Baking Eggshells for WSC
Howdy All,
I've been collecting lots and lots of eggshells for WSC. Too many to fit in a pan (neighbors have been loading me up on their eggshells). Would it work if I crush them up and put them in the oven at 180 for about 2 hours?
Thanks.
Binyamin
Galil Soil Farm
The answer
Yes, the oven will work well. 180 for 2 hours seems appropriate to get rid of the moisture. I think it will have to be a bit warmer to toast out the organic material. Seems to me more like 250 for 2 hours, but this is an energy thing. Don't want to burn them, and I don't have any empirical evidence on this as I always use the pan method, but I typically use a low medium heat, which is a bit more than what the textbook calls for, but we did this in Korea under Master Cho's watch and he nodded in approval of the higher heat, quicker cook time.
When baking in the oven, crushing is not necessary unless it makes sense. When cooking in the pan, crushing is mandatory trying to get the shells 1-2mm in size. I do not recommend powdering them.
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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4 sources
Drake recommends judging by doneness, not the clock. Cook the shells brown like a marshmallow on relatively low heat. (Pure KNF Manual, p. 51) That evaporates residual water and bakes out the organic matter. (Pure KNF Manual, p. 51)
The library's times are for a pan, not an oven:
- Cho's recipe says about 30 to 40 minutes, varying by season. (Cho, Recipe, p. 60)
- Another recipe crushes shells to about 3mm and cooks 45 minutes on low heat, cool enough to touch. (Cho's Solutions, p. 13)
Both sources say finished shells turn much lighter in weight. (Cho, Recipe, p. 60) (KNF Demystified, p. 40) They split on color: one says the shells brown, the other says brighter than the original. (KNF Demystified, p. 40) (Cho, Recipe, p. 60)
Once cooked, add the shells to 10 times their amount of vinegar by weight. Let them dissolve until the bubbling stops. (KNF Demystified, p. 40)
The library gives no oven temperature or oven time.
Sources
- p. 60 Cho, Recipe · “Lightly roasted shells show a brighter color than the original, and become very light in weight. It takes about 30~40 minutes to roast, even though it varies depending upon the seasons.”
- p. 40 KNF Demystified · “The shells will brown in color and become lighter by weight when cooked completely. Add cooked shells to 10x of vinegar by weight and volume Allow to dissolve for several days until the eggshells stop bubbling.”
- p. 13 Cho's Solutions · “Crush eggshells to ~3mm pieces • Cook eggshells on low heat (your hand should be able to touch the eggshells while cooking) for 45 minutes”
- p. 51 Pure KNF Manual · “cooked brown like a marshmallow on relatively low heat in order to evaporate out any residual water inside the material as well as baking out the organic matter”
