Bubbly Soy Yogurt

[Reece]

I am making my first batch of soy yogurt, and hae just checked it for the first time, 6 hours after innoculating it. It is incredibly bubbly, but seems otherwise OK. Any idea why the jars of yogurt have filled with air bubbles?
I used a small container of soy yogurt with live cultures as starter, and commercial soy milk. To thicken it, I used tapioca starch and agar agar, as per an internet recipe, but used the Wild Fermentation method of a heated cooler to incubate.
Thanks.