[BUG] Pre-boil gravity calc in recipie builder

aboman

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It looks like the recipe builder is using the wrong value when calculating pre-boil gravity and consistently is lower than it should be.

I believe it uses Batch Size and Boil Size without pulling in kettle loss volume from the equipment profile (kettle loss number needs to be added to the final volume before doing the dilution calc for pre-boil gravity).
 
Thanks for the feedback - I'll look into this. When you're looking at those calculations are you looking at the recipe itself or a brew session? As I understand it, the recipe itself doesn't included any of the information from the equipment profile, while the brew session is able to use the equipment profile to predict values more accurately based on that configuration information.
 
I'm looking in the recipe, not the session.
 
Hmm, careful here. Did you really mean kettle loss for pre-boil gravity? You don't lose anything in the kettle at that point. Did you mean mash tun loss? Kettle loss is only post-boil, when you leave trub behind on the way to your fermenter.

Also, whether you drain every drop into your kettle from the mash tun, or only enough to fill a hydrometer tube, the gravity is the same. So I'm not sure what the issue is here regarding loss at the pre-boil point affecting estimated gravity.

I have raised another bug about post-boil cooling shrinkage not being taken into account; it's not listed in the Quick Water Calc nor is it considered in the ending kettle efficiency value. But I have somewhat exhaustively recreated water volume and gravity equations in a spreadsheet, and Brewer's Friend and I are in sync with pre-boil gravity.
 
It is an algorithmic thing with how I think they come up with the pre-boil gravity estimate using OG, Boil size and Batch size. It doesn't have anything to do with actual brewing steps.

For the current beer I'm editing the pre-boil should be 1.070(ish), but it is estimated to 1.060 in Brewers friend. The current equipment profile has almost a gallon loss in kettle that needs to be accounted for that is why the difference is so high in this case. That assumes the algo works as I suspect, if I'm wrong about that then the algo is wrong somewhere else.

It looks like that number is the same (also wrong) in the brew session as well, at least up in the header.
 
Again, I'm not sure we're on the same page.

Pre-boil gravity doesn't get affected by any losses. Only efficiency does, because it's a combination of gravity and volume. When you mash, you extract sugars from the grain. After the mash, whether you take a gravity sample directly out of the mash tun, or out of the kettle after lautering (before boiling), the gravity reading will be the same.

Only after you start boiling, which evaporates water and further concentrates the sugars in the wort, does the gravity change.

Does this clarify or are you referring to something else altogether?
 
We are not on the same page.

I'm not talking about the actual brewing process. I'm only talking about how I believe, from quickly checking some numbers, the software calculates the (rough) pre-boil estimate when you target fermenter. Not about actual losses or efficiency.

To expand:
It looks like the calculation uses the same stuff as here:
http://www.brewersfriend.com/dilution-a ... alculator/

From that they need starting and ending volumes along with gravity to estimate the pre-boil gravity. If they do that calculation using the other numbers they have there, namely: pre-boil volume, ending volume (in fermenter) and estimated ending gravity the pre-boil gravity will be off since your volume will be off with however much is left in the kettle. The ending kettle volume needs to be used instead, thus if they pull the kettle loss value from the equipment profile they can get an estimate that is much better.

Consider these rounded numbers (plug them into dilution & boil off calculator):
1.080 gravity (post boil, from recipe, grain, efficiency etc.)
7.5 gallon pre-boil volume.
5.5 gallon targeted in fermenter.
1 gallon/hour boil off.
1 gallon kettle loss.

Brewersfriend will currently estimate the pre-boil gravity to 1.060, that is off by 0.010 points in this scenario.

If you switch the target to be kettle, and enter mash efficiency instead of brewhouse then the number will be correct because of how they do the calculation.
 
I don't think this is a bug - more of an unimplemented feature. There's a post from back in 2013 (viewtopic.php?f=5&t=824) where Larry explains that boil gravity doesn't take the equipment profile into account ie. it doesn't account for losses.

I find it easier to do all calcs into the kettle (rather than the fermentor) and work out manually how many points I need preboil.
 
Right.

The thing about using kettle volume is that you have to fiddle with it and check the water calculation to hit your intended volume etc.

I know how to do these things and how to get the right numbers manually, I just think that the software should present the right number if it is to show anything at all. At this point if you don't know about the issue and you try to hit the number as shown during fly sparging (for example) your OG will be off, perhaps significantly.

The 'fix' is also trivial, and should take about 30 seconds to make.
 
I agree that the change sounds simple, but Larry didn't think so, and he ...

a) knew the system very well, and
b) was very active in improving it.

Most of the changes that have been made since Larry left have come with unintended side effects (aka bugs). Rather than requesting new features I would encourage the new administrators to concentrate on not breaking anything else. I certainly wouldn't ask them to attempt something that Larry thought was tricky.

The reason I target the kettle is because my kettle losses (primarily break material and hop adsorption) are the least predictable part of the process. I usually set out to brew 28 litres into the kettle which generally will turn into about 25 litres into the fermentor. However, hitting the intended OG and hop profile is much more important to me than exactly how much wort I collect.
 

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