I cooked up my first Double IPA recipe over the weekend but have seriously missed the mark with the target gravity. So much so it most definitely won't be a Double.

Target O.G. = 1.085
Actual O.G. = 1.050

Malt bill

The malt bill was as follows:

75%    Maris Otter  
12.5%  Malted flaked oats  
10%    CaraHell  
2.5%   CaraPils

A volume of 30L gave me a rough required extract for 1.085 gravity of 6.66kg. After adjusting the weights for their efficiencies I came out with:

                               Weight      Efficiency    Actual weight
Maris Otter           75%      4.995kg     82.5%         6.055kg
Malted flaked oats    12.5%    0.833kg     70.0%         1.190kg
CaraHell              10%      0.666kg     74.0%         0.900kg
CaraPils              2.5%     0.167kg     71.4%         0.234kg

This gave me a total weight of 8.401kg. My mash and sparge volumes were:

Mash = 26L
Sparge = 16L

Mash

The mash started off a little too hot and so I ended up doing a 150 minute mash. The readings went as so:

T = 0    temp = 72.7ºC
T = 20   temp = 71.6ºC
T = 40   temp = 70.1ºC
T = 60   temp = 68.0ºC
T = 80   temp = 66.5ºC
T = 100  temp = 65.8ºC
T = 120  temp = 65.4ºC
T = 150  temp = 64.9ºC

After transferring the wort to the boiler, where it sat on at a low setting for a couple of minutes while I added the sparge water to the mash tun, I had a wort temperature of 68.4ºC and a gravity reading of 1.034. Adjusted for temperature using brewers friend it came out with a reading of 1.051. I was a bit despondent at seeing this.

My sparge after finishing had a reading of 1.017 and a temperature of 73.1ºC. Brewers friend only goes to 71ºC but it gives a rough gravity of 1.035.

There were 400g of hops in the boil/flame out. After boiling and cooling the wort I topped it up with about 3.5L of the leftover sparge water and a further 2.5L of water to top it up to 30L (I also used some of that sparge water to top up the boil). My end gravity was 1.050.

Brewhouse efficiency
Writing this out I realise I did not adjust my recipe for brewhouse efficiency. However, assuming I did nothing wrong, that gives me an appalling efficiency of 58.8%. That is so bad I think there was something more to it. Had the gravity been in the region of 1.064 I could safely write this off as a failure to accommodate for the brewhouse efficiency.

Question
So while I aimed for 1.085, after adjusting for a rough brewhouse efficiency of 75% I should have hit 1.064. I actually hit 1.050.

• Why was I so far off the mark?
• Are there any tips for consistently hitting high target gravities?