extra time, increased water usage.
• ❌Potential to damage the kefir grains if residual soap or detergent is left in the jar.

Washing Weekly

• ✅Balance between hygiene and convenience.
• ✅Biofilm/milk kefir residue kickstarts the next fermentation.
• ❌Potential to damage the kefir grains if residual soap or detergent is left in the jar.
• ❌Potential buildup of milk kefir residue.

Never Washing

• ✅Easy and convenient.
• ✅No risk of residual soap or detergent harming the kefir grains.
• ✅Biofilm/milk kefir residue kickstarts the next fermentation.
• ❌Potential buildup of milk kefir residue.
• ❌Higher chance of contamination in the event of a residue buildup.

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Should I Ferment Milk Kefir Without Oxygen (Airtight/With a Lid) or With Oxygen (Covered With a Cloth)?

Either option works. Milk kefir can be fermented both aerobically (with oxygen) or anaerobically (without oxygen). Both options will produce a great milk kefir, but there are a few differences. We recommend the lid method in our milk kefir instructions as it offers a few small advantages and no real disadvantages over using a cloth lid.

Aerobic/Open Lid Fermentations

An open lid fermentation is done by securing a tea towel/cheese cloth to the mouth of the jar with a rubber band. It allows for the exchange of gases – namely oxygen and CO2, throughout the fermentation.

Anaerobic/Closed Lid Fermentations

A closed lid fermentation is done by loosely screwing on the lid of the jar, allowing for gases to escape, but little oxygen to enter. Some people even take this a step further by fully screwing on a lid with a one-way valve.

Comparison

Dust & Insect Protection

• ❌Open Lid: Moderate protection, still a chance for fruit flies to burrow through the cloth.
• ✅Closed Lid: Good protection all around.

Contamination

• ❌Open Lid: Higher chance for contamination from wild microbes, such as kahm yeast.
• ✅Closed Lid: Good protection all around, lower chance of contamination.

Cleaning

• ❌Open Lid: A cheesecloth/tea towel needs to be washed every so often.
• ✅Closed Lid: Can easily be rinsed with water.

Taste Of Milk Kefir Produced

• Open Lid: More yeasty in taste, less sour, and bubbly.
• Closed Lid: More sour in taste, less of a yeast taste and bubbles.

Convenience

• ❌Open Lid: Harder to wash, a correctly fitting rubber band needs to be sourced and replaced when it snaps.
• ✅Closed Lid: Easier to wash, lid comes with jar.

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Why Is My Kefir Too Sour or Too Mild?

That is likely because your milk kefir is not fermented enough, resulting in a milk kefir that is too mild, or that your milk kefir is too fermented, resulting in a sour milk kefir. To fix this, you can do one of the following:

• Play With the Temperature: A higher temperature increases fermentation speed, a lower temperature decreases fermentation speed.
• Change the Fermentation Time: A longer fermentation results in a more sour milk kefir, a shorter fermentation results in a less sour milk kefir.
• Add More or Less Milk: More milk results in a slower fermentation, less milk increases fermentation speed.
• Remove Some of the Grains: Fewer kefir grains will result in a slower fermentation.

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How Can I Make My Milk Kefir Thicker?

In general, milk kefir can vary from just thicker milk to as thick as thickened cream. If you want your milk kefir to be creamy and thick, there are several changes that you can make:

Using Full Cream Milk

• If you're not already using full cream milk, this is one of the easiest change to make for producing thicker kefir.
• The extra fat in the milk contributes to a thicker consistency.

Adding Thickened Cream

• Adding a small amount (or a large amount if you want to treat yourself) of heavy/thickened cream to your milk kefir can dramatically increase the thickness.
• Makes it taste like a dessert.
• Not the healthiest option.

Refrigerating Your Milk Kefir

• Refrigerating your milk kefir for a few hours after straining it from the grains will cause a noticeable increase in thickness.
• This happens as the cold temperatures cause the protein and fat molecules in the milk kefir to solidify and become firmer.

Adding Milk Powder

• Adding ~2 teaspoons of powdered milk per 250 ml of milk will lead to a thicker milk kefir.
  • This is because your milk kefir will now contain extra protein and fat.

Reduce the Temperature

• Milk kefir that's fermented at a cool temperature of around 18°C (65°F) will be thicker than milk kefir fermented at a higher temperature.
  • A slower fermentation coagulates the proteins and fat globules more slowly, helping the mixture to better retain whey and water, resulting in a creamier and more uniform texture.

Increase the Fermentation Time

• If you have been fermenting for 24 hours, increasing the fermentation time to 48 hours can achieve a thicker milk kefir.
  • A fully fermented milk kefir will have a stronger, more sour taste and a thicker texture.

Secondary Fermentation

• Performing a secondary fermentation with or without fruit allows the fermentation to continue.
• This allows for more polysaccharides to be produced and also causes the proteins and fat globules to further cluster and coagulate, thickening the milk kefir.

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What Should Kefir Smell Like During Fermentation?

Milk kefir grains should have a yeasty to sour smell during the fermentation. Other smells, such as vomit, rotten egg, or bitter smell, indicate contamination or that the species of yeast and bacteria within the grains are out of balance.

A lack of any smell, especially after 24 hours, indicates the grains aren't very active. This is common for the first batch or two after receiving new kefir grains.

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Should Kefir Grains Sink or Float?

It is perfectly normal for kefir grains to sink, float, or do both during the fermentation. What matters most is that the kefir grains are fermenting the milk kefir and that the kefir grains are healthy. Below are the main reasons why kefir grains can sink or float.

Why Kefir Grains Can Float

• Trapped CO2: CO2 can become trapped within the kefir grains, causing them to rise.
• Contact With Milk Curds: Sticky milk curds can become attached to the kefir grains, raising them to the surface.
• Active Fermentation: Kefir will float when a fermentation is active.

Why Kefir Grains Can Sink

• Density: Milk kefir grains are denser than milk, causing them to sink.
• No CO2: A lack of CO2, such as with fermentations close to 18°C (65°F), at the start of a fermentation, or at the end of a fermentation.
• Lack of Fermentation: Kefir grains can sink at the start of the fermentation, or once it's mostly over.

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Is It Normal for Kefir to Form a Thick Layer on Top While Fermenting?

Yes, this is very normal. It happens when the pH of the milk kefir becomes low enough to begin to cause separation of the milk into two layers – milk curds, and whey. The milk curds are thick and will trap CO2, causing the curds to rise to the top of the jar. Within the milk curds are also kefir grains, further contributing to the thickness of this layer.

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Do Larger Batches Take Longer to Ferment?

If you are using the same ratio of kefir grains to milk, no, it does not. In fact, we have noticed the opposite – a larger batch of milk kefir can ferment faster. This is because a larger container has less surface area relative to mass, meaning that it can better hold onto the heat, as per the square-cube law.

And because a substantial amount of heat is released by the chemical reactions during the fermentation, a larger batch of milk kefir can become quite warm – this extra heat speeds up the fermentation.

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Why Does My Kefir Get Fizzy While Fermenting?

The fizziness of milk kefir mainly comes from the yeasts within the kefir grains. The yeasts break down the sugars within the milk, producing a substantial amount of CO2, some of which is absorbed by the milk kefir, carbonating it.

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Can I Mix Different Types of Milk in One Fermentation?

You certainly can! In fact, it's a great idea if you're using coconut or other plant-based milks, which lack the essential nutrients that the kefir grains need to survive.

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Does the Season or Climate Affect Fermentation?

Yes, both climate and season can affect fermentation. In winter, when temperatures are lower, your milk kefir will ferment more slowly, whereas in high temperatures will ferment milk kefir faster. A Higher humidity increases the risk of contamination.

Temperature

• Low Temperatures: A slower fermentation over a long time period will result in a thicker milk kefir with more complex flavours and a smooth texture.
• High Temperatures: A fermentation at a higher temperature will result in a fast fermentation, a thinner milk kefir with a gritty texture, and less complex flavours.

Humidity

• Low Humidity: A low humidity will not affect your fermentation.
• High Humidity: A highly humid climate slightly increases the chance for contamination through mould spores, especially if your kefir grains are weak or if you're doing an open lid fermentation (using a cloth and rubber band).