Low OG

Do some calculations or use some good brewing software. There's no reason to run into this situation again.

 

Adding all your water to the tun is the no-sparge technique ==> generally lower efficiency all else equal.

Ignoring fly-sparging, double batch-sparging is the way to go to get the most sugar from your mash.

 

Finer milling of the grist...tweaking your strike water with salts and minerals...and the proper sparge water temperature can increase your pre-boil extract eff.

 

I think you have used water in wrong ways, your water/grain ratio at mash in was 2qts/Lb(too much) . Then you added 2 more gals for sparge water leaving 0.5 gal in the tun, maybe this 0.5 gal had sugars in it.
The total result is you have used 12 qts of water to mash and sparge 2.1 lbs of grain (5.7 qts/lb)and have collected 8 qts of wort (1.5 qt water/1qt wort).
When I mash and sparge I use 15 qts of water for 11 lbs of grain(1.36 qt/lb) for mash in and 22 qts for sparging, these numbers give me a total of 37 qts of water (3.36 qts/lb)to get 29 qts of wort (1.275 qt water/1 qt wort) .

Maybe this could help to understand why you didn´t get a higher wort gravity. As many others have said above it could be possible you had some issues in regards Ph mash due the use of wheat malt, thus a poor extraction could have been feasible

 

This!!! And damn, it took a long way into the thread for someone to notice! This is way too thin of a mash, I don't know if this is past the point where it is too thin for proper enzymatic activity, but based on the reported efficiency I'm guessing it is close. Thinner mashes are always less efficient (since you get more diluted first runnings), but with what the OP describes it is probably both messing with conversion and the actual efficiency of washing sugar out. Add to this the above mentioned pH issues that large amounts of wheat can cause (not usually this significant, but my wheat beers are always a bit less efficient) and I think we have the OPs problem explained.

So, to the OP: mash as a standard thickness and use some acid malt when brewing with wheat and you should be able to improve you efficiency massively.

 

Ok, after thinking about this for a few minutes I might be off base... The efficiency issue of thick VS thin mash may only apply when trying to achieve a very high gravity wort. I've never had efficiency problems with low gravity brews and have mostly thought of mash thickness issues in terms of brewing something like an imperial stout or barleywine... so what I said may not apply in the OP's case. I still think 2qt/# is too thin, but I'm not sure if thats whats killing his efficiency, anyone else have any thoughts on this?

 

I agree... 2 qts/lb should not ahave a large impact on conversion efficiency.

 

How long did you mash this batch?

 

I guess your mashing time was not enough to full convertion of starches.

By John Palmer :

The grist/water ratio is another factor influencing the performance of the mash. A thinner mash of >2 quarts of water per pound of grain dilutes the relative concentration of the enzymes, slowing the conversion, but ultimately leads to a more fermentable mash because the enzymes are not inhibited by a high concentration of sugars. A stiff mash of <1.25 quarts of water per pound is better for protein breakdown, and results in a faster overall starch conversion, but the resultant sugars are less fermentable and will result in a sweeter, maltier beer. A thicker mash is more gentle to the enzymes because of the lower heat capacity of grain compared to water. A thick mash is better for multirest mashes because the enzymes are not denatured as quickly by a rise in temperature.

As always, time changes everything; it is the final factor in the mash. Starch conversion may be complete in only 30 minutes, so that during the remainder of a 60 minute mash, the brewer is working the mash conditions to produce the desired profile of wort sugars. Depending on the mash pH, water ratio and temperature, the time required to complete the mash can vary from under 30 minutes to over 90. At a higher temperature, a stiffer mash and a higher pH, the alpha amylase is favored and starch conversion will be complete in 30 minutes or less. Longer times at these conditions will allow the beta amylase time to breakdown more of the longer sugars into shorter ones, resulting in a more fermentable wort, but these alpha-favoring conditions are deactivating the beta; such a mash is self-limiting.

A compromise of all factors yields the standard mash conditions for most homebrewers: a mash ratio of about 1.5 quarts of water per pound grain, pH of 5.3, temperature of 150-155°F and a time of about one hour. These conditions yield a wort with a nice maltiness and good fermentability.

 

If batch sparging, you want to add water hot enough to bring the grain bed and wort up to 170F. (Actually, I target 168F, but same idea.) This is called a mash out.

 

Get ye the FREE and oh-so-easy to use Bru'in Water spreadsheet along with a Ward Laboratories home water test (W-6 Household Mineral Test 21.00 includes sample bottle and shipping).

You want to add sparge water hot enough to raise the grain bed temperature into the upper 160s but no more than 170°F.

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Trail and error will get you dialed-in to the best sparge water temperature.
Measure the pre-sparge grain bed temperature.
Add hot water above the target temperature (168°F).
Measure grain bed temperature.

Next brew day: Rinse. Lather. Repeat.

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Over a few trials, I discovered my 1st sparge water needs to be 2.7 times the difference between the post-1st running's grain bed temperature and the sparge water temperature.

Ex.
Post-1st running's grain be temperature: 148°F
Target grain bed temperature: 168°F
Diff = 20°F

1st sparge water temperature = 148°F + (20°F * 2.7) = 202°F

The 2nd sparge factor is 2.5.
Post-2nd running's grain be temperature: 164°F
Target grain bed temperature: 168°F
Diff = 4°F

2nd sparge water temperature = 164°F + (4°F * 2.5) = 174°F

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The 2.7 and 2.5 multipliers work on my system.
YMMV.