Efficiency question/misunderstanding

[t_stout]

Okay so I am a little confused about my efficiency #'s, and how they seem too low. Using beersmith2 and here are my last two brews:

1: 2 hearted clone
Brewhouse efficiency: 72%
Est Pre-Boil Gravity: 1.053
Measured Pre-Boil Gravity: 1.050
Est Pre-Boil Volume: 7.89G
Measured Pre-Boil Volume: 7.75G
Est OG: 1.064
Measured OG: 1.059
Est Batch: 5.5G
Measured Batch: 5.4G
Mash Efficiency: 79.6%
Total Efficiency: 65.4%

For my 2nd brew I lowered my brewhouse efficiency to 67%

2: Tank 7 clone
Brewhouse efficiency: 67%
Est Pre-Boil Gravity: 1.062
Measured Pre-Boil Gravity: 1.060
Est Pre-Boil Volume: 7.89G
Measured Pre-Boil Volume: 7.77G
Est OG: 1.075
Measured OG: 1.075
Est Batch: 5.5G
Measured Batch: 5.2G
Mash Efficiency: 75.6%
Total Efficiency: 63.3%

So the bottom line: For my second batch I was closer to my est pre-boil volume, closer to my est pre-boil gravity, closer to my est OG (hit it perfectly ), the only thing was that I put a little less into my fermenter (5.2G vs 5.4G on 1st brew). Why is my efficiency lower than the 1st batch? I'm especially confused about the mash efficiency. I would think that would FOR SURE be higher for the 2nd batch. Is this due to the fact that I lowered my brewhouse efficiency for the 2nd batch? Anyway, sorry for the novel. If anyone could give me some insight that would be awesome. Thanks!!

 

[Northcalais40]

The efficiency isn't outragiously varied, or very low so I wouldn't be too concerned. A possible factor is the difference in OG and the associated sparge volume. I assume that you would have a lower sparge water volume, which would give you a slightly lower efficiency. There are so many other variables involved though so I would say that you did quite well enough.

 

[t_stout]

Yeah for brew 1 mash vol=4.28G and sparge vol=5.29G. For brew 2 mash vol=5.21G and sparge vol=4.71G. Also for brew 1 I did mash out, single batch sparge and for brew 2 I did no mash out, double sparge. I'm just confused about why beersmith is saying my efficiency is LOWER for brew 2 given that it seems I hit my numbers way better.

 

[erikpete18]

I think it does come down to the amount collected in the end. Although it looks like you're consistent, so I wouldn't suggest changing anything, but just for academics, here's how I'd break it down.

For batch one, figure out the total amount of possible points. From the expected OG (64), expected batch size (5.5) and expected efficiency (0.72), you get a total of (64*5.5/0.72) about 489 possible points. However, you were only able to obtain an OG of 59 in a volume of 5.4, giving you (59*5.4) about 318 points. Taking the results gives you an efficiency of (318/489) about 65%.

For batch two, you had a possible extraction of (75*5.5/0.67) 616 points, but only extracted (75*5.2) 390 points, giving an efficiency of 63%. While your OG was on target for batch two, because you're a third of a gallon short, your efficiency is a little lower. You can also look at it as diluting up to 5.5 gal. If you diluted your 1.075 batch to 5.5 gal, you'd wind up with an OG of about 1.071, lower than the expected level of 1.075 using your predicted efficiency.

Of course this is just the math behind it. The reasons that your efficiency might be low are wide-ranging. But like I said, about 65% isn't anything to sneeze at, especially if you're able to keep that fairly consistently, which it looks like you are based on this small sample size. If anything, blame the slightly lower efficiency for batch two on the fact that its a stronger beer, plan ahead for that in the future, and keep doing what you're doing!