Charring bones for WCP
Can you char the bones on a propane grill for water soluble phosphate?
Top answer
It is possible to burn them on a propane grill. The ideal way is to put them in some sort of column with the heat source at the bottom so they are able to completely char. When the smoke turns clear the process is complete. Remove and extinguish the Bones.
From the KNF library
From the KNF library
Drafted by Claude from Office Hours and the books
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Sep 2026
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7 sources
One Office Hours answer stacks two grill starters, with wood burning in the bottom one and bones in the top one, so flames run straight through and char evenly. (Office Hours Ep. 11, 40:27) Another episode says burning bones directly 'like this' chars them poorly, and that a better method exists. (Office Hours Ep. 107, 46:00) The library does not say what that method is, or whether propane fits.
Drake's checks for done bones:
- Char them black all the way through, not to white ash. (Office Hours Ep. 95, 6:53)
- Brown bones are under-done. Grey bones are over-done. (KNF Demystified, p. 41)
- Finished bones tingle like glass. Unfinished ones thud. (Office Hours Dec 2025, 47:51)
- Char too far and you get potash instead of the form you want. (Office Hours Ep. 136, 30:48)
Use bones from land or water animals. Skip birds. (Cho's Solutions, p. 13)
Sources
- 40:27 Office Hours Ep. 11 (Nov 2021) — Fish Amino Acid vs Hydrolysate, IMO Heat, Seed Soak Storage · “Stack two grill starters, wood burning in the bottom one and bones in the top one, so flames run straight through and char evenly.”
- 30:48 Office Hours Ep. 136 (Aug 2024) — Bone Char, Seawater Minerals, Jadam Leaf Mold · “char it too far to white ash and you just get potash instead”
- 46:00 Office Hours Ep. 107 (Dec 2023) — IMO4 Tea Dosing, Water-Soluble Calcium, Pig Lactobacillus · “Burning bones directly like this chars them poorly”
- 47:51 Office Hours (Dec 2025) — Whitefly Soap Spray, Lemongrass in Pots, Bone Char Calcium · “properly charred bones tingle like glass, unfinished ones thud”
- 6:53 Office Hours Ep. 95 (Oct 2023) — Bone Calcium Phosphate, Juglone Toxicity, Chitosan for Chromium · “you want them charred black all the way through, not white ash”
- p. 13 Cho's Solutions · “Char bones of terrestrial or aquatic animals (not birds!) to a blackened state”
- p. 41 KNF Demystified · “If bones are brown in color, they are under-done and if they are grey in color, they are over-done.”
1 more answer
i would think so propane is a clean burning gas and there would be no more toxins going into the bones then is going into the food cooked on the grill
Also discussed on Office Hours
Desert IMO Collection, Lawn Biochar, WCA Bone Ratios
- 38:35 …fire is charring the bones the second thing that happens is the bones themselves sorry for putting…
- 38:54 …indicates that the um that the charring is done and that now the bones are starting to burn so…
- 39:23 …means that they're no longer charring and the bones themselves will actually light on fire…
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