Missing pre boil gravity

[Porter0220]

I have brewed the below recipe twice and in both occassions have way undershot on my preboil gravity. I fixed the situation by boiling down to my desired pre boil gravity before moving forward with hops, but don't want to have to waste that time going forward.
Here is the recipe and process
Grain
17 lbs US 2 Row
1.0 lb Cyrstal 120
.75 lb Black Patent
.50 lb Flaked Barley
.25 lb Roasted Barley
.75 lb Lactose Sugar (5 mins before flame out)

Hops
1oz Bravo (60mins)
.75 Chinook (30mins)
English Dry Ale WLP002

Mashed Grains at 156 degrees for 1 hr in Cooler with bazooka tube.
Beersmith provided me the following values based on my set up
Strike water 5.68 gallons
Batch Sparge in 2 batches 2gal, 1.89 gal
Total Water approx 9.6 gallons
Pre Boil Volume should be 7gal
Pre Boil Gravity 1.082

in both batches i'm ending with a pre boil gravity of 1.065
I can only come up with 2 possible solutions
1) Too much water, which doesn't seem to be the case.
2) Very poor effeciency due to high grain bill

Any help on this would be great. This recipe came out great the first time but I would like to cut down on my boil time.

 

[doug293cz]

I plugged your numbers into my batch sparge simulator, and it comes out with a maximum pre-boil SG of 1.075 @ 100% conversion efficiency. I can't explain how Beersmith got its prediction of 1.082. I can explain my prediction, but it will be some time before I get it into writing.

In order to get a pre-boil gravity of 1.065, the conversion efficiency has to go down to 85%. This is pretty low. Homebrewers should be able to readily achieve conversion efficiencies of 95%, or better. The most likely culprit for the low conversion efficiency is too short a mash time for the coarseness of the crush. The coarser the crush the longer conversion takes. You also have a relatively thick mash (1.165 qt/lb), and this will slow down the conversion as well. To improve conversion efficiency, you should crush your grain finer and/or mash for a longer time.

There is a possibility that your sparging procedure could be less than optimal, which would drop the lauter efficiency from the predicted 76%. Can you describe your end of mash thru sparge procedures in more detail?

Brew on

 

[Porter0220]

Thanks for taking the time to respond.

I'm not overly scientific with my brews. I use beer smith 2

The mash did seem light on the water but I went with what beer smith said. I believe beer smith automatically defaults to a 72% efficiency.

I mashed for 60mins at 156 degrees.

I then batch sparged with 3.89 gallons which I split into 2 equal batches at about 168.
For sparging, first I vhourlaf, then empty the 1st mash to completion. I then add my 1st batch of sparge and stir for about 3mins. I then vhourlaf and drain to completion, same for the second batch.
The sparge water was barely enough to cover all the grains so I don't feel like I'm efficient in that area.

 

[Porter0220]

I'm crushing my own grain and it's quite coarse

 

[doug293cz]

Your sparge and lauter process looks sound. So your lauter efficiency should be close the the 76% the simulator predicts. That leaves conversion as your problem. You can mill finer and/or mash longer to improve conversion. You should also check that your mash pH (sample cooled to room temp) is in the range of 5.2 - 5.8, and 5.3 - 5.7 would be better.

You can monitor conversion during the mash using a refractometer and comparing your SG to the table here: http://braukaiser.com/wiki/index.php?title=Understanding_Efficiency#Measuring_conversion_efficiency.

Brew on