Help me troubleshoot low efficiency?

[Mike_A]

I'm relatively new to AG brewing and my efficiencies are all over the place, according to BeerSmith's predictions. My first batch was a SMaSH that supposedly had 83% efficiency, and now my fifth batch has an efficiency of just 66%. Here's what I did this time, recipe based on national home brew day's "Must be the season of the Wit":

Batch size 11 gal:
10 lb pale 2-row
1 lb flaked wheat
5 lb torrified wheat
4 lb white wheat malt
1/2 lb rice hulls
1oz liberty plug @ 60min
1oz willamette plug @ 15min
Target OG (assuming 80% efficiency): 1.053
Actual OG: 1.044 (66% efficiency)

My mill was set at 0.039" gap for all grains, but after milling once I decided to close the gap slightly to 0.036" and re-mill all the grains (except flaked wheat). The crush after that looked good to me - no intact kernels, husks were separated but not shredded. Wheat kernels were cracked but not pulverized.

Infusion mashed at 1.6qt/lb (33qt strike water @ 153*F) at 145*F for 60min. Actual temps fluctuated 143-148*F. Stirred mash occasionally and recirculated with a pump. Stopped stirring & recirculating entirely 20 mins before sparge. My MLT has a full false bottom and I fly sparged with a 1/2" silicone tube at a rate of 1.35 qt/min into a diffuser dish which helps disperse sparge water evenly over the grain bed. Grain bed was approx 5" thick. Sparge took 40min total and did not get stuck at all.

Sparge water was 170*F, achieved preboil volume of 13.5gal. Boiled 60min, ended up with 12gal. After trub, chiller and shrinkage losses I had a hair over 11gal. Chilled a little too low to 60*F, where I took my hydrometer measurement.

I could use some help figuring out what went wrong here, and I'm sure there's some information I haven't included that may be pertinent.

 

[AKnewbrews]

Was the original recipe for 11 gallons, or did you compensate your grain bill for 11 gallons? 11 gallons seems like an odd final volume to me. Something I wouldn't just shoot for unless there was a certain purpose.

 

[Mike_A]

The original recipe was for 5.3 gallons but I modified/scaled it for 11 gallons final volume. I split the batch into two fermenters and like to have 5.5 gallons in each, so I end up with 5 gallons after racking to secondary and kegging. I allow for myself to leave behind at least a quart in yeast/trub in each fermenter each time.

 

[ajf]

In my experience, your efficiency will vary a bit while you are getting to know your equipment and procedures. As you get more familiar with the process, the efficiency variations will reduce.
There are also other factors that can affect efficiency.
1. Making a higher gravity beer will usually result in lower efficiency.
2. Making different batch sizes can result in efficiency changes as the dead space in your equipment (which is constant) will account for a different percentage of the batch size.
3. Using different grains can affect efficiency as they could need to be milled differently to account for the different grain sizes.
4. Changing equipment or procedures often affects efficiency.

Taking notes is the best way I know of to account for these variables, along with going back to those notes to see what sort of efficiency you got last time you brewed a similar beer, and taking into account efficiency improvements that occur over time.

-a.

 

[Mike_A]

Thanks ajf, I understand what you mean. What really grinds my gears about this batch is that I hit everything else I aimed for dead on. The strike/infusion temp was spot on, I maintained relatively consistent temps compared to my previous batches (which all had 75%+ efficiency), the crush looked great, the sparge went very smoothly, I obtained a good pre-boil and post-boil volume for what I was aiming for...

Compared to this batch, I've had more complex grain bills, higher OG's and less consistency in control of the mash/sparge, yet still ended up with relatively crappy efficiency.