Cask went pop - what is maximum pressure?

I've just lost a plastic pin of bitter - it blew out its keystone. I'm slowly recovering from the anguish of such a loss, and starting to figure out what I did wrong...

The OG of the beer was 1044, and FG was 1010, using wlp002 yeast. The gravity was static for a couple of days before I pulled the FV from the fermenting fridge, and it sat around for 4 more days before I racked it into the cask. The cask had been sitting at around 17 degrees for 2 weeks before it went pop.

I primed using 70g of dextrose. Using this calculator...

http://www.brewersfriend.com/beer-priming-calculator/

tells me this should give around 1.7 volumes of CO2.

I used 70g because that is what Kirsten England said here...

http://barclayperkins.blogspot.co.uk/20 ... orter.html

I quote...

"Cask: Standard procedure:

1) let the beer ferment until finished and then give it another day or so. For me right around 5-7 days.
2) Rack the beer to your vessel of choice (firkin, polypin, cornie, whatever).
3) Add primings at ~3.5g/L
4) Add prepared isinglass at 1ml/L
5) ONLY add dry hops at 0.25g/l – 1g/L.
6) Bung it up and roll it around to mix. Condition at 55F or so for 4-5 days and its ready to go. Spile/vent. Tap. Settle. Serve at 55F."

So, where did it all go wrong?

* Should I have waited longer before racking into cask?
* Is 17 degrees too warm (it's a bit above "cellar" temperature)?
* Should I have vented at some point during the 2 weeks?
* Is it over-primed?

I can't find much information about the maximum acceptable pressure inside a cask, but a few places mention 7 psi. That being the case, then 70g of primings is way too much. According to this calculator...

http://www.brewersfriend.com/keg-carbon ... alculator/

1.7 volumes of CO2 at 17 degrees is 12.7psi, nearly twice the 7psi limit!

Get hold of the CAMRA book Cellarmanship and use that . . . I'm not all that sure that taking advice on how to cask beer from an American is actually that bright an idea.

Most breweries would not add priming to their casks and tend to cask a couple of points above final gravity.

17C is a bit warm.

One thing that perhaps you could try next time is to vent the cask using a soft spile after a few days, before using a hard spile to seal the keg until you are ready to drink.

Thanks for the reply Aleman, I hear you regarding taking advice from Americans regarding casking To be fair to Kirsten, he does appear to brew and cask a lot of old English recipes...

I have the Cellarmanship book, and whilst it's great for understanding how to use casks and cellar them, it is a bit more focused on the pub/cellar side and not the brewery side. I've just had a quick flick through, and whilst it has a brief paragraph about primings (mostly echoing what you've said), there is no information on quantity or pressure.

I appreciate many brewers rack into cask before they hit FG, and I decided not to do this as I am typically not aware what my FG is going to be - I don't do a forced ferment test, and since I'm tinkering with other things (water chemistry for one), there is a fair amount of variation. I felt it would be more accurate to ferment out the beer and then weigh out a precise amount of priming sugar.

Also, early racking has the effect as priming - the beer goes into cask with some fermentables for the yeast to nibble either way. Surely it's a question of magnitude. I've read one source claiming that 1 point of gravity equates to 0.6 vols of CO2, and that they rack 2 points before FG. That would infer 1.2 vols in their casks (as opposed to 1.7 in mine). 1.2 vols at 13 degrees is 2.8psi, and even at room temperature (20 degrees) is 7 psi. So that does sound like a much more sensible level (whether that's enough condition for the beer is another story).

Could you fit the shive with a pressure relief valve prior to knocking it into the cask. As well as saving your beer and floor you could also use it to vent the cask and condition the Ale.