If I'm not mistaken, I think German ale yeast is best fermented in the low 60s. You may have a "hot" fermentation there.
You may need to pull off the airlock and install a blow-off tube, and keep it in the bathtub/shower in case it blows.
I'd try to keep it under 68 degrees, if you can. That will help make a better tasting beer, as well as keep fermentation a bit cooler. Fermentation can actually cause the temperature inside the fermenter to rise as much as 8-10 degrees, so if the room is 70 degrees, it's probably much hotter inside. I use a stick-on thermometer (like for aquariums) to help gauge the temperature of the fermentation.
I'll look for some links on blow off tubes, so you can rig one ASAP.
Edit- maltodextrine doesn't have a thing to do with the fermentation. It's not fermentable. It provides body and mouthfeel.