Testing Medicinal Mushrooms for Starch Using Iodine
Iodine testing is a simple way to check for starch in medicinal mushrooms like Reishi, Lion’s Mane, and Turkey Tail. Starch can indicate low-quality products or fillers like grain-based mycelium, which dilute the beneficial compounds such as beta-glucans. Unfortunately, a significant percentage (up to 70% according to some research) of store-bought mushroom extracts contain large quantities of startch, and low quantities of bioactive compounds. You can learn more about why there are so many low-quality products here if you are interested.
Why Test for Starch?
High-quality medicinal mushrooms should have minimal starch. Excess starch may mean the product includes fillers or is made from myceliated grains, which are known to contain significantly less bioactive compounds compared to high-quality mushroom fruiting bodies.

In the image above is a typical “myceliated” grain which is often used in low-quality supplements. Learn more about this here.
How It Works
Iodine reacts with starch to create a blue-black color. This reaction occurs because iodine binds to the starch structure, making it easy to see even small amounts.
What You Need
- Mushroom Powder or Extract
- Iodine solution
- Water
- A glass container
- Pipette or dropper
Steps
- Prepare the Sample: Mix a small amount of mushroom powder with water.
- Add Iodine: Use a dropper to add 5-10 drops of iodine to the solution.
- Check for Color: If the mixture turns blue-black, starch is present. No color change suggests minimal starch.

A good-quality extract should look like the cup on the left. It may be lighter or slighly darker depending on the mushroom and quantity of powder you added. Dark coloration, like that on the right, indicates a significant quantity of startch!
If you conducted this test feel free to let us know your results! If your product came out positive for startch, check out our Supplement Buying Guide to know what you should look for in a quality product!
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