I read because your tub is planed, it does not need sealants or any chemical product. If soy sauce gets spilled on it and left to dry, would it stain or can be simply wiped off?
About the finishing, we offer 2 options:
1) simply planed: in this case you have to wash away immediately any spill or it will stain. If you get a stain, blot wisely with some bleach and rinse promptly until the stain is removed.
2) treated with “kihada ichiban”. This product is a hydrorepellent which does not create a film on the wood. It is very safe and environmental friendly but it is a chemical product.
Please find more info here:
In this case the spill will not penetrate the wood. The manufacturer warns that the hydrorepellent effect might diminuish after 2-3 years but in our experience we could not find considerable performance loss.