Science Buddies: "Ask an Expert"

Dear Life Technology Scientist,
Hi! My science group is testing fermentation by growing our own yogurt. We are testing different yogurts as starter cultures. So we add milk to sterlized jars containing one tablespoon of yogurt. After about three hours incubating in a cooler, the yogurt is done. What I'm not sure about is that how microorganisms in the yogurt is able to create more yogurt from just adding milk. Thank you so much!
-Kristen

Hello,
This is a very good question. I think to start, you should determine what organism or molecule is specific to yogurt? You may be able to find this out my reading the packaging of the yogurt container. (You should make sure the yogurt you have says Active Cultures-most do). Once you determine what organism/molecule is growing in yogurt you should be able to do an internet search to find out what it needs to grow. For example...does it need sugar, water, any other nutrients? Then you can determine whether milk has these characteristics. If you want to go above and beyond, you could see if there is another substance in addition to milk, that also has those characteristics and see if yogurt cultures will grow in it as well.

Hope this helps get you started!
Katie

Hi Kristen,

Katie has already given you some great information. I just wanted to add a little tidbit. Microorganisms need simple nutrients to survive, and can often grow with just a simple sugar and some essential amino acids. Glucose is one sugar commonly used to grow microbes, but lactose is the sugar present in milk. Many microorganisms can use lactose as their basic source of energy, and this is what the milk provides.

Good luck with your internet search, and please post again (in this same thread) if you have more questions.

Heather