Common preservation agents include sulfur dioxide gas, brine (salt solution), and dilute sulfurous acid — all intended solely to maintain the mushrooms in a stable state during transit. The choice of agent does not change the classification within this heading, provided the product remains unsuitable for immediate consumption. If the treatment renders the mushrooms ready to eat without further processing, classification may shift to a prepared-mushroom provision under Chapter 20.

Heading 071151 covers mushrooms preserved by moisture-retaining methods (brine, SO₂) that keep the product in a near-fresh state but unsuitable for direct consumption. Heading 071231 covers mushrooms that have been dehydrated — air-dried, sun-dried, or otherwise dried — reducing moisture content substantially. The physical form and preservation method are the key distinguishing factors; a customs broker should request supplier documentation specifying the exact treatment applied.