According to Jean Lenoir of Le Nez du Vin, "soapiness" is a flaw that can occur in wine and fortified wine. "Some fatty acids produced by yeast during vinifcation ca turn up in the wine as salts: these are called "soaps." Caprylic acid salt (decanoic acid), is a good indicator of the soapy taste that can sometimes be perceived in wines, especially white wines, as soon as they are casked." I had a bottle of Martel Cognac VSOP a long time ago that tasted soapy to me. To this day I can't drink Martel.
There is a problem with most wine consumers and many wine professionals. They don't know about all the different flaws that can occur in a bottle of wine, and they certainly don't know how to recognize the various flaws. To remedy this, I'm developing a wine party kit that includes a game to help learn how to detect a flawed bottle of wine. Contact me directly if you'd like to learn more.