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Scaling recipe and Est Mash Efficiency

mister2

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I have an equipment profile I have dialed in for 18 gallon batches and a brewhouse efficiency of 81%.  Based on those settings I pretty consistently hit the estimated gravities and volumes that BS calculates for me when brewing batches from 18-25 gallons.  However I recently added a recipe for a much smaller 7 gallon batch based on ingredient percentages (70% pale malt, 10% crystal 20, etc.).  Once I input all the ingredients with the proper percentages using my equipment profile, which has a batch size of 18 gallons, I noticed the estimated mash efficiency is 104%.  The BH efficiency in the recipe is 81% as expected.  My equipment is the same with the usual losses in the chiller, lines, fermenter, etc. regardless of batch size.  I'm just making a smaller batch using those loss volumes.  I'm just concerned with the estimated mash efficiency being >100% and not in the range of 89% that I normally see with other large batches.  Can someone please explain what is going on?  Should I have added the ingredients for the recipe for an 18 gallon batch and then scaled down, or should I have a separate equipment profile for smaller batches and build small recipes using that profile? 
 
Brew house efficiency or total efficiency as BeerSmith uses it is the amount of sugars from the mash that end up in the fermenter.  The program requires some measure of how much sugar is in your process and BeerSmith uses the BHE you specify in your equipment profile to determine the amount of sugar available.  From that value it back calculates the mash efficiency.  When you change the ending amount in the fermenter, but keep the process losses the same, the end result is a lowering of the total efficiency.

I am going to simplify the calculations by using your water volumes as a surrogate for the sugar content.  Your standard process gives you 18 gallons at 81% efficiency.  Your total amount available to you is 18/81% or 22.22 gal.  This means your losses are 22.22 - 18 = 4.22 gallons. 

Now you lower your fermenter volume to 7 gallons with the same system and same process losses.  Your available sugars are now 7 + 4.22 = 11.22 gal.  Your total efficiency is now 7 / 11.22 = 62.4%

Since you left your BHE the same for the 7 gallon batch, the program just assumes that you can draw that much sugar from your mash and inflates the mash efficiency to create that amount of sugar.

edit: for clarity
 
Thanks much for the reply.  I understand why total efficiency is lowered when I decrease the batch size but still keep the same amounts for my losses.  What I can't seem to grasp is the warning I get from BS when I try to scale the recipe from 18 to 7 gallons without changing my equipment profile.  I will always have the same loss amounts in my chiller, brewpot, MT, etc., so it doesn't make sense to alter those, so that only leaves the batch size in my equipment profile.  So I guess that takes me back to my original question - should I have a separate equipment profile for smaller batches, ideally where the batch size in the profile equals that of the recipe I'm wanting to make?  That seems a little inconvenient if I frequently want to make different size batches from time to time.  But hey, whatever it takes to make the numbers add up.  Looks like I need to revisit the docs on scaling recipes.

Thanks again for the feedback.
 
I guess I'm going to accept the idea that even if I normally brew 20-gallon batches and have an equipment profile set for that size and the efficiency accurately predicts my gravities, but I decide to make 7-gallon batches, I will have to create an equipment profile for the smaller batch size and then go through the iterative process of brewing and tweaking my BH efficiency based on measured efficiency in order to get my BHE dialed in for the smaller batch size.  I had hoped the scaling feature could better predict efficiency if the only thing changing was batch volume, but I accept that.
 
Here is the thing to remember, any modeling program for brewing has two material balances it needs to satisfy.  The first is water volumes.  BeerSmith does this by having the user define the volume into the fermenter as well as the process losses.  It can then complete the balance to predict how much water is needed at each step and give you a starting volume to use for mashing and sparging.

The second material balance is a bit more tricky.  This one is for the sugars that make it into the fermenter.  If you just give it a grain bill, there is no way for the program know how much of the potential sugars in that grain bill will make it into the fermenter.  To satisfy the balance, it must have some measure of that value which can be defined either by the mash efficiency or the brew house efficiency.  In writing the model, Brad chose brew house efficiency as his stake in the ground, so to speak, for the sugars that make it to the fermenter.  This is user defined and becomes a fixed variable.  So a 70% BHE means that 70% of the available sugars from the grains/sugars/extract/etc will make it to the fermenter.  It back calculates what the mash efficiency must be for this BHE to be true.

If you change any of the volume input, it directly affects the mash efficiency calculation.  Since the BHE is a fixed variable, it will not change to suit a change in a volume input, such as volume to the fermenter.  Plus there is not way for the program to predict a new efficiency for you, since that is a critical variable which is fixed by the user.

You really should not need to flail about with your efficiency change.  If you take my calculation from the earlier post, it should be fairly close and you would only need to tweak it a little bit to compensate for a change in actual mash efficiency vs BeerSmith's calculated mash efficiency.

 
mister2 said:
I will have to create an equipment profile for the smaller batch size and then go through the iterative process of brewing and tweaking my BH efficiency based on measured efficiency in order to get my BHE dialed in for the smaller batch size.  I had hoped the scaling feature could better predict efficiency if the only thing changing was batch volume, but I accept that.

The quick BHE math to get into the ballpark is to multiply your mash efficiency by the percentage of wort that will get to the fermenter. That should make tweaks for accuracy a lot simpler.

You may find that mash efficiency goes up because of the lower grain bed depth, or down if you have unrecoverable dead space. As Oginme said, it's all about the percentage of total sugar that gets to the fermenter.
 
Thanks, guys, for your feedback.  What you're saying makes sense and I'll apply that knowledge to the creation and maintenance of individual equipment profiles that have BHE and batch sizes that match the amount of beer I'm making.

My understanding of the equipment profile was too focused on a description of the hardware and losses only since those are mostly static.  I was always puzzled by the warning about scaling a recipe without changing the other variables in the profile but now I have a better understanding behind that warning.  I may be the only person that struggled with this, but it might be nice if the warning message says something along the line of 'You might want to adjust the batch size and BHE setting in the equipment profile since I see they don't match your recipe batch size (or choose a different profile that does match).
 
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