BeerSmith mash / lauter tun deadspace and the effect on gravity?

[thehopbandit]

In regards to mash/lauter tun deadspace in BeerSmith, I have a couple questions.

Assume a recipe with 12 lbs of malt, batch sparging. I have been messing around with the tun deadspace box to see how it affects the calculations. I am very confused, however, because BS doesn't seem to be calculating anything different other than water volume used.

Assuming constant other variables between these two situations, look at the following:

Deadspace setting at 0 gallons:
Mash water: 4.5 gallons
Sparge water: 4.42 gallons
Pre-boil: 7.48 gallons (8.92 gallons total water - 1.44 gallons grain absorption - 0 gallons of deadspace)
OG: 1.060

Deadspace setting at 1 gallon:
Mash water: 4.5 gallons
Sparge water: 5.42 gallons
Pre-boil: 7.48 gallons (9.92 gallons total water - 1.44 gallons grain absorption - 1 gallon of deadspace)
OG: 1.060

I'm confused here. Wouldn't accounting for the deadspace (i.e. adding an additional gallon of water to the mash/sparge that gets left behind) further "dilute" the dissolved sugars, making the OG less overall? According to BeerSmith, the only change that happens when accounting for the deadspace is that you just add an additional gallon of sparge water to make up for the one gallon that gets left behinds.

In the first example, the only water lost is water absorbed by the grains. In the second example, you have water absorbed by the grain but also 1 gallon of water (that has mixed sugars in) that is going to stay behind. In essence, both examples have the same, constant amount of sugar available. You are producing 8.5 gallons of pre-boil wort (1g is left behind as deadspace) in the second example and 7.5 gallons in the first. Surely the OG's would be different?

With a constant amount of sugar that presumably dissolves evenly, it doesn't seem possible that the OG's would be the same. If it were, then it would mean you could (theoretically) have a tun with 10 gallons of deadspace and the OG wouldn't change?

To illustrate another way. With the deadspace at 0 gallons, we are dissolving the sugars from 12 lbs of malt into ~8.92 gallons of water. With the deadspace at 1 gallon, we are dissolving the sugars from 12 lbs of malt into ~9.92 gallons of water. Why would BeerSmith calculate the OG as the same in both situations?

 

[Oginme]

BeerSmith works by setting the overall or Brewhouse efficiency as a fixed variable. When you change the amount of water, as in your example above, BeerSmith adjusts the Mash Efficiency to compensate to keep the Brewhouse efficiency at the set target.

 

[thehopbandit]

BeerSmith works by setting the overall or Brewhouse efficiency as a fixed variable. When you change the amount of water, as in your example above, BeerSmith adjusts the Mash Efficiency to compensate to keep the Brewhouse efficiency at the set target.

Thanks for the reply. However, the Est Mash Eff number is the same between both examples.

 

[brewfun]

Wouldn't accounting for the deadspace (i.e. adding an additional gallon of water to the mash/sparge that gets left behind) further "dilute" the dissolved sugars, making the OG less overall?

Yes on dilution. Maybe on lower gravity.

According to BeerSmith, the only change that happens when accounting for the deadspace is that you just add an additional gallon of sparge water to make up for the one gallon that gets left behinds.

Functionally, you'll still see the same final runnings gravity and deadspace gravity. The only thing diluting is the final gravity, not the total runnings because the deadspace represents the same gravity as whenever you're measuring during the sparge.

In the first example, the only water lost is water absorbed by the grains.

Red herring. The water trapped in the grain is the same gravity as the surrounding water because osmosis drives extraction. You know this because of what follows.

In the second example, you have water absorbed by the grain but also 1 gallon of water (that has mixed sugars in) that is going to stay behind. In essence, both examples have the same, constant amount of sugar available. You are producing 8.5 gallons of pre-boil wort (1g is left behind as deadspace) in the second example and 7.5 gallons in the first. Surely the OG's would be different?

OK, here is where you start to misunderstand the dynamics of your last runnings. If you go all the way to 1.008 as your final runnings and allow that to run for 1 gallon, the deadspace is at the same gravity. So, the total sugar loss from deadspace is 8 points (because without deadspace that last gallon would be 1.016) divided across your entire preboil volume. in a 7.5 gallon preboil, this is about 1.001 additional gravity.

Functionally, this is less than the resolution of the most common hydrometers and refractometers. I think you have to run your mash efficiency out to 4 decimal places to see this value.

With a constant amount of sugar that presumably dissolves evenly, it doesn't seem possible that the OG's would be the same. If it were, then it would mean you could (theoretically) have a tun with 10 gallons of deadspace and the OG wouldn't change?

Interesting supposition without a practical application, since the deadspace would represent 134% of your preboil volume. Though if calculated as 1.008 end runnings, it would have an impact. In fact your mash efficiency might be close to zero.

But, the point Oginme made about Brewhouse efficiency is the main factor in why BeerSmith is showing you certain numbers. This efficiency is not the same as mash. Brewhouse Efficiency is a statement of the percentage of total sugar available you expect to get to the fermenter. You can make it innacurate, if you wish. However, if you say you are getting 80% of the sugar into the fermenter, and add to accumulated deadspace, the ONLY place where this can come from is increased extraction from the grain. So, if improperly used, mash efficiency will be calculated at over 100% extraction.

This is why your deadspace additions don't change gravity. Nor will additions to Trub Loss. BeerSmith is doing exactly what you tell it by calculating the total percentage of sugar going into the fermenter and increasing mash efficiency to find it.

 

[pricelessbrewing]

Beersmith does not calculate efficiencies, all the gravity readings are calculated based on your input efficiency.

As far as I know, my mash software is really the only one that will estimate all of your efficiencies (and therefore gravity readings) based on recipe, equipment, and process.

 

[thehopbandit]

Thank you for your replies. I understand the concepts behind what was said, but have a couple followups.

Yes on dilution. Maybe on lower gravity.
OK, here is where you start to misunderstand the dynamics of your last runnings. If you go all the way to 1.008 as your final runnings and allow that to run for 1 gallon, the deadspace is at the same gravity. So, the total sugar loss from deadspace is 8 points (because without deadspace that last gallon would be 1.016) divided across your entire preboil volume. in a 7.5 gallon preboil, this is about 1.001 additional gravity.

Is this notion the same for batch sparging? Apologies for my ignorance, but to me, in an over simplified example, compare a tun where you add 5 gallons of sparge water and drain out all 5 gallons versus a tun that has a gallon of deadspace (add 6 gallons to get 5 gallons). If you have a constant amount of sugar dissolved in 5 gallons of 1.020 wort and then presumably add an "extra" gallon of water to that (deadspace), you end up with 6 gallons of 1.017 (5 of which will make it out of the tun), which is a small but non-negligible difference.

 

[brewfun]

Is this notion the same for batch sparging?

Of course.

If you have a constant amount of sugar dissolved in 5 gallons of 1.020 wort and then presumably add an "extra" gallon of water to that (deadspace), you end up with 6 gallons of 1.017 (5 of which will make it out of the tun), which is a small but non-negligible difference.

Well, there are multiple answers, here.

• If we're talking technique, then another batch is warranted at that gravity. A second sparge can make a 4 to 6% increase.
• If we're talking gravity resolution in wort, then it's enough to make a 1.002 impact on the starting volume of 7.5 gallons in your original post.
• If we're discussing a system design and this loss is a concern, then a modification to recover the 12% volume loss is warranted.

In all of those cases, we're discussing mash efficiency. However, we were discussing how BeerSmith calculates and that is based on Brewhouse Efficiency, which circumvents the rest of the calculations because it accounts for losses at every stage and is very easy to measure. Just the gravity and volume in the fermenter vs the total potential of sugars. When you put in your measured values, it's then that you see the real difference between estimated and actual mash efficiency.