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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.
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.