Author Topic: Possible Bug  (Read 4645 times)

msavage4

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Possible Bug
« on: November 18, 2008, 04:24:15 PM »
This was posted in another forum but got no response:

"It seems the OG calculation is only related to grist bill & "Batch Size" field. Nothing else changes it. This is a problem. I'll give a simple example. Lets say I want to collect 5 gallons of 1.040 wort into my fermentor. One would think that I should set my batch size to 5 gallons and add grains to hit 1.040 based on my brewhouse efficiency. But I also need to keep in mind the amount of water needed and wort lost elsewhere in the process. BS provides a handy tool to calculate and keep track of all these issues, boil-off, deadspace, etc. My kettle holds about .75 gal of lost wort in the trub and dead space. If I set this value to .75 in Beersmith it correctly back-calculates the water needed at the start of the boil. HOWEVER it does not change the OG to reflect the fact that I am now brewing 5.75 gallons of wort! A simple experiment will show this and why it is wrong. Go into BS and set the "Lost to Boil Trub & Chiller" value to 10 gallons. You are now making 15 gallons of beer with the same amount of grain yet the OG does not change! In my set up I really do need to end up with 5.75 gallons of wort to get 5 gallons into the fermentor. Of course I can just change the batch size to 5.75 gallons and set the trub/chiller loss to 0 and get the right OG but that is counterintuitive and makes the trub/chiller loss field useless. There are other fields that behave in the same way. Of course the efficiency calcs are completely wrong in all cases because they take none of these losses into effect. Am I missing something here?"

Offline BeerSmith

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Re: Possible Bug
« Reply #1 on: November 18, 2008, 06:23:25 PM »
Hi,
  The brewhouse efficiency (by definition) includes the losses you describe - it is the "gross" efficiency for your brewing system.  An alternative would be to use the MASH efficiency and then calculate forward from there (using trub loss, boil loss, etc...) to get the final OG.

  Most brewers use brewhouse rather than mash efficiency when formulating recipes, which is also what BeerSmith does.  I'm considering adding an option to allow calculating from mash efficiency instead for a future version.

  Here's more on the topic including how to calculate it by hand:
   http://www.beersmith.com/blog/2008/10/26/brewhouse-efficiency-for-all-grain-beer-brewing/

Cheers,
Brad
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Offline MaltLicker

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Re: Possible Bug
« Reply #2 on: November 19, 2008, 07:59:40 AM »
I was able to duplicate your findings and I see what you mean; however, I think the problem lies in what BSmith is designed to do.  Instead of deadspace loss, think of spilling a gallon on the floor.  BSmith cannot predict that size loss after you've entered a prediction of spilling only 8 ounces.  Once you tell it that you spilled a gallon, it can tell you you'd better use more grains and water next time (if you want to fill the carboy.) 

BSmith is designed to take the specs and conditions that you have documented on your equipment in the past, and it then does the grunt work math for us, for future batches.  Equipment Profile settings do not appear to be interactive like EE% and Batch Size.  (Perhaps logically, because it is hard to imagine that the deadspace lost would suddenly increase from 0.75 gallons to 2.0 gallons during a brew.)  If it somehow did, then you'd click on "Brewhouse Efficiency" and enter a new Actual Batch Volume of 4.50 gallons, reflecting the additional loss of 1.25 gals.  BSmith reflects this as a 16% decrease in efficiency (down to 59% instead of the 75% I used), because it believes the deadspace to be 0.75 gals.  IF this condition was expected to persist, then you'd either enter a 2.0 gallon loss in your equipment profile, or you'd enter a 59% efficiency for the next batch and use more grain.  Or change your batch volume to 4.50 gals.  Either way you have to tell BSmith what to expect and then run with that thru the entire process.  (Software-wise, that may be why the equipment choice is made before any ingredients are selected.)   

Also a good example of why it is vital to measure all the key stats on each brewing rig in order to get meaningful forecasts from BSmith.  All the losses, the evap rate, the batch size, etc., are believed to be correct by BSmith when it calculates OG and everything else. 

katzke

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Re: Possible Bug
« Reply #3 on: November 20, 2008, 11:02:51 AM »
I see this as a problem also. One reason to use a program is to get automatic calculations.

If my equipment changes then my recipes should change also.

This may be related to similar complaints I have read about how IBU's are calculated.

If I want 5 gallons of wort in the fermenter and know I loss a gallon in the system then I am really making 6 gallons of wort.  If this change is made in the equipment nothing in the recipe changes.  In fact I just found that a change I made in my equipment does not show up in the equipment profile in the recipe.  I changed the hop utilization % and in the recipe it is the old value when I look at the equipment profile in the recipe.

As it is I can not use the program to calculate my boil volume because I can not adjust the grain absorption.  Now I find that the estimate of gravity is not correct for my system settings because the program does not calculate the wort volume correctly. 
« Last Edit: November 20, 2008, 02:57:56 PM by katzke »

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Re: Possible Bug
« Reply #4 on: November 20, 2008, 07:16:09 PM »
Well,
  I see your point, and appreciate it.  By convention, brewhouse efficiency is used in exactly the way I describe by brewers around the world to account for ALL losses in the brewing process.

  As I mentioned I'm looking at adding an alternative system based on mash efficiency and equipment losses for a future version so you will have the option of using either method.

  As for the equipment profile - a copy is stored in each recipe (since in most cases you would like your equipment settings to go with the recipes as you pass them around.)  Therefore changing the central equipment profile does not automatically change all recipe profiles.  This was done quite intentionally since people are often changing equipment or bringing in recipes from friends that might have different equipment settings.  You can adjust to a new set of equipment using the scale recipe command.

Cheers,
Brad
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katzke

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Re: Possible Bug
« Reply #5 on: November 20, 2008, 07:35:00 PM »
Are we even talking the same thing?

You say you account for all losses.  But when we add more losses to trub the wort volume should increase and the efficiency decrease for a given final volume.  Only if the final volume decreased would the efficiency stay the same.  We are loosing sugar in the process and I do not see how you show that when the expected gravity stays the same.

Same with hops and IBU calculations.  If I start to boil with 8.5 gallons and leave 1 gallon behind for trub and kettle loss then end up with 5 gallons in the fermenter I really brewed 6 gallons not 5.

As to the equipment thing.  Any way to have an update to all the recipes or selected recipes or something?  It would be a real pain to have to go in and change all the recipes just because Santa brought a new boil kettle or mash tun.

 

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