How to Make Yogurt at Home: Milk, Temperature, Time and Troubleshooting
- NPSelection
- Nov 8, 2017
- 15 min read
Updated: 1 day ago
Making yogurt at home can be very simple, but it is not always instant. Milk may appear to be a basic ingredient, yet small differences in its protein content, processing and freshness can change the final result. The starter culture, temperature, fermentation time and cleanliness of the equipment also affect how quickly the yogurt sets and what its final texture will be.
Once these basic elements are understood, the process becomes much more predictable.
In this guide, we will explain how to make yogurt at home using dairy milk and a yogurt starter culture. We will also look at milk preparation, fermentation temperature, timing, reculturing and the most common reasons why homemade yogurt sometimes remains thin, separates or becomes too sour.
For a simple explanation of what happens inside the milk during fermentation, read: How fermentation changes milk
How do you make yogurt at home?
Heat (or boil) one litre of dairy milk to approximately 82–90°C, then cool it to lukewarm. Add the starter, mix thoroughly and incubate without disturbing the container.
Many traditional yogurt cultures ferment at approximately 40–45°C. However, specialist cultures may require a lower temperature, so always follow the instructions supplied with the starter.
A first batch made from a freeze-dried NPSelection starter commonly requires approximately 12–16 hours when yogurtmaker is used. A later batch made with a few spoonfuls of finished yogurt usually ferments more quickly or 3 to 6 hours.
When the yogurt has set, refrigerate it promptly to slow the fermentation.
What is yogurt?
Yogurt is milk that has been fermented by selected lactic acid bacteria.
Traditional yogurt is made using two defining bacterial species:
Streptococcus thermophilus
Lactobacillus delbrueckii subsp. bulgaricus
These bacteria work together during fermentation. They use some of the lactose, which is the natural sugar in milk, and produce lactic acid.
As the acidity increases, the structure of the milk proteins changes. The milk becomes thicker, develops its familiar sour flavour and turns into yogurt.
Other bacterial species, including Lactobacillus acidophilus, bifidobacteria, Lactobacillus rhamnosus, Lactobacillus gasseri, Lactobacillus salivarius and Limosilactobacillus reuteri, may be included in different cultured-milk preparations. These combinations can produce different fermentation speeds, flavours and textures.
Yogurt starter culture versus ready-made yogurt
You can start a batch of homemade yogurt in two main ways:
With a small quantity of plain ready-made yogurt containing active cultures
Both methods can work, but they are not identical.
Using a freeze-dried starter culture
A freeze-dried starter contains selected bacteria in a dry, inactive form. Once it is mixed with suitable milk and kept at the correct temperature, the bacteria become active and begin fermenting the milk.
The first batch normally takes longer because the freeze-dried bacteria must first absorb moisture and adapt to the milk before fermentation becomes visibly active.
A starter culture also allows you to choose the type of yogurt you want to make. For example, you can choose a traditional Bulgarian yogurt, a milder Bifido yogurt or a preparation containing Acidophilus and other selected species.
Choose a yogurt starter culture
NPSelection offers freeze-dried starter cultures for Bulgarian, Bifido, Acidophilus, Balkan-style and other types of homemade yogurt.
Each culture has its own bacterial composition and may produce a slightly different flavour, texture and fermentation pattern.
Using ready-made yogurt as a starter
Plain ready-made yogurt can also be used to start a new batch, provided that it contains active cultures.
Choose a plain yogurt without:
Fruit
Flavouring
Sweeteners
Preservatives
Large amounts of starch or stabilisers
The exact cultures and their activity may vary between commercial products. For this reason, the result can be less predictable than starting with a newly opened freeze-dried culture.
Ready yogurt is usually more active than a dry starter because its bacteria are already hydrated. A recultured batch may therefore be ready within approximately three to six hours, depending on the temperature, milk and culture.
Do not assume that every commercial product labelled as yogurt will successfully reculture. Some products may have low culture activity, may have been stored for a long time or may contain ingredients that interfere with the process.
Which milk is best for making yogurt?
The milk provides both the food required by the bacteria and the proteins that form the yogurt’s structure.
For beginners, pasteurised whole cow’s milk is normally the easiest option. It generally produces a fuller flavour and creamier texture than semi-skimmed or skimmed milk.
However, several types of dairy milk can be used.
Whole cow’s milk
Whole cow’s milk is usually the most reliable choice for a thick, creamy homemade yogurt.
Look for plain milk without added flavouring or unnecessary ingredients.
Semi-skimmed milk
Semi-skimmed milk can ferment successfully, but the finished yogurt will often be softer and less creamy.
This is not necessarily a fermentation failure. It may simply reflect the lower fat content or the particular protein structure of the milk.
Skimmed milk
Skimmed milk can also be fermented, although the result is more likely to be thin.
Some people add skimmed-milk powder to increase the protein content. Another option is to strain the finished yogurt after refrigeration.
UHT milk
UHT milk can be used for homemade yogurt. Because it has already received a high-temperature treatment, some people use it without reheating.
However, heating it again can still improve consistency and reduce variation between batches. Follow the instructions supplied with your chosen starter.
Goat’s milk
Goat’s milk can make yogurt, but it often produces a softer texture than cow’s milk because its protein structure is different.
The finished yogurt may be creamy rather than firmly set.
Sheep’s milk
Sheep’s milk naturally contains more solids and often creates a rich, thick yogurt.
It may ferment slightly differently from cow’s milk, so monitor the batch rather than relying only on a fixed number of hours.
Raw milk
Using unheated raw milk makes the fermentation less predictable and can introduce food-safety concerns. For a more controlled process, use pasteurised milk or heat the raw milk before adding the starter.
Read more here: Can I use raw milk when making yogurt and/or kefir?
Plant-based milk
Plant-based yogurt-style products require a different method. Plant milks do not contain the same proteins and natural sugar as dairy milk, so they may need an added food source, thickener or adapted starter.
Read the separate guide here: How to make yogurt and kefir with plant-based milk
Milk quality can vary considerably between brands and even between different cartons from the same producer.
For a more detailed explanation, read: Milk Quality: The Hidden Foundation of Yogurt and Kefir Fermentation
Why is milk heated/boiled before making yogurt?
Heating/boiling the milk serves more than one purpose.
First, it reduces the number of competing microorganisms that could interfere with the starter culture.
Second, heating/boiling changes the behaviour of the milk proteins. This helps them form a stronger structure when the milk becomes acidic during fermentation.
This is why properly heated milk often produces a firmer yogurt with less whey.
For a reliable home method, heat the milk to approximately 82–90°C. Hold it in this range for around 10–20 minutes if you want a thicker result.
Do not leave the milk unattended. Stir it gently from time to time to prevent it from catching on the bottom of the saucepan.
The longer heating period is mainly intended to improve texture and consistency. The milk does not need to boil violently.
For more information, read: Why milk is heated before making yogurt and kefir
Cooling the milk before adding the starter
After heating/boiling, the milk must be cooled before the starter culture is added.
Adding the culture while the milk is too hot can damage or destroy the bacteria.
The correct temperature depends on the culture.
Traditional thermophilic yogurt cultures, including Bulgarian-style combinations, are usually incubated at approximately 40–45°C.
Some specialist combinations containing additional bacterial species may require a lower temperature, often around 36–39°C.
Nordic and other mesophilic cultures may work at considerably lower temperatures although they perform well at higher temperatures as well.
Touching the outside of the container can provide a rough guide of correct temperature; if it feels lukewarm, then fine.
Temperature is more important than speed
Do not increase the temperature simply because the yogurt appears to be fermenting slowly.
Excessive heat can weaken the starter, create uneven fermentation or cause the milk to separate.
A stable temperature within the range recommended for the culture is better than a hotter temperature.
What equipment do you need?
You do not need a complicated kitchen setup.
For a basic batch, you will need:
A saucepan
A clean spoon or whisk
A food thermometer (optional)
A clean glass, ceramic or food-safe container
A lid
Milk
A suitable yogurt starter
Yogurt maker or other method that can maintain a stable temperature for long
You can maintain the incubation temperature with:
An electric yogurt maker
A multicooker
An Instant Pot with a yogurt setting
A sous-vide device
An insulated container
Another temperature-controlled fermentation device
The important function of the equipment is not its brand. It must maintain the correct temperature steadily without overheating the milk.
For help choosing a machine, read: Choosing the Right Yoghurt Maker: A Beginner’s Guide
For multi-cooker instructions, read: How to make yogurt at home with an Instant Pot
How to make yogurt at home step by step
The following method is suitable for approximately one litre of dairy milk. The instructions on your starter pack should take priority where they differ.
Ingredients
One litre of dairy milk
One sachet of yogurt starter intended for one litre of milk
Alternatively, for reculturing:
One to three tablespoons of plain finished yogurt
One litre of prepared milk
Step 1: Clean the equipment
Wash the saucepan, spoon and fermentation container thoroughly.
Rinse them well so that no washing-up liquid remains.
You can also pour over the container and utensils with hot water. Allow them to drain without touching the inside surfaces unnecessarily.
Good hygiene is particularly important when you plan to reculture the yogurt for later batches.
Step 2: Heat/boil the milk
Pour one litre of milk into a saucepan.
Heat it slowly to approximately 82–90°C. Stir gently to prevent the milk from catching.
For a thicker result, keep the milk hot for approximately 10–20 minutes.
Step 3: Cool the milk
Remove the saucepan from the heat.
Allow the milk to cool to the temperature recommended for your starter culture.
For many traditional yogurt starters, this will be approximately 40–45°C. Do not assume this range is correct for every culture.
Step 4: Add the starter
Once the milk reaches the correct temperature, add the starter culture.
Mix gently but thoroughly so that the starter is evenly distributed.
Avoid creating excessive foam.
When using an NPSelection freeze-dried starter, one sachet is normally intended for approximately one litre of milk. Follow the quantity shown on the product packaging.
Step 5: Allow the starter to hydrate
After mixing, allow the milk and starter to stand for approximately 10–20 minutes.
Stir gently once more before placing the container in the yogurt maker or incubation device.
This short period gives the freeze-dried culture time to absorb moisture.
Step 6: Incubate at a stable temperature
Place the container in the yogurt maker or chosen incubation device.
Do not shake, stir or repeatedly move the container while the yogurt is setting.
For many NPSelection freeze-dried yogurt starters, the first batch commonly requires approximately 12–16 hours.
However, the actual time can be shorter or longer depending on:
The bacterial combination
The milk
The incubation temperature
The amount of starter
The yogurt maker
Step 7: Check whether the yogurt has set
The yogurt is generally ready when it has visibly thickened and formed a coherent structure.
Some cultures form a firm set. Others remain soft, creamy or slightly drinkable.
Tilt the container very gently. The surface should move as one mass or show clear thickening rather than moving like ordinary milk.
Do not stir the yogurt simply to check it. Stirring breaks the developing structure.
If you measure acidity, yogurt commonly finishes near pH 4.5–4.6. The exact stopping point depends on the desired taste and texture.
Read more here: Why pH can be more useful than fermentation time
Step 8: Refrigerate promptly
Once the yogurt has set, move it to the refrigerator.
Cooling slows the activity of the bacteria and helps the yogurt’s structure become firmer.
Leave it undisturbed in the refrigerator for at least several hours before stirring or serving. Overnight refrigeration often produces the best texture.
Step 9: Add flavours after fermentation
Add fruit, honey, vanilla, jam or other flavourings after the yogurt has fermented and cooled.
Adding them before fermentation can introduce additional microorganisms or ingredients that interfere with the starter.
If you intend to reculture, remove a clean portion for the next batch before adding any flavouring.
Ready to make your first batch?
Explore NPSelection starter cultures for traditional Bulgarian yogurt, Bifido yogurt, Acidophilus yogurt and other cultured-milk styles.
One sachet is normally used with approximately one litre of milk, and the finished yogurt can be used to start later batches.
How long does yogurt take to ferment?
There is no single fermentation time suitable for every yogurt.
A first batch made with a freeze-dried starter often takes longer than a batch made with ready yogurt.
As a general guide:
First batch from a freeze-dried NPSelection starter: commonly around 12–16 hours with yogurt maker
Later batch made from finished yogurt: commonly around 3–6 hours with yogurt maker
Lower-temperature specialist cultures: potentially longer
Excessive temperature: may cause separation rather than a faster, better result
Treat these times as observation points, not automatic finishing times.
Look at the yogurt itself. When it has set, it should be refrigerated.
Leaving an already-set yogurt in the machine for many additional hours will normally make it more acidic and can eventually cause it to separate.
What should homemade yogurt taste and look like?
The exact result depends on the milk used and incubation time.
Homemade yogurt may be:
Firm and sliceable
Thick and creamy
Soft-set
Smooth and spoonable
Slightly stringy
Mild
Sharply sour
Rich and buttery
Light and refreshing
A traditional Bulgarian yogurt is normally pleasantly sour and may form a firm, clean set.
A Bifido yogurt may be milder and creamier.
A culture containing different bacterial species may produce another texture entirely.
Texture alone does not show that one starter is better than another. The purpose is to make the style of fermented milk associated with the selected culture.
For more information about Bulgarian yogurt, read: What Is Bulgarian Yogurt and How Do You Make It at Home?
To explore the corresponding cultures: Bulgarian yogurt starter cultures
How to reculture homemade yogurt
Reculturing means using a portion of finished yogurt as the starter for a new batch.
Before eating or flavouring the first batch, place one to three tablespoons of freshly prepared yogurt into a clean, covered container.
Keep this portion refrigerated.
To make the next batch:
Prepare and heat one litre of fresh milk.
Cool it to lukewarm.
Add one to three tablespoons of the previous yogurt.
Mix thoroughly.
Incubate at the correct temperature.
Begin checking after approximately three hours.
Refrigerate as soon as the new batch has set.
A recultured batch generally ferments more quickly because the bacteria are already active and hydrated.
The number of successful recultivations depends on:
Cleanliness
Milk quality
Temperature
Cross-contamination
The activity of the previous batch
Reculturing should not continue automatically when the result becomes weak or unusual.
Start again with a fresh sachet when:
Fermentation becomes consistently slow
The yogurt no longer sets properly
The smell changes
The flavour becomes unpleasant
The culture has been contaminated
The yogurt develops unusual colours
Read the complete reculturing guide here: How to reculture yogurt and kefir
Why did my homemade yogurt not set?
A yogurt that remains completely liquid has usually experienced a problem with the milk, temperature or time.
The milk was too hot when the starter was added
High temperatures can damage the bacteria.
Always cool the heated milk before adding the culture.
The incubation temperature was too low
If a thermophilic starter is kept far below its preferred range, fermentation may become very slow.
Check the actual temperature inside the machine with a thermometer.
The incubation temperature was too high
Excessive heat can also weaken the bacteria.
A machine that feels warm on the outside may be considerably hotter inside.
The milk contained interfering ingredients
Flavoured milk, preserved plant milk or milk mixed with other ingredients may not ferment normally.
Use plain milk for the first attempt.
The batch needed more time
A freeze-dried starter may show little visible change during the early stages.
Keep the temperature stable and continue
Do not compensate by increasing the heat.
Why is my homemade yogurt thin?
Thin yogurt does not always mean failed fermentation.
Possible causes include:
Low-protein milk
Semi-skimmed or skimmed milk
Milk that was not heated sufficiently
A naturally soft-setting culture
Movement during incubation
A low incubation temperature
Insufficient fermentation time
For a thicker result:
Try whole milk
Heat or boil the milk to 82–90°C
Hold it hot for 10–20 minutes
Avoid moving the container during fermentation
Chill the yogurt fully before stirring
Strain the cold yogurt if you want a Greek-style texture
Read more here: How to make thicker homemade yogurt
Why is there whey on top of the yogurt?
A small amount of clear or yellowish whey is normal.
More extensive separation may be caused by:
Fermenting for too long
Excessive temperature
Moving the container while the structure is forming
A weak milk-protein structure
Repeated reculturing
Stirring before refrigeration
If the yogurt smells and tastes normal, a small amount of whey can usually be stirred back in after chilling or poured off.
Strong separation into solid curds and a large amount of whey commonly means that the yogurt was over-incubated.
Why is my yogurt lumpy, stringy or ropy?
Some cultures naturally produce a slightly viscous or stringy texture. This is particularly common in certain traditional cultured milks.
However, an unexpectedly lumpy, slimy or inconsistent texture can also result from:
Slow fermentation
Unstable temperature
Weak starter activity
Contamination
Uneven mixing
Repeated reculturing
Unsuitable milk
If the smell, colour or flavour is unusual, do not consume the batch.
Read the detailed troubleshooting guide: How to fix lumpy, ropy, sloppy or viscous yogurt
Why is my yogurt too sour?
Yogurt becomes more acidic as fermentation continues.
It may become too sour when:
It is incubated for too long
The temperature is too high
It is left warm after it has set
A highly active recultured starter is treated like a first-batch starter
Too much ready yogurt is used to start the next batch
Refrigerate the yogurt once it has set.
For the next batch, begin checking it earlier. Do not automatically use the same fermentation time for the first and subsequent batches.
Why does my yogurt smell or look unusual?
Normal yogurt should smell clean, fresh and pleasantly acidic.
Discard the batch if you see:
Pink, green, blue, black or orange growth
Visible mould
An unpleasant rotten smell
An unexpected alcoholic or strongly yeasty smell
Swelling or excessive gas in a yogurt that should not produce gas
Signs that the container was contaminated
Do not taste a visibly spoiled batch to decide whether it is safe.
When in doubt, start again
Fermentation should produce a clean acidic smell and a result appropriate for the chosen culture.
If the colour, smell or appearance is clearly abnormal, discard the batch, clean the equipment thoroughly and begin again with fresh milk and a fresh starter.
How should homemade yogurt be stored?
Refrigerate homemade yogurt promptly after it has set.
Keep it in a clean, covered container at approximately 5°C or below.
For the best quality, consume it while it is fresh, normally within approximately five to seven days. Storage time can vary according to hygiene, milk, acidity and the ingredients added after fermentation.
Use a clean spoon each time. Avoid eating directly from the main container if you intend to keep it for several days or use it for reculturing.
Store the portion intended for reculturing separately from the yogurt intended for eating.
Frequently asked questions
Can I make yogurt without a yogurt maker?
Yes. Any method that maintains the correct temperature steadily can work.
You can use an insulated container, multicooker, sous-vide bath or warm oven. Measure the temperature rather than assuming the device is suitable.
Can I make yogurt in an Instant Pot?
Yes, provided that the model has an appropriate yogurt function or another setting capable of holding the required temperature.
Can I use cold milk?
A cold-start method can work with some UHT or ultra-filtered milks and particular starters.
However, heating and cooling the milk normally produces more consistent results and a stronger texture. Follow the instructions for your starter and equipment.
Can I use store-bought yogurt as a starter?
Yes, if it is plain and contains active cultures.
The result may vary because the bacterial composition and activity differ between products.
Can I use a probiotic capsule instead of a yogurt starter?
Not every probiotic supplement is suitable for fermenting milk.
A supplement may contain bacteria that do not set milk, may lack important yogurt bacteria or may have been designed for direct consumption rather than food preparation.
For predictable yogurt, use a product intended as a starter culture.
Can I make Greek-style yogurt?
Yes. First, prepare ordinary yogurt and refrigerate it completely.
Place the cold yogurt in a clean cheesecloth or fine straining bag and allow some of the whey to drain away in the refrigerator.
The longer it drains, the thicker it becomes.
Can I add cream?
Yes. Adding some cream to whole milk can make the final yogurt richer.
Do not replace all the milk with cream unless you are following a cultured-cream recipe.
Can I add sugar before fermentation?
It is usually better to make the first batch plain.
Sugar, fruit, syrups and flavourings may contain preservatives or additional microorganisms. Add them after the yogurt has fermented and cooled.
Why does the first batch take longer?
The bacteria in a freeze-dried culture must absorb moisture, become active and adapt to the milk.
In a later batch, the bacteria in the ready yogurt are already hydrated and active, so fermentation usually begins more quickly.
Can I ferment yogurt for 24 or 36 hours?
Longer does not automatically mean better.
Once yogurt has set, continued warm incubation usually makes it more acidic and increases the risk of whey separation.
Use the condition of the yogurt, the correct temperature and, where available, pH rather than following an arbitrary long fermentation time.
Is kefir the same as yogurt?
No.
Traditional yogurt is fermented by its defining bacterial cultures. Kefir contains a mixed culture of bacteria and yeasts.
Read the full kefir guide: What Is Kefir? How to Make Milk Kefir at Home
Start making yogurt at home
The most reliable homemade yogurt begins with four things:
Suitable milk
A starter culture
The correct temperature
Enough time for the culture to work
NPSelection offers starter cultures for several styles of homemade yogurt, from traditional Bulgarian yogurt to mild Bifido and Acidophilus combinations.
You can also ask questions and share your results with other home fermenters
Related guides
References and further reading
Codex Alimentarius. Standard for Fermented Milks, CXS 243-2003.
Utah State University Extension. Tips to Safely Ferment at Home.
This guide provides general food-preparation information. Always follow the instructions supplied with your particular starter culture and use appropriate food-hygiene practices.
Comments