Imp. Stout Efficiency and Boil Time

[doug293cz]

It really depends on what your last running's OG is. If it's still quite high there is something to be gained from an extended sparge and boil, if it's already mostly water than it's a waste of time and energy at best. I would plan on the extended mash and boil only on a contingency basis by having a couple of gallons extra sparge water ready. When you're nearing your target volume you should take a sample of the runnings, stop the sparge, measure its OG and then decide whether to go with the extended sparge.

I'm gonna take a guess and say that if OP measures the instantaneous runnings SG when he has collected the usual pre-boil volume that he would for a 1 hour boil, the SG will be above 1.050.

@Rob2010SS : are you willing to check this and report back here?

Brew on

 

[Rob2010SS]

I'm gonna take a guess and say that if OP measures the instantaneous runnings SG when he has collected the usual pre-boil volume that he would for a 1 hour boil, the SG will be above 1.050.

@Rob2010SS : are you willing to check this and report back here?

Brew on

Yeah, not a problem. I'll report back what I find.

 

[doug293cz]

Ran a couple of simulations to see what effect additional sparging might have for the OP's case: 55.5 lb grain bill, 1.1 qt/lb mash thickness, 95% conversion, 12.5 gal post-boil, 1 hr vs. 3 hr boil @ 1.25 gal/hr boil off rate. Used a triple batch sparge to approximate fly sparge (will be somewhat pessimistic.)

For 1 hr boil, OG is 1.100 - 1.101, and mash eff. is ~64%. (final runnings SG =~1.063, points collected = 1255)

For 3 hr boil, OG is 1.109 - 1.110, and mash eff. is ~70%. (final runnings SG = ~1.051, points collected = 1372)

The extra points from additional sparging are the equivalent of 2.66 lb of DME.

Brew on

 

[Rob2010SS]

In an imperial stout, if one went the route of adding DME to makeup the points, what kind of DME would you add? Something similar to the base malt?

 

[day_trippr]

I would go with pilsner or very light DME, to minimize the addition of dextrins found in darker blends...

Cheers!

 

[eric19312]

In an imperial stout, if one went the route of adding DME to makeup the points, what kind of DME would you add? Something similar to the base malt?

yes - light DME would be fine.

 

[Rob2010SS]

I'm gonna take a guess and say that if OP measures the instantaneous runnings SG when he has collected the usual pre-boil volume that he would for a 1 hour boil, the SG will be above 1.050.

@Rob2010SS : are you willing to check this and report back here?

Brew on

@doug293cz Brewed this up over the weekend. My initial planned pre-boil volume was 13.5. At 13.5 gallons, I pulled a sample of the runnings and checked gravity. At 133F, my hydrometer measured 1.048, which is 1.060 when corrected for temp. However, I don't think my hydrometer measures correctly that high. I ran into an issue on my last brew with converting a higher temp sample. But anyway, in answer to your question, yes, it appears the runnings at my usual pre boil volume were above 1.050.

 

[Vale71]

Looks like you can make another batch with second runnings.

We've also ruled out channelling in the grain bed which would have caused OG to drop more significantly.

 

[Rob2010SS]

Yeah, I definitely could have. Unfortunately, I was not setup for that so I did not keep the second runnings. I collected an extra gallon and boiled for an extra hour but the rest got dumped.

Yeah this sparge took about 65 mins to complete so it wasn't fast by any means.

 

[Erik the Anglophile]

Borrowing the thread a little if it's ok? , gonna brew a porter with an OG of around 1065 tomorrow, should i adjust for lower efficiency or does that only really appky when you come up to really heavy gravities like 90 and upwards?

 

[Qhrumphf]

What gravity do you normally brew around?

If you're normally brewing 1.055 probably negligible difference. 1.040 you might notice it more. Also depends on how dialed in your system is. If your efficiency is very consistent you're more likely to notice it than if you already have wide swings in your efficiency.

 

[Erik the Anglophile]

What gravity do you normally brew around?

If you're normally brewing 1.055 probably negligible difference. 1.040 you might notice it more. Also depends on how dialed in your system is. If your efficiency is very consistent you're more likely to notice it than if you already have wide swings in your efficiency.

My "system" (wich is basically an isolated picnic cooling bag as mash tun and a fermentation bucket with holes in the bottom inside a fermentation bucket with a tap) is dialed in for about 75%eff wich I adjust my recipes for. Have only done 4 all grain brews around 40-50 OG and it has been pretty accurate so far. I'm thinking about doing the mash a bit thicker(2.1-2.3 liter/kg malt) instead of my usual 2.6-2.8 to be able to sparge it properly.

 

[VikeMan]

Borrowing the thread a little if it's ok? , gonna brew a porter with an OG of around 1065 tomorrow, should i adjust for lower efficiency or does that only really appky when you come up to really heavy gravities like 90 and upwards?

Good question. You might hear folks say thing like "I always get 75% mash efficiency, except when I do really big beers, then I get 65%." But it is definitely not a step function.

All other things being equal (same batch size, boil length, etc.), a batch with a larger grain bill will have a lower mash efficiency than a batch with a smaller grain bill. Here's a C&P from a presentation on mash efficiency:

"Recipes with larger grain bills (but the same pre-boil volume) require more total water, because of more grain wort absorption. So the ratio of absorbed wort to total wort (including absorbed) is larger. Therefore a smaller percentage of the total sugars/dextrins produced makes it to the kettle. The math (which also takes into account other types of losses at the mash/lauter stage) is fairly complicated. (BrewCipher includes a sheet for estimating mash efficiency changes when changing grain bill size and/or sparge method.)"

 

[Erik the Anglophile]

Beersmith's estimated mash efficiency is at 75%, wich is what it usually is and it has been correct this far. I'll go with that and adjust it if OG comes out a bit lower than expected.

 

[VikeMan]

Beersmith's estimated mash efficiency is at 75%, wich is what it usually is and it has been correct this far. I'll go with that and adjust it if OG comes out a bit lower than expected.

If your normal mash efficiency is 75% for a 1.045 wort, and you're doing a 1.065 wort, expect a fairly significant decrease. In my setup, that 75% would drop to about 71%.

 

[doug293cz]

Borrowing the thread a little if it's ok? , gonna brew a porter with an OG of around 1065 tomorrow, should i adjust for lower efficiency or does that only really appky when you come up to really heavy gravities like 90 and upwards?

Efficiency drop with increasing grain bill size (and target OG) varies continuously. It does not drop off suddenly at some particular OG. The chart below shows how lauter efficiency changes as the grain bill weight to pre-boil volume increased for batch sparging. Fly sparging behaves similarly (but is not amenable to simple a priori prediction.)

Brew on

 

[doug293cz]

Beersmith's estimated mash efficiency is at 75%, wich is what it usually is and it has been correct this far. I'll go with that and adjust it if OG comes out a bit lower than expected.

BeerSmith uses the Brewhouse efficiency that you input to simplistically estimate mash efficiency. The calculation it does is:

Mash Efficiency = Brewhouse Efficiency * Post-Boil Volume / Fermenter Volume​

It does not use your grain bill and strike + sparge volumes to estimate your mash efficiency, which is what it should do.

Brew on