Oh, that's a sign of very active grains! Super-fast souring is driven primarily by temperature and your grain-to-milk ratio, not the goat milk's fat content itself. Your room temperature is likely pushing the bacteria into overdrive, especially since the grains are already vigorous.
For a quick fix, I suggest reducing the temperature first. Move your jar to the coolest, darkest place in the kitchen, like a low cupboard. Second, simply shorten the fermentation time. Strain it after 12 to 16 hours instead of a full 24. If those steps don't give you the milder flavor you want, you’ll need to reduce the amount of grains you're using. But a simple adjustment in temperature or time should easily solve your extreme sourness problem!
