There is a persistent myth that matcha will oxidize if it comes into contact with metal. I often see this repeated in videos on TikTok and Instagram, usually by health influencers but tea companies have also been guilty. I thought it was time I addressed it in a blog post. Here is everything you need to know about the myth of matcha and metal.
The Myth of Matcha and Metal
There is a belief that contact with metal can oxidize matcha – ruining the taste and decreasing health benefits. The basis of this theory is that catechins in tea act as a bonding agent with ions in stainless steel, causing the metal to leach into the tea. Catechins are antioxidants, one of the main health benefits associated with tea. The evidence people often point to is that matcha changes color when it is left in a stainless steel cup.
Why It Isn’t True
This all sounds a bit like fear-mongering to me. Here are some reasons that show why this myth doesn’t hold water.
- People have been drinking teas of all kinds out of metal thermoses for a very long time. Surely we’d all have been poisoned with metal by now.
- All teas oxidize when exposed to oxygen. This happens regardless of what material the container is made out of.
- Matcha comes into direct contact with metal at many stages of production.
- Matcha and other teas are often packaged in bags and tins that are made out of metal.
- Matcha is designed to be enjoyed immediately after whisking. It should not be left to sit long enough for oxidation to happen.
Metal forks and whisks aren’t the best tools for making matcha, but not because they might cause oxidation. They just don’t produce the same results as a bamboo chasen. There are still lots of other ways you can make matcha though!
What the Experts Say
I reached out to some of my favorite matcha vendors to get their take on the myth of matcha and metal. Here is what they had to say.
SC from Naoki Matcha said that in their experience they often use stainless steel utensils or canisters and they do not affect the taste of tea. If you care about taste there are more important things to worry about. For example: temperature, humidity, and light all result in oxidation that ruins many natural foods over time (not just matcha but also tea, nuts etc). The best way to preserve peak flavor as long as possible is to refrigerate matcha after you open it. That’s much more important than the material of your utensil or container.
Ian from Yunomi hadn’t heard of this before, he pointed out some of the holes in this theory. The claim is that the stainless steel is leaching metal into the liquid. However, you’re not cooking when using matcha in a thermos. Leaching also occurs more with acidic foods, and matcha is actually slightly alkaline. Higher-quality matcha also contains fewer catechins, making chelation even less probable. Black tea is more acidic but green tea is more alkaline.
Lauren from Mizuba Tea Co. went right to the source and asked her partners in Japan. They said that logically matcha can be oxidized by touching stainless steel, but there needs to be another component to make it happen such as water. Once Matcha is mixed with water (especially hot water), oxidation can occur rapidly. It is ideal to consume the matcha as soon as you make it. Keeping it in a bottle, regardless if it’s stainless steel or not, also oxidates matcha and changes its taste and color.
What’s another tea myth that I should tackle? I’d love to hear from you in the comments below!
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We were treated to a free coffee at work today and I chose a strawberry matcha latte. When I got home after obtaining the coffee, I poured it into one of my cups that is lined with stainless steel and added some ice cubes. I had gotten the same tea the day before, drank it out of the plastic cup it came in and it was wonderful! This latte tasted disgusting in that metal lined cup. I immediately poured it into a ceramic cup, let it sit for a few minutes and it tasted wonderful. I had no idea and had never read anything about drinking matcha. I will never drink it out of a metal cup again!
The thing about matcha is that it is meant to be consumed immediately. The tea was clump up and settle if you let it sit too long, which will definitely make it not taste as good.
I am confused. Isn’t the end of the article (the part where the japanese adviser said that matcha does get oxidised by stainless steel) in direct contradiction with the whole point that was made at the beginning (that it was all a myth and matcha met metal at some point in the supply chain anyway ) ?
Also, it is said to drink it quickly when made using metal tools, but to me, it is still vague. How quickly (so we at least have an idea of the longest time that is ok) ?
I actually just returned from Japan where I visited tea farms and matcha factories so I’ll be sharing more about that on the blog soon. Metal isn’t really the issue here. Mixing water with matcha powder adds oxygen. Combined with a warm temperature, this expedites oxidation of the polyphenols that naturally occur in all tea. It changes the color as well as the taste. Using cold water should help slow things down but all tea will oxidize eventually if left to sit. Matcha is prepared as a suspension rather than an infusion so it should always be consumed quickly. The tea leaf particles will settle and clump up on the bottom of the container within a short time period. If you want something that you can leave in a thermos for a longer period of time, you might want to look into leaf teas that have a similar taste such as sencha or gyokuro.