Can you put martell congac in a glass under a congac/brandy warmer?

Sure, but make sure you adjust the flame properly. You merely want heat|||Here's a trick I learned in an upscale bar as a bartender... Use a small cordial, snifter style or rocks glass to put the congac in. Then, we always kept a pot of hot water on the coffee warmer (for tea, whatever...). I got a large glass with a wide mouth and put some hot water in the glass, about 1/3 of the way up. Lastly, I inserted the smaller glass into the larger one and the radiant heat from the water heated the cognac or brandy. Just let it sit for a minute or so, take it out and wipe the warm water off of the glass.