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Efficiency too high - what's wrong?

I am fairly new to AG, this was my 6th batch and was the Oatmeal Stout NB kit. The target mash temp was 153, but I hit 155. Batch sparge with first runoff 3.3g and 2nd runoff 2.9g. Mashout temp was 169 (10min). Runoff was about 10 minutes for both. Below are my calcs with the max ppg from Table 27 in Palmer’s book. Hydrometer accurate to within 1 point at different temps. Volume to kettle=6.2 gallons SG=1.050 (volume measurement accurate to within a pint or so).

Grain max ppg
6.5# English Marris Otter 37 x6.5/6.2 = 38.8
1# Flaked Oats 32 x1/6.2 = 5.2
0.5# Eng Roasted Barley 25 x0.5/6.2 = 2.0
0.5# Eng Choc Malt 28 x0.5/6.2 = 2.3
0.5# Eng Dark Crystal 33 x0.5/6.2 = 2.7
Maximun points = 51

Efficiency = 50/51 x 100 = 98%

  1. Did I do the calculation correctly

  2. I didn’t think to weigh the grain as it was ordered pre-crushed. Am I correct in thinking that they must have supplied more grain?

  3. Or was my mash temp simply too high and expect this beer not to be good (time will tell).

My grain mill is on order and this was my last kit brew.
Thanks, Mike

I think your calculation is right, they must have added a couple extra pounds of base malt. Either that or your OG reading is somehow off. Changing mash temp a few degrees doesn’t really change efficiency much.

Looks like a very nice recipe, even with extra base malt it should be just fine.

Are you sure you actually had 6.2g in the kettle? Getting your volume bang on for a new AG brewer is hard to do given all the variables in play. It’s basically impossible for a homebrewer to get 100% efficiency.

The best way to measure efficiency in my opinion is to measure your volume and SG in the fermenter. Compare that to the recipe and adjust to calculate your efficiency. Efficiency needs exact volume as well as a temperature-corrected reading.

You should get a pre-boil gravity reading to get your mash efficiency. Evaporation during the boil is a difficult variable to control.

I’m guessing that this is the error. I didn’t weigh the grain as it was a kit. I didn’t think they would give me extra. Next time I’ll be sure to check that.

The volume measurement was withing a pint or so. I had carefully made a calibration stick a half gallon at a time for this kettle using a measured amount of water that was weighed for accuracy.

Yes, the reading was pre-boil.

Thanks for all the replies. I just wasn’t sure if I was missing something. But it must be an error in the grain quantity. Hopefully the extra they gave me was base malt and not the roasted or chocolate stuff. I’m soon to have total control over the grain. Mill is on the way and I’m putting in my grain order at my LHBS. One thing still bothers me is that if there was extra grain, then I should have had more grain absorbtion in the first runoff. I had only 0.1 gal/lb absorbtion (0.4 qt/lb) based on the kit quantity of 9 lbs of total grain. This absorbtion is typical of my previous batches since I have been running about 0.125gal/lb average. I’ll find out in about 6 weeks during tasting if something is really screwed up. I’ll repost at that time.
Thanks again.

How did you take your sample? If it was pre-boil and drained some from the bottom of the kettle without mixing it up really well, you can get a higher gravity reading due to stratification of the wort (more sugar concentrated at the bottom with the initial runnings).

Did you take the volume reading hot? That’d give you 4% more volume.

It was preboil at 150 degrees or so, but I cooled the sample before taking the gravity reading. I did mix the wort in the kettle quite well and dipped the sample from the top immediately after mixing.

If I used a 4% lesser volume in the calculations, the max points would be 53 vs 51 and still put the efficiency calculation at 50/53 x 100 = 94%. Must have been extra grain in the kit. That won’t happen again when my mill arrives this week!

Thanks for the replies!

You need to be sure and cool your gravity sample in a jar with a lid or in a syringe or something that prevents evaporation. If you let it cool open it will read up to 4 points (1°P) higher, IME. See this thread where Kai was having the issue:


[quote=“tom sawyer”]Did you take the volume reading hot? That’d give you 4% more volume.[quote=“TrapperMike”]
If I used a 4% lesser volume in the calculations, the max points would be 53 vs 51 and still put the efficiency calculation at 50/53 x 100 = 94%. [/quote] [/quote]
Water is 4% less dense at 100°C, but at 60°C it’s only 2% less: ... er_and_ice

How about 60-70F? Thats where you’d want to get your volume reading.

94% I could almost believe, especially if the malts had a little more starch than the default values used in the potential extract calculation.

At 20-25°C it’s 99.8-99.7% of full density, so if that’s where you measured it cold then you would scale there instead of 100%. So 98% at 65°C becomes 98/99.7 = 98.3% of the density at 25°C. Either way, scale based on your sample temp, it’s somewhere between 2 and 4% from mash temps to boiling.

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