Getting crap efficiency on a few brews.

So I've been getting about 50-60% efficiency on a few brews lately. I need some help troubleshooting the problem.

I've got:
2 10 Gallon rubbermaids, one is just an HLT and the other is false bottomed.
I fly sparge.
The grains are not crushed by me, but rather my home brew store. I do not know if it being done correctly.
I have missed my mash before on all of my brews, but only by 2 degrees at most.
I raised my sparge water to 175/180 to try to help get better numbers. It help a little but not much.

My usual brewing schedule includes:
Raising water to mash temp and getting 1.3-5 qts per pound of grain
Mashing at rest temp for 60 minutes
Heating sparge water
Setting up sparge system
rinse grains with 1 inch of water over the grain bed at all times.
Balance valves and then wait until I hit my preboil volume. Usually like to make it go as slow as I possibly can. I usually take an hour to sparge.
take pot and boil for 60 while adding anything that is required.

I did Biermuncher's Centennial Blonde and got a 1.21 as my preboil gravity. I skimmed off the top and the wort was at about 140. Don't know if that is the right way of doing it.

What was different about these brews than the others? If they were significantly darker or lighter, it could be a pH problem.

Take a look at some pictures of a good crush (I don't have any, but they're floating around on this site somewhere). I've found that the crush makes a huge difference.

If the crush looks okay, try batch sparging on your next brew. If you get better efficiency, the problem was with your mash/lauter tun (probably channeling). For mash tun efficiency information, listen to THIS.

Good luck!

Preboil gravity has to be taken from a well mixed kettle full of wort. You can't skim anything because it's going to be highly stratified.

There are three key things that you have to have to calculate accurate efficiency numbers:

1. You must be able to measure all of your volumes accurately. When you measure a wort's gravity, the volume of the wort is just as important as far as calculating efficiency.
2. You must be able to measure gravity accurately (usually not a problem with a good hydrometer or a refractometer) and account for temperature variations.
3. You must have the gravity potential of the grain you are using. If you think your grains are giving you 37 points per pound per gallon (PPG) and they are really only giving you 35 PPG, then your calculated efficiency will be artificially lower. Conversely, if you count on 35 PPG and your grain gives you 37, your calculated efficiency will be artificially high.

Using guestimations or approximations when trying to calculate efficiency will have a significant effect on the final result.

If you have changed grain batches or brands recently, it might be that the new grain just doesn't have the gravity potential that you think it does. I encountered this with a bag of Breiss malt. Efficiency measured about 5% lower than normal. In reality, it was just wimpy malt and I wasn't accounting for the lower yield. When I switched to Fawcett Marris Otter, my measured efficiency went right back up, all other processes remaining the same.

It sounds like all your processes are fine. Get the actual malt specs if you can and just for grins, try milling the grain twice on the same setting. The second pass will separate the husk from the kernel which is what you want. You know it's time for a grain mill, don't you? :cross:

Prosit!