The most common question we get on our Facebook forum and sometimes on this website for Beer Can Cleaning is how to use oxalic acid to remove rust from cans. Based on some recent posts, I am going to try to summarize the tips in this post.
If you have any comments for pros/cons/additions/corrections, please post them below and I will edit this top post as we go.
Where do I get oxalic acid?
You can buy oxalic acid online (Amazon) or at local stores. It is typically sold in crystal form in 2lb or 5lb bags and is sometimes called "wood bleach". Just look for the name "Oxalic Acid" in 99% purity. As of January 2025, you can buy oxalic online for about $8/pound.
Does oxalic acid come in different strengths?
Oxalic acid itself DOES NOT come in different strengths. The types you can purchase online are noted as 99% pure.
Does oxalic acid have a shelf life?
The experience of the users polled is that, NO, oxalic acid DOES NOT have a known shelf life. It can sit for years - in powder form - with no affects.
What ratio of oxalic acid to water should I use?
There are many opinions on this but the general consensus is to use an oxalic acid to CAN ratio of about 1 tablespoon per can. This will typically be about 1/4 cup of oxalic per gallon of water, i.e. you can fit about 4 cans in a 1 gallon bucket.
There is a lot of discussion on various ratios depending on the amount of rust on the can, condition of the paint, etc. This is just a general starting point, you may find that you will add or reduce the amount of oxalic acid based on experience.
What temperature of water should I mix with the oxalic acid?
This is a little trickier.... Typically, you would use warm to hot water. However, hot water has a tendency to fade brighter paints like reds/bright blues or may take the paint off of some cans that have poor paint jobs, i.e. 70's pull tabs. Be careful and it's better to practice with just "warm" water.
How long should I soak cans in oxalic acid?
This will depend on the amount of rust on the can but a general rule of thumb is to do a first check after 15-20 minutes (check at least every 30 minutes thereafter). To really see how well they are doing, it is recommended to take the can out of the acid bath and clean them again under a warm water bath with dish soap and a toothbrush (just like your initial cleaning). This is another one that you will figure out as you gain experience.
Be careful not to "oversoak"!
Cleaning and Soaking TIPS!!
- Clean your cans thoroughly before using oxalic acid by using a good mix of warm water, dish soap, and tooth brush. This would include removing any mud or debris from the inside of the can. Any dirt, mud, etc will dilute the acid mix.
- Always add the acid to the water, per your high school chemistry teacher.
- Wear rubber gloves when handling the acid and/or the soaked cans.
- Soak cans outside or in a well ventilated area.
- Use just enough water to cover the cans you are treating....don't put 1 can in a 5 gallons of acid/water.
- Totally submerge the can by filling it with the oxalic acid mix as you sink it in the acid bath. It is obviously not necessary to clean the inside of the can but it's a lot easier than trying to hold the can down with some kind of weight.
- Practice soaking cans to gain experience by using cans that don't have value to you.....don't soak an Apache cone top as your first can!!
- Don't soak cans in direct sunlight as they will have a tendency to "green up".
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