ABV Higher than expected

[scuppeteer]

Just a quickie as to what I did wrong... mash too long or too hot?
I have just done a Pale ale and was hoping for around 4.5% ABV, but final turned out to be 5.1%.
Ingredients:
4.5kg Pale
100g Flaked barley
80g flaked maize

Mash Temp was a constant - 69oC
Mash length was 90 mins

In order to get the right ABV do i need to reduce the temp or Mash length or both?
Cheers

[staplefordbill]

That's a good thing! It means you got a higher efficiency than planned - i.e. you got more sugar out of the grain than the recipe anticipated. I've done lots of Graham Wheeler's recipes from Brew Your Own British Real Ale. When I started the brewlength was pretty much spot on, but as I've got better my efficiency's gone up. Now I either get a bit more out by watering down after the boil, or having slightly stronger beer.

If you're consistently getting a higher efficiency you could compensate by reducing the grain bill next time. I'm not sure but I think multiplying the grain bill by expected gravity / original gravity would give you the correct amount. E.g. 4500g pale malt * 4.5 / 5.1 = 3970g. Can someone confirm?

[Hogarth]

69°C is a bit high for a mash temp. But it wouldn't necessarily give you a higher ABV, and neither would a mash time of 90 mins.

What were the original gravity and final gravity? Those are more useful figures than ABV.

[norstar]

Higher evaporation rates will do this as well. If your pre boil gravity was bang on, but you boiled off more wort than you thought, the remaining liquid is going to be more concentrated. Add the yeast and bang, you've got a higher ABV. As Hogarth says however, it's better if you know your gravity figures.

[flytact]

Higher efficiency! As long as your volumes are good then this is good news. Brew a couple more batches to see if you've stepped up in this department. Then you can lower your ingredients to get your desired gravities.

[scuppeteer]

Thanks for the advice guys, might give the next planned brew a miss (was gonna be a mild) and brew my "house ale" to see what happens.
Gravities on the last one:
OG: 1048
FG: 1009

Cheers