Testing ESBIT Boiling

One of the main requirements of winter ultramarathons is carrying a stove so that you can boil water/snow and cook food. Most participants carry one of three different types of stoves, with one of them being an ESBIT solid fuel stove. I’m not going to review stove types in this blog, but am going to talk about different techniques to help use your ESBIT stove more efficiently.

ESBIT is a solid fuel stove that uses tablets of fuel to heat water. You simply place a tablet into your stove and light it on fire and wait. It’s incredibly simple to use, and works at any temperature that you can make a flame. They are lightweight, and easy to pack into a kit, which makes them very popular for endurance events. However, they’re not without their challenges.

Many people experience issues trying to get water all the way to a roiling boil with an ESBIT stove, because similar to a campfire, they are not controlled and contained like a liquid fuel type stove. However, with a few adjustments you can get great results. In order to demonstrate a few different aspects of using an ESBIT stove, I did some testing of different configurations, and timed how long it took to get the water to boil.

One note: A full boil is around 212°F (100°C) at sea level, and a boil should always be your goal when doing any cooking, especially with unfiltered water. However, according to the WHO, you can make food safe at lower temperatures, even down to 150°F which is quite easy to obtain with any stove. Having said this, I’m not a scientist, so please endeavor to do some research on your own, and make your own determinations.

For this test I performed 5 different scenarios.

  1. Uncovered pot, no heat/wind shield, 1 ESBIT tablet
  2. Covered pot, no heat/wind shield, 1 ESBIT tablet
  3. Covered pot, no heat/wind shield, ESBIT tablet broken in two pieces
  4. Covered pot, heat/wind shield, 1 ESBIT tablet
  5. Covered pot, no heat/wind shield, 2 ESBIT tablets

For each test I set up just inside my garage with an air temperature around 52°F (11°C) and very, very light wind. I used a stainless steel GSI Glacier pot, and 2 cups (16oz/472ml) of room temperature water.

Uncovered pot, no heat/wind shield, 1 ESBIT tablet

For this first test I wanted to set a baseline of the simplest setup. This meant that there was nothing stopping the wind from causing issues, and the heat could escape from the top of the pot unrestricted.

I started seeing small bubbles around the 3-4 minute mark, and larger ones by minute 8. The ESBIT tablet burned out at just under 12 minutes, and the water reached a final temperature of 190°F (88°C). This is just above the temperature required for “simmering” and there were lots of little bubbles rising to the surface for the final 3 minutes.

Despite not reaching a full 212°F (100°C) boil, I would still be comfortable using this water to make my meal, depending on the source. If I was taking it from a stream I’d probably grab a second tablet (or half a tablet) and keep the heating going a bit longer, but if I was using a well, or clean snow, I’d feel OK.

I’m not surprised that this test did the worst, as the heat from the flame was being lost all over the place. For all the remaining tests, I added in a lid.

Covered pot, no heat/wind shield, 1 ESBIT tablet

The second test was the same as the first, but with an aluminum foil top to the pot. Many pots come with covers, but since I was using a steel cup, I had to fashion one on my own. The design of the lid isn’t the most important thing, simply stopping heat from escaping is the key.

I noticed the smaller bubbles much sooner in this test, closer to the 2-3 minute mark, and the larger bubbles near minute 7. Although the water never reached a rolling boil before the 12 minutes were up, it did get to 202°F (94°C) which is pretty darn close. I’d feel totally comfortable using this water for my meal as it spent many minutes in a simmer with large bubbles escaping consistently.

It makes a lot of sense that a cover on the pot would help, as heat travels up and if you trap it within the pot you’ll stop that warm air from escaping and cooling your water prematurely.

Covered pot, no heat/wind shield, ESBIT tablet broken in two pieces

I had read somewhere that if you break an ESBIT tablet into two, and place it on it’s ends, it provides more heat and can make your water boil quicker, so I decided to give it a try. Right off the bat I could see that it was providing a larger flame. I was getting small bubbles closer to 2 minutes, and by 6 minutes the large bubbles were going strong.

That’s when everything stopped though. With the tablet broken in half, the ESBIT died just under 7 minutes into the test. That meant that my water never got above 185°F (85°C). That’s the lowest temperature of all of my tests, and given how short the duration was, I’d probably not feel too great about using this water for cooking or drinking.

One option could be to use tongs and swap in more half-tablets, but that seems like a lot of work.

Covered pot, heat/wind shield, 1 ESBIT tablet

Finally, I got to the test I was most looking forward to. The issue with any stove in winter is that the air surrounding the cooking vessel and the stove itself is cold. Heat dissipates quickly, and by having so much surface area exposed to the open air, you lose tons of efficiency.

For this test I fashioned a simple wind and heat shield out of aluminum foil, and made sure it was high enough to not just cover the stove and protect it from wind, but also provide a heat barrier around the pot itself. The rationale is that by trapping heat around the pot, you diminish the energy loss of the system overall. This means your tablet provides way more heat in a lot less time.

The test proved this perfectly. The small bubbles appeared on schedule between 2.5-3 minutes, and the large bubbles were going strong by 7. However, by 9:10 I had a FULL rolling boil going with a temperature of around 210°F (99°C). Because I’m not at sea level, this is about the temp I needed for a full boil (also accounting for thermometer inaccuracies).

Because of how efficient this system was, I could actually boil water for a full two minutes longer, until the ESBIT tablet died. That means that any worry about contaminants was long gone, and there are no issues using this water for any purpose. This test ended up being the gold standard of all of my tests, turning in the best result by far.

However, I still had one more test that didn’t end up going quite to plan.

Covered pot, no heat/wind shield, 2 ESBIT tablets

For the final test I wanted to see what two ESBIT tablets would do, without a wind/heat shield. I loaded up my stove with two tablets and started the test. Soon I noticed that the flames were getting really intense. There were large licks of red and yellow making their way up the side of the pot.

I reached the small bubble phase between 2-3 minutes, but then I noticed a problem. The bottom of my ESBIT stove has holes in it for ventilation, and the ESBIT tablets were starting to melt through these holes and onto my workbench. I started seeing flames coming from under the stove and decided that this test was over.

I quickly extinguished the entire fire with some room temperature water (ESBIT’s die really fast in water) and carefully set the stove on the driveway to cool. My workbench had a couple scald marks, but, thankfully, seemed no worse for wear. I got everything cleaned up and decided I wouldn’t repeat this test. At least not with the current ESBIT stove that I own (pocket stove).

Even if you could fix the fire hazard, I don’t see a lot of advantage of this method. The flames were shooting everywhere, which is just wasted energy that isn’t helping heat your pot. The biggest issue isn’t the amount of heat, but the level of heat dissipation. Controlling that aspect is the key to success with a stove like this.

Conclusion

As you can see, the best method is to use a wind/heat shield, and a pot lid, to keep all of that energy contained where you want it to be. ESBIT tablets burn hot enough to get the job done, but you need to be cognizant of your environment.

Additionally, there are a lot of different options for stoves and pots that can do a better or worse job. ESBIT has a whole host of different options on their site that use different material and designs. Additionally, many camp meals don’t require a full 16oz (472ml) of water to cook. Often you can get by with a lot less water for simply eating food which is a lot quicker to heat.

I hope you found this testing informative, and maybe inspiring to try a stove method that you may not have worked with before. ESBIT’s are a great option in frigid cold, and can help keep you alive in the dead of winter. Plus, simple aluminum covers and wind/heat shields can be fashioned cheaply, and are very lightweight to carry. Add to this the really economical cost, and ESBIT stoves have a real advantage over some of the other stoves out there. Especially when dealing with the frigid cold of a January night in Minnesota.

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