Airlock still active 15 days later, should I worry?

I brewed up my own recipe for a Cascadian Dark Ale. After a scary vigorous first few days when I had a blow off tube collect about 2 cups of slurry, the airlock has not stopped. I'm now at the 15 day mark. The airlock is still at it, one bubble every 20 seconds or so. This is my third brew ever. My other two brews were done by now. I've not measured the SG, as its clear that it is not done fermenting yet. I used beersmith to create my recipe. It suggested that either I make a 3 liter starter, or pitch 3 vials. I chose to pitch 3 because I did not have the time to make a starter.

Here is the recipe:

2lb Crystal 60 - steep 30 minutes
8oz Black Patent Malt - steep 10 minutes
8oz Chocolate Malt - steep 10 minutes
10 lbs Pale LME
1oz Chinook
1oz Columbus
1oz Cascade (substituted falconers flight because LHBS was out)
3 vials White Labs #WLP001
2oz Cascade (dry hopped) (substituted falconers flight)

Measured OG 1.068
Estimated IBUs 62.0
Estimated SRM 40.4
Estimated ABV 7.0%

The taste I took when I dry hopped was wonderful. The smells coming out of the airlock are amazing. I expect that this will be my best brew yet. But.... do I have any reason to be concerned that fermentation is still so active for this long? I have patience, but I have worry too.

This is, however, the highest ABV brew I've tried so far. Is that the reason for the lengthy fermentation?

No worry.

Yeast can't read a calendar. Each fermentation is different. I have had them reach FG in a couple of days and had them show active signs of fermentation for weeks. It will be done when it is done.

I would not worry. You did the correct thing but taking a hydro reading. Just pretend like the airlock is non existent. If the gravity is falling then the yeast are still cleaning up and eating the remaining sugars. Maybe you could warm the fermenter just a little bit to encourage them to finish. Oh yeah, and next time plan ahead and save a ton of $$$ and make a starter!

My Imperial Stout is at 2 weeks, and its still bubbling. Its all good.

Definitely check the gravity. For future practice, wait to dry hop until fermentation is complete...

Nope and it's more than likely done. You're probably getting off gassing form the dissolved CO2 in the liquid changes in pressure and temperature can affect the solubility of CO2 and it comes on out... The best way to tell if it's done is to take a look at your FG using your handy dandy hydrometer. AT 15 days out, I bet you're in the 1.0-teens right now and done or pretty close to it.

BradleyBrew said:

You did the correct thing but taking a hydro reading.

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I have not yet taken a hydro reading. Airlock clearly shows that the yeast are still busy. I don't want to needlessly open the bucket.

When did you add the hops sounds like a good recipe I'd love to brew it

abrew2u said:

When did you add the hops sounds like a good recipe I'd love to brew it

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I added the hops after a week.

JohnRudolfLewis said:

I have not yet taken a hydro reading. Airlock clearly shows that the yeast are still busy. I don't want to needlessly open the bucket.

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why are you afraid to open the bucket. just don't go mucking around in the beer, take a hydro reading when you want. Sanitize anything going in the beer and its all safe. your being too paranoid.

When and how many hops were added to the boil sorry for the confusion.

JohnRudolfLewis said:

I have not yet taken a hydro reading. Airlock clearly shows that the yeast are still busy. I don't want to needlessly open the bucket.

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Um.... no. The airlock shows off gassing. The hydrometer essentially demonstrates what the concentration of dissolved unfermentable and fermentable sugars are in solution. If you are interested in knowing whether or not you're done or still fermenting taking multiple hydrometer readings is the only way to know for sure.

Presence or lack of bubbling in airlock cannot be used to determine whether or not fermentation is occurring. Check the gravity...

JohnRudolfLewis said:

I have not yet taken a hydro reading. Airlock clearly shows that the yeast are still busy. I don't want to needlessly open the bucket.

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woopsie! sorry!