&gt; For it to taste bad quickly enough such a coating would have to be water soluble.<p>I question that.. There are some pretty powerful bitterants available for this sort of thing. You don&#x27;t need much denatonium benzoate to make something unpleasant to taste, for example: &quot;Dilutions of as little as 10 ppm are unbearably bitter to most humans.&quot; <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Denatonium" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Denatonium</a>