I read the thread on mash efficiency and found it very interesting. I aim for 70% efficiency but I rarely seem to hit it. More often than not I'm in the high 60s. Yesterday, I brewed an amber ale. My mash water temp was a bit high to start at around 158F, but I left the lid off and did a bit of stirring and after 20 minutes it dropped down to 152F. When I added the sparge water, the temp was 170F. When I took a pre-boil reading, my gravity was 1.039, which was only a point off the 1.040 I was aiming for. I did a slightly longer boil than the usual 60 minutes hoping to gain that point back. My post-boil gravity was 1.048 instead of the 1.050 I was aiming for.
I'm brewing 2.5 gallon batches and I use a 5 gallon Igloo water cooler for a mash tun. When I was cleaning up, I filled the cooler with cold water to cool the grains down. Just on a whim, I got the hydrometer out and took a reading of the cold grain mix. I got a reading of 1.004.
Here is my question. I realize I'm not ging to get ALL the sugars out of the grains, but I was kind of surprised there was still that much sugar left. Or, would that be a 'normal reading' and I'm seeing a problem where none exist?
If anyone has any insights, I would be grateful. Thanks.