water proof and food safe finishing for a wooden bread bin

Question

I have a wooden bread bin, with the bottom (floor) bit being a 3.6mm plywood. The rest of the build is solid wood, 12mm thickness. The bin was dropped at one point and the bottom of it cracked; the moisture got in and mould started growing on it.

I decided to replace the bottom altogether and got the same thickness plywood - to make sure it fits into the slots on the sides, front and back. However the question is how to finish it - to make sure it's both water proof and food safe, after all, bread would be resting on it most of the time.

I did consider options such as linseed oil or even olive oil, but those may not be durable enough and (at least in olive oil case) have some odour, which wouldn't be great in a small enclosed bread bin. Ideally, I'd like a film-like finish for protection, but a normal wood stain isn't food safe.

So, what's the best finish for the bottom of the bread bin?

P.S. I'm in the UK if it matters.

Answer 1

Summary of non-toxic finishing products for wooden bowls and wood cutting boards:

Mineral oil: derived from petroleum, it is colorless, odorless, tasteless and entirely inert. Simple to apply, low water resistance, frequent reapplication. Highly processed variants are food safe and labelled as such. Do not confuse with mineral oils used as machine oil.

Beeswax: The work of the honey bee, extracted from frames in a bee hive. Best applied when heated. Ask your local beekeeper.

Shellac. A secretion from the lac bug. A film-forming finish, which is easy to wipe and clean with a moist cloth. Use high-purity denatured alcohol as a solvent, as it leaves no toxic residue.

Raw linseed oil: Pressed from flax seeds. Very long curing time, good looks, low water-resistance, frequent reapplication. FOr shorter drying time use polymerized linseed oil which is still food safe, but not "boiled" linseed oil. Rags may self-combust.

Pure tung oil:, from the nut of the china wood tree. Difficult to apply, requires many coats, good water-resistance.

Walnut oil: Pressed from the nuts of the walnut tree. Dries and won't go rancid. Easy to apply, frequent reapplication.

Carnauba wax: Derived from the Brazilian palm tree. Straight on woodenware as a light protective coating or a topcoat polish.

The above is abridged, reordered to my preference, and mildly edited, from https://www.newhampshirebowlandboard.com/blogs/blog/13612445-food-safe-finishes-for-wooden-bowls-and-wood-cutting-boards

More on the variants of linseed oils:

• Raw Linseed Oil is the purest, most natural form of the oil. It is the kind used in nutritional supplements
• Polymerized Linseed Oil is created by heating raw linseed oil in the absence of oxygen to about 300°C (572°F) over the course of several days.
• Boiled Linseed Oil has drying agents (either petroleum-based or heavy metals) added. It is the least food-safe of the three.

Ref: https://vermontwoodsstudios.com/blog/raw-vs-boiled-vs-polymerized-linseed-oil/

More on tung vs linseed oil: https://woodworkingtoolkit.com/tung-oil-vs-linseed-oil/

Self-Combustion of Oily Rags

The reader should be cautioned about the storage of oily rags:

The entire combustion process of the samples includes 4 typical stages: low-temperature oxidation stage, thermal decomposition stage, combustion stage, and after-combustion stage. The activation energy of the low-temperature oxidation stage reached as low as 33.13 kJ/mol, indicating that the vegetable oil is extremely prone to self-oxidation even when the temperature <200 °C. And the self-ignition tendency was in the order linseed oil > perilla seed oil > safflower seed oil The continuous oxidation and self-heating of vegetable oils in the air can result in the occurrence of fire due to thermal runaway via heat accumulation. This is especially true when the unsaturated vegetable oil is immersed in a carrier such as cotton cloth or fiber, as the much larger contact area between O2 and oil results in an oxidation rate and thereby increases the risk of fire. If there is sufficient accumulation in the carrier, the heat released by the reaction can easily accumulate due to the overlay effect of the accumulation. Once the ignition temperature is reached, the oil will burn in the presence of O2.

https://www.sciencedirect.com/science/article/abs/pii/S0360544221031364

Answer 2

Clear shellac or mineral oil are your best choices.

Answer 3

I use mineral oil on anything that needs to be food safe; there are also some commercial oils/waxes that can be used (butcher block oil is the most common I can think of).

Alternatively, you could get a baking/sheet pan that fits inside to rest the bread on/in. This has the added benefit of removing it to clean and empty crumbs that might have broken off the bread.

Also, keep in mind that the bread is far more moist than the air and mold is more a factor of the cracked base allowing mold spores easier access and not a factor of the wood being air permeable.

Answer 4

Bread bins are not meant to be used in moist environment. Bare wood is perfectly fine in this use scenario. If your bread box experienced conditions enabling mould to grow then the bread inside would also grow it.

Mouldproofing the box alone won't do you any good. You need to dry up the environment.

Answer 5

Whatever you do, don't use olive oil. It'll go bad and smell nasty.

We could spend months talking about various wood finishes, but for something like this you should just keep it simple.

Water-based polyurethane is the quickest and easiest way to finish wood. It's available at any hardware store (at least here in the US). It dries quickly; leaves a smooth, durable, water-resistant surface that's easy to clean; and unlike many other finishes, it doesn't give off nasty fumes while it's drying.

Put on the first coat, let it dry. You'll probably notice that the surface became rougher than it was before; don't worry, that's normal. Sand it lightly with fine paper (220 or so), wipe off the dust. Put on a second coat. Done. (You can do a third or fourth coat if it's a high-wear surface like a tabletop, but this won't be necessary here.)