I've read a number of questions about how a dragon would or could breathe fire, and what substances would allow them to do so, and alcohol or ethanol has always been mentioned and shot down as alcohol would diffuse into the blood and kill the dragon. So:

  1. Is it possible for an organism such as a dragon to evolve a community of microorganisms in its gut to produce alcohol given the correct diet?

  2. Is it possible for that organism to collect the alcohol and store it in a non-cellular gland or structure to be sprayed out of its mouth and ignited in some way?

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    $\begingroup$ Wait, it would? Do I have pee in my blood? o_O $\endgroup$ – Devsman May 18 '16 at 19:53
  • $\begingroup$ Urea? Yes. How the else could your kidney work? $\endgroup$ – The Nate May 18 '16 at 20:06
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    $\begingroup$ @TheNate Sure, but not because it leaked from your bladder. The point is that given the need a liquid can be separated in a biological system. Stomach acid is a better example, and shows just how challenging a problem a biological system can solve. $\endgroup$ – wedstrom May 18 '16 at 22:25
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    $\begingroup$ Several answers state that alcohol is plausible, but isn't the real question wether living organisms can produce alcohol in high enough concentration to be flammable? For alcohol to ignite it must be above the flash point. If we assume that dragons have a body temperature in the same range as humans, that means its ethanol fire-fuel must reach at least 20% concentration. engineeringtoolbox.com/ethanol-water-d_989.html Fermentation only yields 15% alcohol. So, your drunken dragons would need a higher body temperature (meaning higher metabolism etc) $\endgroup$ – Guran May 19 '16 at 6:39
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    $\begingroup$ why alcohol? Surely a gas would be simpler for causing flame breath - a bit like lighting your farts - or belches in this case. $\endgroup$ – gbjbaanb May 19 '16 at 9:18

This isn't that outlandish. There are already examples of folks who consumed some form of brewer's yeast that can get drunk when eating carbs. The yeast colonizes their GI tract and converts the sugars to alcohol, which is then absorbed into the blood stream.

A proposed system would probably require a dedicated "fermenting sac" lined with cells that actively pull away alcohol and dump it into another sac lined with acellular material or cells that are either very resistant to alcohol or secrete a film that is (think of how the gallbladder collects and concentrates bile produced by the liver). This would keep the alcohol level in the fermenting sac low enough to not kill off the fermenting organisms and concentrate enough alcohol in the storage sac to be flammable. Of course it is very difficult to biologically drive a gradient like this (pulling from a low concentration to a high one) so this will be a high energy consuming process. The dragon would need a robust alcohol degradation pathway in the liver to deal with any alcohol that got into the blood stream as there would inevitably be at least some leakage.

The alcohol could be stored in a non-flexible space (i.e. lined with corrosion resistant enamel, dense keratin [horn], chitin, or something) but it would need to be transferred into a muscle lined space in order to be propelled out (like how your stomach can contract to vomit), the space would need to be collapsible (like an accordion), it will have to be "flung" out via mechanical motion, or dispersed into the airway and moved out via exhaled air. But this would probably cause the dragon to inhale alcohol rich fumes unless it has a dedicated "blowhole" like an aquatic mammal for just this purpose.

Igniting the alcohol would be difficult via a pure biological process but perhaps the dragon could have an organ that is purposefully loaded with flint and steel (somewhat analogous to birds eating rocks to aid in mechanical digestion, i.e. the dragon ejects the alcohol from it's mouth and strikes teeth together that have embedded minerals that create a spark). Or it could have something that ignites upon exposure to air like a more volatile alcohol/gas mixture or elements like Lithium (which are horribly toxic in their own right but could be maintained in much lower quantities).

But the volume of alcohol to provide a useful stream of fire would be pretty large, severely limiting the number of times a dragon can breathe and refill the reservoir. A more payload efficient effect would be to create a aerosol cloud that is then ignited like a thermobaric fuel/air explosive but this isn't what is usually depicted in media.

  • $\begingroup$ I recall a species of aquatic snail living on volcanic vents on the ocean floor that have metallic shells. Could dragons evolve something similar? Like a forked tongue that has a bulb of minerals or metals on the tips that it can knock together to produce a spark? $\endgroup$ – The Mighty Squish May 19 '16 at 19:57
  • $\begingroup$ Can't see why not. This doesn't seem like something that can naturally evolve so if it is designed in some fashion anything is possible. But then again, there are creatures with truly bizarre hunting/defense mechanisms in our world so who knows? Perhaps ejecting a high alcohol stream alone was the natural evolution, but once the dragon got smart it figured out it could be flammable and developed tools for that purpose. $\endgroup$ – Jason K May 19 '16 at 21:12

Considering the number of creatures that can store enough venom to kill large animals, one would have to assume that living things can generally evolve the means to store toxins safely.

The bombardier beetle (Carabidae) stores hypergolic and somewhat toxic hydrogen peroxide and hydroquinone in ducted glands. The skin of the poison dart frog (Dendrobatidae) contains a toxic chemical that causes disorientation and asphyxiation in every animal except the poison dart frog. The blue-ringed octopus (Hapalochlaena) has fatal neurotoxins in its saliva but it doesn't die from them or even drool very much.

The stonefish, box jellyfish, death stalker scorpion, Sydney funnel-web spider, marbled cone snail, and any number of snakes like the inland taipan, coral, mamba, and blue krait, to name just a few famous killers, all happily make and store concoctions that would make Lucretia Borgia shudder.

There's no reason why a creature could not evolve a gland to store ethyl or even methyl alcohol without poisoning itself.

  • $\begingroup$ Great answer---esp. Borgia. There is also the welcomed colony critters: the beetles that secrete a food for microbes or (in another species) lichens, or the komodo dragon, or, for that matter, all ruminents. Cows hold grass that they they can't digest in their rumen and then spit it back into their mouth once they've given the protists their shot at it. Bonus points since that involves the creation of EtOH. $\endgroup$ – The Nate May 18 '16 at 20:14
  • $\begingroup$ They wouldn't necessarily have to store it in a gland, really. Animals like the Slow Loris and the Tree Shrew feed on fermented fruits all day long and take in a fair amount of naturally brewed ethanol/alcohol. Suppose your dragon either consumes something that has the alcohol (or as a byproduct brews in it's stomach), it could have built a natural tolerance to just have it in it's stomach to regurgitate later. $\endgroup$ – Aaron Lavers May 19 '16 at 1:30
  • $\begingroup$ Storing alcohol is certainly possible. How about the "ignite it without buring itself" part? Heat resistant nostrils seem tricky, although some kind of a surface layer that needs to be replenished after each fiery breath might be plausible (even if expensive). $\endgroup$ – John Dvorak May 19 '16 at 7:31
  • $\begingroup$ @JanDvorak Theoretically you could use the same method as a flamethrower and have the igniting substance external to the general body structure, almost like the light/lure or an Angler Fish. $\endgroup$ – Ieuan Stanley May 19 '16 at 13:18
  • $\begingroup$ @Aaron Lavers: Earthly creatures with a high tolerance for alcohol manage it by rapidly converting it to sugar before it poisons them. Also, I assumed a specialized gland rather than the stomach because the alcohol would interfere with normal digestion. -- OTOH if dragons are sufficiently different from the creatures we know, alcohol could form a major part of their diet. In which case fire-breathing might be nothing more than mild to moderate indigestion. $\endgroup$ – A. I. Breveleri May 19 '16 at 19:19


Many animals use projectiles and even more use poison, some creatures like the Spitting Cobra even use projectile poison. Thus there is no evolutionary reason why a creature couldn't spit poison, now at a high enough concentration alcohol is poisonous so by that logical a creature could indeed evolve to spit alcohol as a poison (most likely directed at the eyes). Now all that is needed is a catalyst and the alcohol with light aflame. Here is yet another example we already have, electricity is a common weapon many animals use All that is needed is for a land creature to use electricity (maybe for mating or threatening) somewhere near the mouth and whoosh, you have alcohol based fire breath.


I recall that in the Elric series by Michael Moorcock, the dragons of Melnibone had saliva that was a highly-flammable oil. They kept rocks in their gizzards to aid in digestion, and with a bit of training, could use them to light the saliva. Obviously, this is more helpful in terms of flybys against wooden warships, which worked well with Melnibone being a naval power.


If the concern is about alcohol diffusing into the blood through its detrimental effect on cell membranes and miscibility with water, I could see an oily sort of mucus secretion being used on the inner lining of the "sac" and throat/mouth. While ethanol will partially dissolve oil, the solubility depends on how much water is available as well; if the dragon's body carefully produces the ethanol in a relatively pure form sealed from other moisture, the continuous secretion of mucus would keep the living cells safe.

I imagine the dragon would have another (possibly larger) chamber in addition to the "fuel sac" where sugars are stored to ferment; this chamber would maintain conditions ideal to the yeasts or bacteria that lived there, to maximize ethanol production. This chamber would probably also have some mechanism developed that would help siphon off excess water during the process so the ethanol doesn't dissolve the mucus.

As an added bonus, if its composition is right, the oils in the mucus would make the fuel all that much nastier when the dragon breathes fire -- think about tiny aerosolized droplets of oil being ignited, and then sprayed on things.

The drawbacks

  • The dragon would have to periodically "burp" off excess fuel as the continuous mucus secretions were dissolved into the alcohol, unless a certain equilibrium were reached (which might not be comfortable for the dragon)
  • If the dragon gets ill or dehydrated, their fuel sac might not be able to produce enough mucus to protect the lining. Have you ever had your nose dry out when you were sick? Now imagine snorting Everclear with that dried out nose.
  • The dragon would have to eat continuously, and unless their body had a process for efficiently converting fats and proteins to sugar, they'd have to eat lots of sugary stuff to process and ferment into ethanol.
  • $\begingroup$ Have you ever had your nose dry out when you were sick .. if only, quite the opposite usually. $\endgroup$ – gbjbaanb May 19 '16 at 9:15
  • $\begingroup$ When a dragon became ill he might have to 'dump' his flammable fluids to protect himself. Sick dragons would not necessarily autointoxinate, they would merely be unable to breathe fire. $\endgroup$ – A. I. Breveleri May 19 '16 at 14:42
  • $\begingroup$ @A.I.Breveleri that would be a good protection mechanism -- better to not be able to breathe fire for a bit than to die of your own internal fluids! $\endgroup$ – Doktor J May 30 '16 at 23:24

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