Cork coasters stained by water? Start with a damp-cloth wipe
Check the care label of cork coasters; a light wipe with a damp cloth is appropriate for IKEA 365+ cork coasters. Let them dry before stacking.
IKEA 365+ cork coasters are intended to protect tabletops and reduce noise from glasses. Their official care instruction is to wipe with a damp cloth. Other cork products may have different finishes, so check their own labels rather than assuming soaking or machine washing is permitted.