First Extract only batch - blow off issues

Hello, all.

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
3.3lb LME
8oz malto-dextrose
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?

Thanks unionrdr.

I'm not worried about the batch being ruined or anything like that. I'm just wondering if I should plan on this happening again? I may want to invest in a blowoff valve... or maybe not add fruit during the boil

Well, that's not a huge beer...but sometimes fermentation is a little bit aggressive. Probably due to the added sugars from the blueberries, but maybe you had a fresh batch of yeast, too.

For what it's worth, I use a blowoff tube all the time, every time. If I go bigger than 1.080, I use a 1" blowoff tube. After your first blown bucket and the clean up that ensues, you'll find a lot of value in a buck's worth of hose.

With the added sugars, the OG did get up to about 1.080

I don't want to risk blowing a lid, so I will be getting a blowoff valve

edit: the OG was 1.068

I think you want to avoid the boiling of the fruit to avoid releasing the pectins. I know, not related to your original question and it's been ages since I made a fruit beer, so I'm hardly an expert.