Shrinkage! Costanza's Efficiency Bug

[McKnuckle]

This has had me pulling hair for weeks and I think I've found the culprit. I did a bunch of research, comparison with BeerSmith, and spreadsheet geekery to track this down.

There's a parameter for post-boil shrinkage due to cooling in the equipment profile; this is typically set to 4%. However, the value is not used in either the water volume or efficiency calculations.

This is particularly an issue for efficiency. The "Ending Kettle" value displayed on the recipe is actually reflecting the Pre-Boil efficiency instead. It should always be lower than Pre-Boil, because while the gravity/volume ratio is in proportion at both stages before cooling, it is not so after cooling. Ending Kettle efficiency will always be lower due to the "shrunk" volume which changes the ratio and lowers the PPG value.

And while you're at it, might as well incorporate shrinkage into the Water Requirements function on recipes and brew sessions. It should be inserted as an additional loss just before trub loss (multiply post-boil volume by 1 - ShrinkPercentage to get the final, cooled ending kettle volume).

Here's what the FAQ says for Ending Kettle:
Brew Log Type - 'Boil Complete'.
Gravity - OG, measured after cooling, before pitching yeast.
Volume - ending kettle volume when cooled, before draining.
Kettle dead space, trub losses, and hops absorption do NOT count against this measure.

If this is too technical I suggest reaching out to Larry for his review if he's still accessible.

 

[McKnuckle]

Just to follow up and assist in your research:

The Quick Water Requirements window states that values are calibrated to 68F. But that doesn't really make sense, because there is no compensation for wort shrinkage in any of the figures. If the values were calibrated, you'd have the volumes that represent hot liquor be adjusted down according to the shrinkage percentage. But they are not. And furthermore, changing the shrinkage percentage in the Equipment Profile has no effect on the Quick Water Requirements. I even tried 10% - a value that should have an obvious effect - but all volumes were the same as when the percentage was set to 4%, and the math only takes the usual physical losses into account (absorption, evaporation, etc.).

In contrast, BeerSmith has a discrete field for the volume lost to shrinkage on its "Vols" tab in a recipe, and the volume reaching the fermenter reflects it.

 

[Ozarks Mountain Brewery]

in the recipe in edit mode did you pick the correct profile save it the view again and if its a brew you need to edit the brew then save or update, I think there was an issue I had once before too but not sure it was resolved by editing saving , closing and reopening

 

[McKnuckle]

I definitely have the correct profile selected, and in any case, all of my profiles include a shrinkage element. It doesn't work. I edit, save, and view repeatedly while working on recipes and the shrinkage is never incorporated into the water requirements. Tracking down the efficiency impact was much more tricky, but it is missing from that as well. It results in the "Ending Kettle" efficiency being over-estimated by 3 or 4 percentage points.

 

[McKnuckle]

Any comment from Austin or Josh...?

 

[Josh (Brewer's Friend)]

Sorry for the delay; just had a chance to read through your notes on this. Thanks very much for spending the time to figure this out. To be honest, I haven't touched this portion of the codebase yet, so I'll need to spend some time figuring out how the code for these calculations works. I'll start looking into this and will follow up when I figure out what's going wrong.

 

[McKnuckle]

Thanks - and feel free to PM/email if you want further clarification. I have a nice spreadsheet that shows the discrepancy I believe I'm seeing.

 

[McKnuckle]

Over a year later, and I notice that shrinkage is still not incorporated into the "quick" water volume popup on recipes.

 

[Brewer #77071]

Over a year later, and I notice that shrinkage is still not incorporated into the "quick" water volume popup on recipes.

Corrrect me if i'm wrong but water volumes are measured at room temp so will expand when boiled but then shrink back on cooling. So no net effect????