Is Anodising Food Safe?
We are often asked at Metal Finishings Ltd about whether anodising is food safe. The short answer is: it depends, and the long answer is below.
There are various types of anodising, there are two varieties that can be made food-safe (this does not mean they are always/automatically food-safe):
The other varieties use substances that are harmful even at low concentrations and so are not sensible choices.
This answer discusses sulphuric acid anodising and hard anodising with sulphuric acid and further references to anodising in this article should be read as limited to those types.
Anodising forms a layer of aluminium oxide on the surface of aluminium. This is useful because it inhibits corrosive attack of the aluminium underneath. It also increases the hardness of the surface, which is useful for scratch resistance.
Some people are concerned about the health effects of aluminium. The health effects of aluminium are outside the scope of this article, but our view is that the evidence of harm from typical exposure is weak. Nonetheless, because the coating of aluminium hydroxide reduces attack of the aluminium, it should reduce exposure. Aluminium oxide is insoluble, except in acidic or alkaline conditions. The relatively short contact of aluminium oxide coatings with slightly acidic foodstuffs that may occur in normal cooking usage is unlikely to be problematic either.
Anodised aluminium is widely used as a treatment for cookware, food contact surfaces and food processing equipment. So there is a strong precedent for using it as a food safe material. Aluminium and various aluminium compounds have been allocated E numbers.
What needs to be done to ensure food safety?
As stated above, not all forms of anodising are food safe. To be sure of a food-safe surface, you should require the following:
- The part must be made out of food-safe aluminium
- The part must be sulphuric anodised or hard anodised, using only sulphuric acid in the anodising electrolyte
- The part must be sealed only in pure, de-ionised water (boiling water seal)
- The part must be rinsed at the end of the process in clean, de-ionised water
The object must be made out of a suitable grade of aluminium. Suitable grades of aluminium for use in contact with food are given in BS EN 601 and BS EN 602.
Hard anodising will be more suitable than sulphuric anodising for surfaces liable to wear (true of most cookware).
It is important that sealing is accomplished in pure, de-ionised water only. Other sealing options contain substances that are not food safe. For the avoidance of doubt, sealing with nickel compounds (such as “cold sealing”) is not safe for food contact in our opinion.
Unsealed coatings are liable to corrosive attack, may be unhygienic and should be avoided.
You should ensure that the anodising company acknowledges these details in writing for each batch (usually by stating them on their certificate of conformity).
Coatings that are dyed (not the natural colour of the anodising) are unlikely to be food safe and you should assume they are not safe unless you are shown evidence that shows otherwise. With dyed coatings, there may also be concerns about how the dye will behave when heated during cooking. Metal Finishings Ltd do not recommend dyed coatings for food-safe applications.
Further guidance about food-safe anodising is given in BS EN 14392.
For ease of cleaning, non-stick properties and to further prolong the life of the part and its surface, you may wish to have the anodised surface coated with a suitable polymer coating. These will often have product-specific food-safe approvals.
End users of the product should be given instructions about how to care for the anodised surface, we suggest:
- Wash before first use
- Clean with non-scratch scourers/sponges
- Clean with mild cleaning solutions (such as washing up liquid), avoiding acidic or alkaline cleaning solutions
- Do not thermally shock (for example, do not heat up and plunge into cold water)
- Use only non-scratch utensils
This article is intended as a primer to anodising and food safety. Your use of any material or process should be considered in you safety assessment and product design process.
This page is provided for information only, it should not be considered advice and we cannot accept any responsibility or liability for your use of the information on this page. The information on this page is used and relied on at your own risk and you bear the sole responsibility for any outcomes. E&OE.