Cooking Dehydrated Meals in High Altitude
What is up with high altitude food?
Dehydrated food- every outdoor enthusiast’s favorite. Whether you’re biking along the coast, skiing a day in the backcountry, or even just feel like going out for one of those 2,650 mile long walks for 5 months, dry food and its crunchy to chewy transformation is a popular choice among the adventure community.
However, despite the ease and practical benefits of storing and preparing backpacker meals, there is one hiker bugaboo that can heed hiccups to their cuisine rehydration routine: Altitude. Slow cook times and underperforming methods of heating often trouble high elevation climbers who aim to put warm food into their empty stomachs.
The challenge regarding high altitude food is associated more with science and subsequent equipment technicalities than with the food in and of itself. When we look at what causes these challenges, it is clear that the high hiker wages war on a single basic complexity of atmosphere- PRESSURE.
How do hikers combat the effects of pressure? Well to learn, it is best to first understand how pressure plays a role in halting hydration.
“Ummm you mean boiling?”
Yes, vapor pressure is a measure of the tendency of a material to change into the gaseous or vapor state as the material increases with temperature. Basically, when the molecules inside water heat up and loosen, bouncing around to the point where they exceed the rate at which the molecules in the surrounding air are bouncing around, then the water will release into the air and begin to boil. Much of these dynamics depend on gravity.
Camp on Mt. Hood at approximately 10,000ft where water boils at 89.8 C (193.6 F)
Gravity is the force that both cracks iPhone screens and compresses oxygen at lower altitudes. So, as the hungry hiker goes up in altitude, and less oxygen around them is compressed on top of itself, the pressure decreases in the air and therefore less heat is needed to bounce water molecules around to the point where they escape out of their Jetboil. This low pressure environment encourages water to boil at a lower temperature and because water cannot exceed the temperature at which it boils, the hiker must wait longer for the cooler water to warm their dehydrated food.
Dehydrated foods will rehydrate at different rates of time depending on their volume (how large the pieces of food are), their fat content and the amount of moisture required in each item to bring it to a recognizable consistency when eaten. Heat simply accelerates this process by opening the pores in the food and allowing water to saturate it quickly. Assuming the food is already cooked, there is no required temperature to safely prepare dehydrated food and therefore at high altitude one simply needs to wait longer for foods to become ideal to the taste.
If waiting is not your thing, properly pre-cooked dehydrated food at low pressure can always be eaten al dente- meaning that slightly less hydrated food still contains the calories essential for the activity at hand but may just be a little crunchy and unfamiliar to the taste. Food For the Sole also offers a variety of cold soak meals that require only nominal temperature water therefore avoiding the need for the heating of liquid all together.
Isobutane vapor pressure.
Once again, that pesky pressure stuff returns to make make using stoves a real pain in the pot.
Less to do directly with elevation per se, an added condition of being high in altitude is a dramatic decrease in temperature. As any backcountry skier or snowboarder will explain (in between expletives), a cold stove can suffocate the stoke during a day of shred. This again has to do with the boiling point of butane and propane.
In a normal fuel canister that you may buy for your Jetboil there is a mixture of isobutane, of which boils at -12 C (10.4 F) and propane, of which boils at -42 C (-43.6 F). At room temperature, both fuels boil into a vapor that sits at the top of the canister and is discharged when attached to a stove. However, the cooler the outside temperature gets, the lower the vapor pressure becomes in the canister, therefore creating less fuel in a gaseous state to be purged into the stove system. The main culprit being the butane, which at 10 degrees Fahrenheit can easily cool close to or below its boiling point in normal atmospheric conditions.
No boiling= no vapor for your stove to burn.
In addition, propane has a lower boiling point than butane, so it will vaporize disproportionately faster in cold weather until only butane remains in the canister. Because butane vaporizes much less effectively at low temps it causes cold canisters to initially produce flames that diminish over the course of several minutes.
On top of that, the natural tendency of the fuel as it’s being released is to cool as a result of energy being displaced in its transformation from liquid to vapor. This is not only the cause of ice formation on canisters, but yet another scientific offense to proper stove operation in cold temperature.
“Great, science and stuff. What do I do about it?”
Backcountry skiers and snowboarders are often troubled with the technical difficulties associated with cooking at cold temperatures and high altitudes.
Well the answer is: not a lot. Technology continues to improve regarding camp fuel and stoves, but the fundamental challenges of temperature and pressure won’t simply go away. One technological solution is an inverted canister stove. This works by removing the dependence on vapor in the canister itself by preheating the fuel in the input line before it reaches output at the jet valve. While the canister is inverted, pure liquid fuel runs through the gas line and over a “pre heat loop” that raises the temperature of the fuel mixture to vaporize just before it becomes flame. Stoves like the Jetboil Joule or the Kovea Hydra are becoming increasingly effective at heating in cold temps, but their drawback is a greater weight and cost which potentially edges them out among their highly efficient summer stove competitors.
Kovea Hydra with preheat loop design shown.
Another straightforward and easy solution is to use a stove with a wider regulator valve to produce more fuel at lower pressure. This does remove a common fail-safe in modern stove systems, but by being conscious and careful, an operator can help get a little more flame performance out of a cold fuel mixture.
Alternative fuels like gasoline or kerosene can be used in effect as well, however they are much heavier to carry and often involve charging systems that can be prone to failure in low temperatures.
The best and most effective solution for most hikers looking to combat a cold stove is to both make sure that they are using isobutane and to pre warm canisters before use. Isobutane has a lower boiling point than regular n-butane. So, when choosing a fuel mixture for a cold camping trip, be sure to spend the extra dough and invest in an isobutane/propane mixture instead of its molecularly similar brother n-butane (BP= -1 C [30.2 F]).
Also, when the prospect of cooking in the near future arises, take that poor, cold and lonely canister out of your backpack (its dark in there!) and snuggle it up close to your body inside your jacket where it’s warm and cozy for at least 30 minutes. Not only will you make a hard working and under appreciated isobutane canister feel warm and loved, but in return it will help the fuel mixture vaporize in the canister to provide higher flame performance when you go to heat up that long anticipated dehydrated food.
In conclusion, the challenge of using a stove at high altitude is just one that ranks among the many trials that an outdoor adventurer will naturally encounter while in the mountains. If one wanted everything to be easy, than one is perhaps better suited for watching mountaineering documentaries on the couch. The faulty operation of a stove and the crunchy consumption of dehydrated food high in the air will no doubt be overshadowed by the triumph of the climb or the euphoria of the surrounding scenery. This being said, there are a few tricks that help to make eating dehydrated food a little easier and more rewarding in a situation where your body calls for calories:
- Wait longer at high altitude for cooler boiling water to warm up and rehydrate food. Or consume food with crunchy consistency.
- Avoid dehydrated meats and fats in dehydrated meals that take the longest and most amount of heat to rehydrate.
- Invest in isobutane mixtures versus n-butane mixtures.
- In cold weather, pre-warm fuel canisters in a jacket for at least 30 minutes before operation. If possible, have two canisters available to switch in and out between warming and operation.
- Invest in cold weather specific stoves that use inverted canisters and wide jet valves.
Links to further reading can be found below:
- Information on fuel mixture science.
- Adventures in stoving in cold weather.
- Wiki article on boiling point and vapor pressure.