In the 25 years I have been wood turning I have noticed the interest in wooden kitchen items made from spalted wood has never wavered.
While woodworkers around the world have long marveled at the fascinating colors and patterns that pieces of spalted wood often hold, and while they can be incredibly beautiful, there is a nagging question about how safe the wood is when food contact is involved.
This article is planned to help answer this long asked question so let’s get into it.
Is Spalted Wood Safe For Food Contact?
Yes it can be but there are some details that are worth knowing before jumping into making that kitchen utensil or bowl, and we have them listed below.
- Where spalted wood is likely to be used in food contact.
- How spalting is formed.
- How to tell spalting in wood.
- How spalting can be dangerous.
- How to control the risk when using spalted wood.
- How drying wood can stop it from spreading.
- How spalting weakens wood
- Finishes for food contact with spalted wood.
Where spalted wood is likely to be used in food contact.
Woodworkers are always looking for exotic woods to enhance the asthetics of the product or item they are planning to create, and spalted wood goes a long way to giving a unique figure to any item that is made.
Bowls and kitchen utensils are the primary targets for this kind of wood and this is likely why you are reading this right now. The question of safety is a valid one because there are concerns about the origin of the spalting with that being fungus, and while fungi can be a food for us, it can also be very harmful.
So where does spalting in wooden food contact items fit in? To decide if the item is safe, we need to understand the process of spalting and how it can be harnessed to enhance the beauty of that utensil or bowl without posing any undue risk to the person using that item.
This article should go some way to helping you understand how it all works, from what spalting is, to how a woodworker might handle the risks when making the food contact item, to how the spalting process is stopped and made safe.
You may find cutting boards with spalting, bowls with spalting, carved spoons with spalting, and slab tables also with spalting; the information below is applicable to every single one of them. Even earrings can be made from spalted wood as seen below.
How Spalting Is Formed.
Trees are a major part of the earths natural system and they are made up of many different components like minerals, proteins, acids and chemicals. Wood is the structural component of the tree and as a tree grows it manipulates the surrounding soils to suit its preferred habitat and to form the wood.
Just like every living thing on this planet trees live then die, and the process of being returned to the soil is where spalting comes in.
Example of spalted wood patterns in earrings by Pickers Ridge.
Spalting is the visible evidence of the structural degradation caused by fungus that has entered the wood typically after the tree has died.
It is the conversion of the lignin within the wood into lower form components that are then made available to the next generation of plants.
This process is visible when a block of wood that has been host to the fungus is opened up and seen for the first time.
How To Tell Spalting In Wood.
The evidence that a piece of wood has spalting is purely observational. Each wood has typical colors and grain patterns when the wood is clean, meaning the wood has likely come from a standing healthy tree that was cut down.
Spalted wood most often comes from trees that have already been down for some time, because the fungus needs a little time to perform its artistic magic and it is thought that contact with the ground plays a large part in the process.
When a piece of wood that is clean is placed against a spalted piece the change can be very distinctive, sometimes to an extreme level. The pattern to look for is dark continuous lines of different color tones that don’t resemble the natural color of a typical piece of that particular wood.
It can look like a completely different species in some cases.
How Spalting Can Be Dangerous.
To understand the dangers, you need to consider the way spalted wood is typically used. In the woodwork hobby world, spalted wood is most often associated with wood turning, with some use in the flat board segments of woodwork generally.
It is the conversion of the wood into sawdust where the danger is present because the fungus is a living organism that has natural defenses that can irritate parts of the human system. These defenses that some fungi species possess are chemical in nature and are contained in the sawdust.
Not every wood worker will be affected, and not all fungi have this behavior so it is incumbent on the wood worker to be aware of the potential for danger and to take appropriate steps to contain the risks. Avoid getting this dust into the lungs.
How To Control The Risk When Using Spalted Wood.
As we noted above, the primary risk from spalted wood is in the dust that cutting and processing the wood creates. So it stands to reason that if you were to contain the dust you stand a good chance of containing the risk.
This risk is not just in the dust though but can also be present in larger chips and shavings that a wood turner will generate when performing cuts with turning tools.
Turners often wear a turning smock that protects the turner from shavings and chips becoming lodged inside shirts and such.
It is a good idea to have this level of protection at a minimum for the larger particles generated by turning. As always, a full faceshield should be worn at all times at the lathe.
The dust side of things can be controlled with a full-face respirator helmet if you can afford one and if not, a good particle mask that has a carbon filter incorporated into it will do.
The simple dust mask may not block the chemical components that the fungus contains so be aware of that.
If irritation starts, it is advised to cease turning until better safety equipment can be sourced or don’t play with the wood anymore, depending on the severity of the irritation and the amount of work you have that involves the wood in question.
The risks discussed here are not the only ones to consider and “Is spalted wood dangerous to turn?” covers the others not mentioned here.
Does Drying Wood Stop Spalting From Spreading.
Spalting requires moisture to populate a piece of wood. The moisture level that dictates the end of the life of the fungus involved is not known however the moisture levels for initial inoculation is known to be at least 33% moisture content for some varieties of fungus.
It stands to reason that drying wood to the typical 12% range that wood workers are familiar with should terminate the activities of the fungus. This should not be taken as a complete removal of the dust risk because the chemical residues created by the fungus still remain even after the fungus is dead.
Can you stop wood from spalting?
Yes it is possible to stop the spalting process in wood and it requires a few simple steps. The process needs a good understanding on how the spalting process happens and the environment that is required to allow the spalting to start in the first place.
Once you have that understanding, and you should after this article, the easiest way to stop the spalting process is to remove the wood from the favorable conditions and place it in a position that is the opposite of those conditions.
This means a dry, well ventilated location off the ground where the airflow can move easily. The spalting fungi need moisture and this change in location will dry the wood out and will cause the fungi to become at the least dormant, or possibly/ hopefully kill it.
How Spalting Weakens wood.
Fungi that create spalting are multicellular organisms that feed on cellulose and lignins in wood. These fungi actually feed by performing what could be called backwards digestion.
When we humans eat our food, digestion takes place within our body.
With fungi, they exude secretions into the surrounding wood that breaks down the wood components outside of the fungi’s cellular system then the loaded fluids are drawn back into the fungi’s body, which is usually a thin strand of cells that we call hyphae.
It is this process of digestion that weakens wood to the point of the wood becoming “Punky” and wood workers would be very familiar with that kind of wood. This type of wood lends itself to the resin filled pieces of wood turning that are popular if the punky wood can be stabilized.
A product called cactus juice is used to good effect in this process.
Suggested Finish For Food Contact With Spalted Wood.
Fungi that create the patterns in wood that we call spalting require both moisture and oxygen to continue the process of degradation. When the wood is dried to a moisture content of 12-15% to allow us to work with it, we have removed the moisture component.
To remove the oxygen component we apply a finish to the completed object, be it a slab table, a bowl, a platter, or a utensil. The item is not of concern, the coating is. For a tabletop, the typical coating is a tough long wearing coating that can be a polyurethane, a resin, or a drying oil. The final choice is up to the wood worker and is not applicable here.
For any items that are to be in contact with food, I strongly suggest using pure tung oil.
When applied correctly it penetrates deeply and cures 100% hard and dry.
Several applications of this oil in progressively less-diluted mixes will give a waterproof airtight barrier to your wood that should protect both you and your wooden item for many years.
Spalted wood can deliver spectacular colors and patterns that only a natural process can give. If you are able to find wood that is still structurally sound, and has the hallmarks of fungal staining, you have a treasure chest of natural beauty that will delight for years to come.
The question about spalted wood being safe for food contact is often asked, and we hope we have gone some way to answering the query for you. The bigger question with using spalted wood once the above question has been considered is has the structural integrity of the item been weakened past a point of usefulness.
This will depend on the item as an artistic display piece can carry itself without the issues a bowl or kitchen utensil will have. Over time the woodworker will work out the degree of spalting that can be contained in any particular design.
The final test for the initial question of food contact items and safety is if the item is sound (strong) and it is well coated/finished, then it is very likely to be safe for contact with food. If you still have doubts, then just take a pass on the item and use something else.
References for more research
For an overview of the characteristics of fungi.
Methods on how to inoculate your own logs.
How fungi defend themselves. This is a good read as it explains why and how the separation lines are formed in the spalting patterns.