In France, you can find the soy yoghurt from Sojasun in basically every supermarket, the ones from Sojade in the organic stores. Soy yoghurt is made in the same way as milk-based yoghurt: Take (soy) milk and add some special bacteria (lactobacillales). They will transform your milk into yoghurt. These bacteria need to feed, and they obviously like milk. The original source of those bacteria will usually always come from colonies that have grown on milk-based culture medium. The question is now if the companies producing soy yoghurt are still cultivating their bacteria on milk-based media (or use other animal ingredients), or if they use plant-based culture media. If they use culture media with non-vegan ingredients, their product is, by definition, also not vegan. They can still claim that their product is vegetable, so this problem is not solved by reading the list of ingredients.
The two lovely vegans at a german blog named Laubfresser posted lately that they tried to get an answer from Sojade (which is also sold in german organic stores) if Sojade is really vegan, e.g. if the bacteria are cultured on a plant-based medium or not. Here is the entry (german). The result was that there was no result. Sojade says that this information is confidential. Which is sad, because we have to consider Sojade non-vegan now. As Sojade is french, I thought that this might be a communication problem and wrote an email to Sojade in french.
Using french did not help. I received the exact same "standard" answer from Sojade as the german one, only in french, explaining what bacteria are, how they make soy yoghurt have a nice texture, and that they were good for your digestion. I answered that email, explaining that this was all very nice, but that I wanted to know about what the bacteria eat, similar to what I explained above. At this stage, I also wrote an email to Sojasun. Now I received an answer, and learned at least one useful thing: Sojade and Sojasun belong together. Sojasun is the brand sold in the supermarket, and Sojade in the organic stores. The information about the culture media, however, remains confidential.
I hope that Sojade/Sojasun will think about this again. Luckily, there are companies that have no problem to declare that they grow their bacteria on vegetable media, for example Alpro Soja/Provamel and Le Sojami.
EDIT (September 2012): Finally, finally! They are declaring now that they cultivate their bacteria on vegetable medium. So Sojasun/Sojade is vegan, hurray! Read on here at the website of Tübingen Vegan.
EDIT (September 2012): Finally, finally! They are declaring now that they cultivate their bacteria on vegetable medium. So Sojasun/Sojade is vegan, hurray! Read on here at the website of Tübingen Vegan.