Mushrooms consist of mycelium and fruiting bodies - which are made of a cap and a stem. Fruiting bodies and mycelium may contain different compounds from each other, so it is advised to know what is used in the supplement you are looking for. Using both of mycelium and fruiting body in a supplement is called full spectrum supplement.
After knowing which part of the mushroom was used, either mycelium or the fruiting body we can proceed with understanding what method has been used to process the mushroom and its extraction method (if it has been extracted).
There are trace amounts of mushroom mycelium inside the myceliated grain (colonized grain spawn). The mushroom itself cannot be separated from the ground grains and thus it is not possible to get a pure mycelium product which in the end contains all of the grain and a bit of mycelium mixed together.
Another way would be to get only the fruit of the mushroom, dehydrate it and grind it down to fine powder. This approach contains only the ground mushroom body with no additional grain. Due to the nature of mushrooms and their building blocks it might be tough for our body to extract all the compounds from the fruit due to chitin - a tough compound used to build cell walls inside the mushroom, which we humans do not digest.
If you want to get to the next level extraction is the way to go. Extraction makes the mushroom compounds bioavailable which means that we can absorb them. Usually it is either done with alcohol or water.
Process of extraction can be done with water extraction, alcohol extraction or both (dual extraction). Colonized grain spawns are not extracted so extractions only apply to ground dried fruiting bodies of mushrooms.
Extraction method depends on the type of compound we are trying to extract from the fruiting body. For example, beta-glucans are compounds responsible for immune supporting benefits of mushrooms and they are hot water-soluble - it means that no alcohol is used to extract these compounds.
There is also a case where both of the methods are used - it is called dual extraction. More often than not they are not used simultaneously but rather one after another. It can be alcohol extraction first and then hot water extraction or the other way around.
Label on the packaging can tell you everything you need to know about the supplement you are trying to buy. You can check the level of active compounds (beta-glucans, triterpenes and cordycepins etc.).
Look out for "Other ingredients" section. If it is a ground myceliated grain it will be written there with other things that were used during the manufacturing process. Such case could be "flow aid" due to the nature of mushrooms extracts being sticky it would be used to help the flow of the mushroom extract through the manufacturing system.
Another thing to look at would be if the supplement facts panel is exaggerating the amount of mushroom present in a product. Let me explain, when the mushrooms are extracted most of the fruiting bodies would not end up in the final product.
For example, due to the nature of concentrated extracts it can take around 4 kilograms of Lion's mane (Hericium Erinaceus) fruiting body to get 1 kilogram of extract. It means it is 4:1 extract ratio.
Some manufactures will use this to fool you by saying there is 4 times more mushrooms in the product than there actually is using equivalent weights. This can be spotted if a 500 mg capsule contains 2000 mg of mushroom inside it.