Lots of people ask me how to make probiotic yogurt. Here, we'll look at the problems associated with making your own.
I'm a great fan of homemade yogurt and make my own using the EasiYo system. It's chock full of lactic acid bacteria including a probiotic strain L acidophilus NCFM.
However, I'm not a big fan of trying to make your own probiotic yogurt. Here's why.
To make yogurt you need the two starters Streptococcus thermophilus and Lactobacillus delbrueckii subsp bulgaricus. These two have been used for hundreds of years because they have a synergism between them where each feeds the other and they produce a rapid and efficient acidification of the milk and multiplication of the two cultures1. Not all strains of these two bacteria can do this but you will find the right strains in any cup of live yogurt.
But as soon as you start adding probiotic bacteria, the very qualities that make them beneficial to your health, make them bad companions for the yogurt starters.
Probiotic bacteria produce things like bacteriocins which have an antibiotic effect - this means they start to kill the yogurt starter bacteria1. Add in the hydrogen peroxide, benzoic acid (produced from the minor milk constituent hippuric acid), biogenic amines (formed by decarboxylation of amino acids), and lactic acid and those starter bacteria take a real beating.
So whilst bacteriocins are good for your health in that they help stop bad bacteria from multiplying, you don't want them doing that before your yogurt has had a chance to ferment.
Commercial makers of yogurt get round these problems by making the yogurt using the usual starters and then cooling the yogurt to slow down the process and only then adding the probiotic. Even so, if the yogurt is stored for too long the probiotics are slowly being killed off by the yogurt starters.
It's a bit of a Catch 22. Any probiotic you add is likely to adversely effect the starter culture.
At the same time, you have to have the two starters to make yogurt but they're likely to kill off any other bacteria you add.
And exactly what happens varies depending on the strain of these different cultures.
Unless you have a laborartory at your fingertips you have no idea what it happening within that cup of yogurt.
So to make probiotic yogurt you should make the yogurt normally and then add the contents of a probiotic supplement just before eating it. That is the only safe way to do it being sure that you are actually getting the probiotic that you wanted in your yogurt.
But I know that isn't what most people want - they want to feel that they are growing the probiotics. I see lots of suggestions on how to make probiotic yogurt on forums etc but unless you're have laboratory facilities you actually have no idea what you're growing. Just because you empty a capsule of your favorite supplement into your yogurt does NOT mean that it is enjoying the experience!
And it doesn't mean that it is increasing in number. It might be quite the opposite with the total numbers of good bacteria being substantially lower than in a regular yogurt.
You just don't know.
And that is the whole problem with trying to grow your own probiotics in yogurt.
My answer is stop fretting about growing your own probiotics - it's tricky stuff and best left to the scientists. Concentrate on either making or buying a yogurt with live and active bacteria in it - don't worry about which specific lactic acid bacteria they are, they're doing you good - and take a probiotic supplement seperately.
Metchnikoff, the "father" of the whole probiotic movement made ordinary yogurt. If it was good enough for him - it's good enough for me!
1. Heller KJ. Probiotic bacteria in fermented foods: product characteristics and starter organisms. Am J Clin Nutr. 2001 Feb;73(2 Suppl):374S-379S.
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