Efficiency Decreases as Grain Bill Increases

[d_striker]

We brew on a 5bbl system doing single infusion mashes. When brewing average gravity beers with around 300lbs of grain, our efficiency is pretty good at around 90%. It seems like whenever our grain bill surpasses 400lbs, our efficiency drops to the mid to low 80's.

I've analyzed data from our 20 previous beers and plotted data using parameters such as liquor to grist ratio, pH, mash temp, etc. I can not find a clear correlation between any of these parameters and the decrease in efficiency. The only common parameter in our batches with poor efficiency is the amount of grain.

Anyone else ever see this?

[Junkyard]

I see the same thing, I've always attributed it to extra grain bed compaction.. Can you fit the same Water to grist ratio of strike water in a 400 lb mash as you can in a 300 lb mash?

[d_striker]

I see the same thing, I've always attributed it to extra grain bed compaction.. Can you fit the same Water to grist ratio of strike water in a 400 lb mash as you can in a 300 lb mash?

400 lbs-yes. But it get's really close to the vorlauf outlet. Any more than 400 and I have to mash thicker.

I first thought that this was going to be the culprit, but after analyzing data, I couldn't really find a solid correlation...Even though most people say that a thinner mash will lead to higher efficiencies.

[AnthonyB]

This is just how things work… conceptually if you consider that there is extra grain in the mash but that you're still lautering with about the same amount of liquor, you can see that more sugars will be left behind. The only way around this is to increase the sparge volume which increases the pre boil volume which increases the energy expenditure. I would imagine in most parts of the US anyways, extra grain is cheaper than extra energy.

[d_striker]

This is just how things work… conceptually if you consider that there is extra grain in the mash but that you're still lautering with about the same amount of liquor, you can see that more sugars will be left behind. The only way around this is to increase the sparge volume which increases the pre boil volume which increases the energy expenditure. I would imagine in most parts of the US anyways, extra grain is cheaper than extra energy.

"This is just how things work" doesn't really illustrate the reality of the situation.

I suspect the aspect ratio of the MLT design is what you're alluding to? If this is the cause, I wish we would have gotten a 7bbl MLT.

[a10t2]

I suspect the aspect ratio of the MLT design is what you're alluding to? If this is the cause, I wish we would have gotten a 7bbl MLT.

To maintain efficiency, you would need a larger kettle, not a larger MLT. The cause of the efficiency drop, all other things being equal, is liquor absorption by the grist.

If you're trying to extract 5.5 bbl from a 300 lb grist, you'll need to use a total of about 6.7 bbl of liquor - the grist will retain ~1.2 bbl. Change it to a 400 lb grist, and you'll need 7.1 bbl of liquor. The more grist, the more liquor is retained proportionate to the total volume:

1.2/6.7 = 18%
1.6/7.1 = 23%

In order to keep the ratio constant, you would have to infuse a total of 8.9 bbl of liquor into the 400 lb mash, and boil off an extra 1.8 bbl relative to the 300 lb mash. (In reality, the numbers would be slightly different because the gravity contribution drops off throughout sparging, but hopefully this illustrates the concept.)

[d_striker]

Ah. That makes sense. Thanks.

[BDL]

Not too mention as grist increases you use more strike water to compensate for the additional grain, to maintain the same grist to water ratio. This means that you will also get less water to Sparge with, so the grain bed does not get washed as well as it would have otherwise, this coupled with what a10t2 has posted is what accounts for decreased efficiency, in addition to mash tun geometry, as they are really optimized for one sized load. If your drop off is only to mid 80's your still doing well. That's the nature of the game. Our old mash tun and our new mashtun both get low 90's doing 12 degree beers but when doing 18 degree beers the old one would drop to high 60's low 70's while our new MLT maintains an efficiency above 80. So it sounds like you have a pretty good setup.

[jwalts]

Here's a graph that crudely illustrates AnthonyB's and a10t2's spot-on explanations:

http://republicbrewpub.blogspot.com/2009/04/lautering-efficiency.html

Since the transition from first runnings to weak wort is gradual, water-to-grain ratio can make a huge difference as well. I'm still refining the numbers, but this chart illustrates the concept for an ideal lauter tun:



The WGR values are qt/lb at the start of lautering, so they include mash/lauter tun foundation water that gets recirculated during vorlauf. The kettle gravities are pre-boil. A practical takeaway is that you can't hit certain gravities without thickening the mash. As a guy who loves fermentability, I shake my fist at that tradeoff.

Joe

[polynomial]

Here's a graph that crudely illustrates AnthonyB's and a10t2's spot-on explanations:

http://republicbrewpub.blogspot.com/2009/04/lautering-efficiency.html

Since the transition from first runnings to weak wort is gradual, water-to-grain ratio can make a huge difference as well. I'm still refining the numbers, but this chart illustrates the concept for an ideal lauter tun:

[ATTACH]18208[/ATTACH]

The WGR values are qt/lb at the start of lautering, so they include mash/lauter tun foundation water that gets recirculated during vorlauf. The kettle gravities are pre-boil. A practical takeaway is that you can't hit certain gravities without thickening the mash. As a guy who loves fermentability, I shake my fist at that tradeoff.

Joe

just had to say thanks for this post, great science!