This is a question that I get from time to time, from vegans or people with a milk allergy or lactose intolerance.It is possible to make non-dairy yogurt. But... there's always a but.
Dairy free yogurt is actually a contradiction. You can force the cultures to feed of alternate energy sources for a while but you can’t keep it for many generations, the micro organisms will eventually die off, so you need new starter every time you make it and it’s benefits are not comparable to yogurt as the variety of microorganisms that can thrive on non dairy alternatives is different subset.Yogurt forms when bacteria ferment the sugar lactose (C12H22O11) into lactic acid (C3H6O3). The lactic acid makes the milk more acidic (lowers the pH), causing the proteins in milk to coagulate.
It's basically the equivalent of putting humans on a hamburger diet, they will do ok the first few days but after a week or so their health will deteriorate.These bacteria will then survive by trying to ferment other sugars but this depletes their reserves as these alternate fermentations are less optimal. Also the coagulation process is not always the same on soy or coconut milk so often you need to add additives to help thicken the yogurt.
Does this mean you can't do it?
No of course not, you will find many recipes online which are certainly helpful if you dairy based yogurt is not an option for you.In the end you always end up using new starters. There are starters for sale that are engineered to do well on non dairy “milk” alternatives but those are certainly not heirloom cultures. But even then in order to keep on using them you still need to buy new starter.
Our starters are heirloom starters which means once you use them you can keep using them until you die so to speak in fact they will be able to survive us. I wouldn’t recommend these for making non-dairy yogurts although I have tried it and it works on coconut milk for example. But in that case I started with a spoon of fresh starter grown on real milk.If you are lactose intolerant know that yogurt fermentation +/- halves the lactose content in the milk depending on how long you let it ferment and whether or not you drain the whey. So a teaspoon of starter will most likely not cause any trouble for lactose intolerant people if used to start up your non dairy yogurt.
Of course if you are allergic that’s a whole different story. If you want to save yourself some money, buy probiotic capsules that are guaranteed dairy free. Just add a capsule to your coconut or soy milk and you are good to go. If using coconut milk use thick creamy coconut milk so you won't have to add any additional thickener.Also note that you will most likely have to use a yogurt maker as the strains in those probiotic capsules are most likely thermophilic (=require some heat to culture) unlike our cultures that culture at room temperature.