Fermentation Fun: DIY Yogurt!


Quest #E3
15 Points

avocado hero

Project Time: 45 Minutes

plus fermentation time

Get Skills!

What you need...

Safety Thoughts

Be careful sterilizing your equipment and pouring out the milk from your large pot; use oven mitts! 

Yogurt Science Time!

Did you know you could make your own yogurt? Did you know that it’s actually pretty easy to do so, and could be an awesome experiment to learn about probiotics, fermentation, and cellular biology??


What are fermentation and probiotics, and why are they important?


Did you know that your body is FULL of bacteria? Bacterial cells outnumber human cells 10 to 1 in the human body! While some of this bacteria can be harmful, we have a symbiotic relationship with much of this bacteria. This means that both we and the bacteria help each other out: our bacteria buddies help fight off the bad bacteria, and we help feed our buddies.

Lots of foods contain some of these bacteria buddies. When we eat these foods, we help restore the collection of good bacteria inside our bodies. Yogurt is one of these foods that makes for a happy microbiome, or happy bacteria inside our digestive systems.


What’s happening in Yogurt:

Yogurt is a form of fermented milk. This means that live bacteria cultures added to the milk eat up sugars and starches, use the energy gained to reproduce themselves and give off lactic acid. This process, called fermentation, thickens the milk and makes it tart.


How Yogurt is Made:

  1. Milk is heated to kill off any bad bacteria.
  2. The milk is cooled slightly to a temperature best suited to good bacteria reproduction.
  3. A “culture,” or collection of bacteria, is added, usually from previously-made yogurt containing live bacteria.  
  4. The bacteria work their fermenting magic over several hours.
  5. Yogurt time!

Now Your Turn!


Grownup Guides

This is serious food science! Guide your kiddos by helping them make sure to minimize germs throughout the process. 

Enhance the experience by…

  • Asking kids to explain to you what is happening with the bacteria in each stage of this process. (The ability to explain a concept demonstrates retention!) 
  • Timing the project so that the yogurt is ready for breakfast the following day. Get crazy with toppings! Fresh or frozen fruit, granola, honey, jam…so many options! 

DIY Yogurt



  • 1 gallon/4 L  whole milk
  • 8-10 tbsp  leftover yogurt


  • Large and deep stainless-steel pot
  • Ice bath
  • 1 medium size funnel
  • 6 1-L or 33.8 fluid ounce (fl.oz) jars
  • 1 thermometer

Yogurt preparation:

  1. Sanitize all equipment and needed surfaces for this project (to make sure there is no bad bacteria that enters the process). **GROWNUPS REQUIRED** Do this by pouring boiling water over your equipment in a bowl or sink VERY CAREFULLY. Make sure to use clean towels and not to touch your yogurt mixture with fingers.
  2. Prepare your ice bath Fill a large bowl, pot, or sink with water and ice. This should be large enough to hold the pot you use to heat your milk.
  3. Pour milk in the deep pot and heat it slowly until it reaches 160-180 F. It is critical to stir it all the time and make sure milk will not overboil. If milk scorches, it will give unpleasant taste to the yogurt.
  4. After it reaches 160-180F, turn it off, cover it with the lid and immediately place it into ice cold water to cool down to the range of 80-110 F.
  5. While you are waiting, place 2-3 tbsp in each jar by allocating fair amount of yogurt in each jar. When the hot milk reaches 80-110 F, pour it through the funnel into your jars.
  6. Seal it with sterilized lids and let ferment in the warm place, preferably at 95-100 F for about 10-12 hrs. You can place it in an oven or on top of the fridge.
  7. Once it is ready, keep it in the fridge and enjoy with your creative choice of mix-ins. Bon appetite!
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