Another batch, another question

Is that 4.25 gallons of wort into the fermenter, or in the kettle after the boil? If the former, what was the volume in the kettle? (i.e. did some wort stay behind in the kettle?)

 

So, when computing mash efficiency, you need to know the post boil volume in the kettle. Just trying to scope the size of the problem. Do you know what was in the kettle?

 

How many ounces of hops were in the boil, and what kind (i.e. leaf or pellet)?

 

Ok, so estimating....
4.25 gallons + 0.03125 gallons (sludgy trub) + 0.125 gallons hop absorption =
~ 4.41 gallons post boil

What was the temperature of your post boil wort when you measured the gravity?

What was your pre-boil volume? And at what temperature was the pre-boil wort when you measured its gravity?

 

Your not taking the water absorbed by the grains during the mash into account.

 

@butterygold Was 7.5 gallons the total amount of water you used? Or did you have 5 gallons of wort left in the kettle after hoisting the bag, which you then dunked in 2.5 gallons of water?

 

I'm still not clear, but bear with me, because it matters for figuring out what the mash efficiency actually was...

5 gallons in the mash
pulled bag and dunked in 2.5 gallons
0.5 gallons came from where? New added water?

 

OK, so it sounds like you're not taking the malt absorbing some of the water into account, but further clarification may help. I would expect to lose 2-3gal to the grain with that amount, depending on freshness and how patient I was with runoff. Did you measure the total volume of wort you had before you started the boil?

 

Ok. The 0.5 gallons was additional water, into the big (not the small) kettle. So let's say there was a total of 5 + 2.5 + 0.5 = 8 gallons of water used.
Lets estimate that 16 lbs of grains trapped about 1.9 gallons of liquid (0.12 gallons per pound). So...

8 - 1.9 = 6.1 gallons pre-boil kettle volume

So, if your pre-boil was 6.1 gallons and the gravity was 1.036 at 152F, corrected for temp to 1.056:
6.1 x 56 = 342 points

And post boil was 4.41 gallons and the gravity was 1.059:
4.41 x 59 = 260 points

Should be the same points for both, but the big difference tells me there is something off in one or more estimates or measurements somewhere.

Using your post boil numbers and reasonable assumptions about your grains (PPGs), I'm calculating about 45% Mash efficiency. Using your pre-boil numbers, I'm calculating about 59% mash efficiency.

Neither number is great, but 59% is a whole lot better than 45%. Again, the fact that they are different points to an error somewhere.

Are you sure the pre-boil wort was really at 152F (mash temp) when you measured the gravity, and hadn't lost some heat? If it had, that would make the adjusted-for-temp pre-boil OG and mash efficiency lower (i.e. would make the pre-boil measured mash efficiency closer to the post boil measured mash efficiency).

A few thoughts.

- Any measurement error... weight of grains, wort volumes, temperatures, hydrometer readings... affect the computed mash efficiency

- You say you used the finest setting on the mill. What did the crushed grains look like? Perhaps take a picture next time.

- How sure are you of your actual mash temperature? How much did it vary? Is your thermometer calibrated? How did you maintain the temperature? (If you were very far off, you could have got poor conversion.)

- Who weighed your grains and how?

 

If i made this recipe batch sparging it would be something close to 7-1/2 gals for mash and 2/3 for sparge. Collect 7/6-1/2 and boil to about 6/5-1/2 depending on gravity.

 

Get a wooden dowel. Add "X" gallons of water to the kettle, dip the dowel, and mark it at the water line. Measure smaller increments proportionally (by length) and mark them.