How do I remove mold from an old oak barrel?

Bleach, leave in Sun, spray down with Lysol mold killer.

Vinegar is your best bet. Vinegar will kill the mold spores. Bleach does not.

https://www.servicemaster-restoration-cleaning.com/2017/03/30/mold-myths/

https://www.servicemasterrestore.com/blog/mold-damage/mold-myths-will-vinegar-kill-mold/

https://restorationmasterfinder.com/restoration/what-kills-mold-bleach-vs-vinegar/

You need to saturate the affected areas and let dry thoroughly. Then have at it! Will be great decor anywhere you want to use it.

Thanks so much for the answers!!

TSP Trisodium phosphate!

Take a 1 gallon container and fill it with hot tap water. Add about a cup to 1 1/2 cups of tsp and stir. Be sure to wear gloves and a mask while doing all of this.

I use very hot water in order to open up the wood grain and draw out any stains.

You need to do this in a space where it won't seep into the soil. A cement garage floor would be ideal. Just be ready with a mop.

Pour the mixture all over the barrel. Take a tooth brush and scrub the moldy areas just to open up the grain a little more. Pour a little more over these areas again. Leave it to dry. It should give you a uniform color all over the barrel. I've used this method in the past when refinishing furniture. It acts as a bleach and takes out many stubborn stains. I've also used it to even out the color on an old parkay floor. You leave it to soak in and dry on it's own. The floor 40 year old floor looked almost new again. This is also a great method to use when stripping furniture as it removes all the stripper residue and evens out the wood surface tones at the same time.

TSP is a natural substance but is caustic just as bleach is.

Hope this helps....

More info here:

https://shadowproof.com/2012/12/09/cheap-effective-mold-removal/