first wort gravity and mash efficiency

**Kaiser** · 06-09-2008, 01:34 AM

So I'm trying to come up with a way to determine mash and lauter efficiency separately. Not because I have problems, but to provide better means of troubleshooting brewhouse efficiency. I define mash efficiency as the ratio between the extract that was dissolved into the mash and the maximum extract that was available in the grain. Lauter efficiency is the ratio between the extract that made it into the kettle and the extract that was dissolved into the mash. The product of both is the brewhouse efficiency and that is the efficiency that most of us report, brag or complain about and use to size recipes.

The motivation for this stems from the fact that both efficiencies are affected by different parameters are need to be addressed differently. If there are shortcomings in your mash efficiency, you should not make up for them by sparging more as this may lead to oversparging problems. Similar, lauter efficiency problems cannot be compensated for with increasing the mash efficiency if that is already 100%.

To measure the mash efficiency I think that taking a gravity reading of the first wort should give you an idea where you are. If there is 100% mash efficiency, the extract content (=gravity) of the first wort in Plato should be:

FW extract in Plato = (grain weight in kg * 0.8 ) / (grain weight * 0.8 + strike water volume in l)

The 0.8 multiplier for the grain weight is the laboratory extract of that grain. For most base malts its 80% or close. The water volume is the volume of all the water (including water added by batch spargers to equalize run-offs) added before stirring and taking a gravity reading. Your mash efficiency is now the measured extract vs. the calculated extract. It should be close to 100%. This works well for those of you who have a refractometer as you can actually take gravity readings fairly easily.

When I brewed my Helles this weekend, I added 17.5l of water, had 4.0kg of grain and got a FW gravity of 16 Plato. The expected FW gravity was actually 15 Plato, but I contribute this to measurement errors and try to do better next time around as you mash efficiency is unlikely to exceed 100%.

So if your brewhouse efficiency is low, or you are just curious, you may want to give this a try. And if the FW gravity/extract is significantly less than what you expected the following parameter can have something to do with that:

- pH
- crush (though I'm starting to get convinced that this should not have as big of an impact as it is reported)
- mash-out (can access starches that single infusion cannot)
- time

Kai

**BeerCanuck** · 06-09-2008, 02:37 AM

That makes allot of sense Kaiser.

Cheers
BeerCanuck

menschmaschine · 06-09-2008, 12:47 PM

Quote:

Originally Posted by Kaiser

- crush (though I'm starting to get convinced that this should not have as big of an impact as it is reported)

I've been suspicious of this myself. I suspect that pH is more important than convention has shown... as far as converting sugars in the malt goes. I don't think a few points finer on the crush is going to exponentially increase your efficiency, as is implied by many homebrewers. Efficiency can be broken down into 2 categories... getting the sugar from the grain and getting the sugar into the kettle. Understanding what affects each of these is what's important in efficiency. Good work Kai.

**Kaiser** · 06-09-2008, 01:49 PM

Quote:

Originally Posted by menschmaschine

I don't think a few points finer on the crush is going to exponentially increase your efficiency, as is implied by many homebrewers.

Yes it shouldn’t. Malt specs show the efficiency difference between coarse and fine crush, and this is always below 2% for modern malts. I suspect that the coarser crush makes an existing problem (pH for example) worse and that that causes the big efficiency difference between fine and coarse crush that many brewers see. I plan to run a few small scale mashing experiments with different mash pH levels and I’m particular curious about this as well.

I have also read papers where the malt was crushed at a gap as large as 31 mil and their reported efficiency was just fine (90% +).

Kai

menschmaschine · 06-09-2008, 02:13 PM

Quote:

Originally Posted by Kaiser

I plan to run a few small scale mashing experiments with different mash pH levels and I’m particular curious about this as well

VERY interested to see the results of that.

**McKBrew** · 06-09-2008, 02:24 PM

I'd also be interested in seeing how different manifold types play into this equation. Maybe not at all.

I obtained 64% efficiency this weekend.

1) I mashed for 90min.
2) I did 2 equal batch sparges
3) I used PH 5.2 in the mash
4) My crush looked pretty comparable to the "good crush" pics posted in the forum.
5) I have a single bazooka screen running down the center of my MLT.

Based on all of that, I should be able to get better efficiencies. I'd be happy with 75%.

menschmaschine · 06-09-2008, 02:27 PM

Just to add...

Is it safe to say that a longer mash time could potentially compensate for a coarser crush? Mash chemistry aside, take a single-infusion mash, for example. The typical homebrew schedule is 60 minutes. When in reality, full conversion is probably achieved in maybe 20-45 min. So, one would think that, if a longer mash time can compensate for a coarser crush, that extra 15+ minutes of mash time should compensate unless your grain is barely crushed, making the case for crush and efficiency more minimal.

**Kaiser** · 06-09-2008, 03:20 PM

Quote:

Originally Posted by McKBrew

I'd also be interested in seeing how different manifold types play into this equation. Maybe not at all.

When batch sparging, the manifold design doesn’t have any impact on the efficiency. For what it is worth, you could be lautering through a single hole. It has an impact on the flow rate though and when your mash gets stuck you may end up leaving more wort (i.e. extract) behind than intended. In batch sparging the “rinsing” of the sugars happens when you stir in the sparge water.

Quote:

I obtained 64% efficiency this weekend.

Is this number based on what was in the boil kettle or what ended up in the fermenter. If it is the latter, how much was left in the boil kettle?

What temp did you mash at and did you do a mash out? Next time you may want to keep track of the water volume added before the first run-off and measure the gravity of the first run-off. I’m curious if you are loosing efficiency in the mash.

Menschmachine,
Yes, I think a longer mash could compensate for the crush. If you have a refractometer, you can easily take a reading (after stirring the mash) every 15 min and you will see how the extract content slowly goes up. If you are not near the calculated maximum after 60 min, add another 15 and see if that changes anything.

Kai

**Bobby_M** · 06-09-2008, 03:25 PM

I think the most accurate way to measure mash efficiency is to take the gravity sample directly out of the mash tun and use the strike volume in the efficiency calculation. First wort is going to be AFTER absobtion. Technically any wort locked in to the grainbed is still valid as a mash efficiency.

**Kaiser** · 06-09-2008, 03:43 PM

Quote:

Originally Posted by Bobby_M

I think the most accurate way to measure mash efficiency is to take the gravity sample directly out of the mash tun and use the strike volume in the efficiency calculation. First wort is going to be AFTER absobtion. Technically any wort locked in to the grainbed is still valid as a mash efficiency.

If there is an error because of absorption, shouldn’t that affect both the first wort and the gravity in the mash? In other words, why should mash gravity be different from first wort gravity?

Or do you mean with absorption the amount of wort kept in the grains after it has been drained completely? For that reason I did say that you should take the amount of water that was added and not the volume you ran into the kettle.

Kai

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