I have brewed a few batches before using kits from MidWest Supplies. So far, no problems.
For this batch, I wanted to create my own recipe for a Blueberry Ale. Here is a gist of the ingredients:
5lb Wheat DME
1 oz hops (I forget which kind)
1 packet American Yeast (I think it was 1010)
1lb frozen blueberries
So, on the brew day, we followed this process:
1) bring water to boil
2) add fermentables (not blueberries)
3) add 1/2oz of hops
4) boil for 45 min
5) add 1/2oz hops
6) boil for 10 min
7) add blueberries
8) boil for 5 minutes
9) cool and move to fermenter
So, that's what we have done so far. We usually have an air lock and that works fine. However, with this batch, we had a lot of blowoff and had to jerry-rig a blowoff tube. I think we have avoided any contamination issue, but it got me wondering... why did we need a blowoff tube THIS time, when we never did before?
I think there are 2 likely culprits:
1) the frozen blueberries caused it to foam up
2) this was the first time we used ONLY extract in brewing, maybe that causes more foam?