Does a lid reduce fuel use and how to tell if water is pasturized

[Jerry Adams]

https://backpackinglight.com/forums/topic/backpacking-stove-efficiency-part-1-pot-diameter-burner-size-flame-level/page/2/

according to that thread a lid doesn’t save any fuel when boiling based on an experiment inside.   There was a question raised about whether it would make any difference if it was outside and windy

I tried to verify on a 5 day trip.  Each day I boiled a pint of water with the lid on, and another pint with the lid off and measured the fuel use.  I normalized to 450 g of water raised 150 F degrees.  If the water weigh a little more I scaled the result by that much.  If I raised it more than 150 F I scaled the result by that amount.  etc.  I also measured the time and normalized it – I wanted to do a 4 minute boil time.  If I did it a little slower then that will reduce fuel use so I wanted to measure that.

results:

Basically, the results varied for reasons other than whether the lid was on or not, but maybe I’m consistent with the gear skeptic who claims there is only a slight improvement when a lid is put on, and the weight of the lid exceeds any fuel weight saved

In run #1 (with lid) it uses 5.5 g of fuel, run #2 (without lid) it uses 6 g of fuel.  But run #1 took 4.5 minutes, run #2 took 4 minutes.  Since run #2 was done more quickly which results in more fuel used it’s unclear.

Run #3 and #4 were on the second day.  #4 was with a lid but it actually used up an extra gram of fuel – the opposite of what I’m trying to prove.  For #4 it got breezy which resulted in more fuel used which was greater than any benefit to having a lid on.

Runs #5 and #6 were on the third day.  Run #6 without lid was much worse, but again, I think it was because it was windy.

#7, #8, and #9 were on the fourth day.  For #7 it was calm, for #8 and #9 it got breezy – maybe 2 MPH.  There wasn’t any big difference between lid and no lid, but there was a 1 g increase from calm to breezy.

#10 and #11 were on the last day.  Very calm (but even then there were small breezes).  They took the same amount of time so the stove was turned up the same for both.  #10 with lid took 5.5 g of fuel.  #11 without lid took 6.5 g of fuel.  The time was about the same so the stove was turned up about the same.  I think this is the cleanest measure of lid vs no lid – about 1 g of fuel is saved by putting on the lid.  Which is about the same as Gear Skeptic measured.

All of this was with my heat exchanger windscreen.  The square aluminum part below is just a windscreen, which also reflects heat to the canister.  If the canister has any pressure to light, the reflectors will warm it up more as it burns.  The last day I had to use a lighter to warm up the canister. but once it got running the first time, it warmed up enough so I could keep lighting it. The last night the canister was mostly empty and it was 24 F with cheap butane but I could get it to work fine.

My take away is that a lid doesn’t matter but I like having a lid for other reasons, like keeping dirt out.  But how windy it is and how much I turn up the stove makes a big difference.

[Jon Fong / Flat Cat Gear]

If you like statistics, and have Excel, you can run a t-test to see if there is a difference between the means.

https://www.rwu.edu/sites/default/files/downloads/fcas/mns/running_a_t-test_in_excel.pdf

 

My 2 cents.

 

[Jerry Adams]

there are too many uncontrolled variables like how windy it was.  No amount of statistical processing would change that.  I think that wind and how fast you run your stove are the two variables that make more difference

[Jerry Adams]

On the gear skeptic video he says that you only have to heat up your water to 160 F to kill any bugs.  He shows that WAPI device with wax that melts to determine when you’ve reached 160 F.

That works good for solar heating to pasteurize water because it’s so slow and there’s nothing you can obviously see to determine you’ve reached that temperature.  The water will just be sitting there.

But from my video, when you’re heating from a stove, it’s pretty obvious when you’ve reached 160 F.  Better than watching that video is to experience yourself.

Up to about 160 F there are small bubbles on the bottom and a faint hissing from bubbles popping.  But, when you get to 160 F the noise noticeably increases.  At 170 F it’s even louder and big bubbles start forming on the bottom.  If you turn off the stove at that point, it is now safe to drink – any bugs have been killed.

If I am rehydrating something. I want to get hotter, pretty close to boiling, so it rehydrates better.  Black tea is supposed to brew at 195 F – at 160 or 170 F it won’t brew right.  I just wait until a puff of steam comes out from under the lid – which is maybe 200 F.

[Brian H]

I think it is a fact that a lid reducing the time to reach boiling.  That’s my my experience cooking both at home and in the backcountry, especially when the wind is kicking up.  Having a cold wind blow across an open pot of hot water can only cool it down, not keep it a neutral temperature.   I think it is reasonable that the sooner a body of water gets to a certain temperature (boiling), you would see a reduction in fuel use.  I’m interested to hear the holes poked in that argument.

[David Hartley]

This also runs counter to my experience. I wonder if the slight difference between lid and no lid would increase for larger amounts of water. Our pop-up camper has an underpowered propane stove and the only way we can boil a large volume of water for pasta is with a lid on the pot.

I always use a lid backpacking and boil small amounts of water, but backpacking stoves have plenty of power (if used with a wind shield), and it never occurred to me to test this given experience with larger pots and water amounts in other settings,

I guess I accept that the difference in fuel weight is probably less than the weight of a lid, at least for the small amounts of water typically boiled when backpacking, but I do like the lid to keep dirt out.

[DWR D]

All home cooks know that water boils faster with a lid on the pot. There is no question about this. There is no question about this.

Lids are also good for keeping critters out of your pot at night. I put a lid on my pot at night and a small rock on top of the lid… keeps the mice and bugs out. And in the pack, the lid keeps my stove, fuel canister, wind screen and bic lighter from spilling out into the pack. Can’t imagine ever not taking a lid to save the weight…

 

[LARRY W]

Thanks for testing out in the real world. May you be rewarded with hiker boxes holding almost full canisters. Still, saving a gram of fuel (test #10) is saving a gram of fuel. Say 15% for an efficient stove. Seems like the answer is a lid that weighs not much more than grams saved. Because all factors being somewhat equal I prefer couscous without grit.

And to reiterate a point already mentioned, how long the canister needs to last, factors in.

Thanks Jon also for beginning this conversation. Eye opener for sure and best of all debatable :-)

[Jerry Adams]

The gear skeptic did a good study that showed a lid makes little difference.  At really low speeds it helps a little more.  The total amount of fuel saved over a multi day trip is less than the weight of the lid.

This is very surprising to me, I always assumed a lid mad more difference

But his testing was inside with zero wind.  The question posed was if it’s windy would it make any difference?

And my answer from testing is the wind makes a huge difference, whether there’s a lid on or not.

And how fast you turn up the stove.  The gear skeptic characterized that pretty good in his controlled conditions.  When I run my stove on a camping trip each time I set the stove to a little bit different speed which confuses any results.

My testing was with a very good windscreen (I think).  The obvious question that I wonder about is how much do different windscreens or no windscreen make?

Maybe the next camping trip.

[W I S N E R !]

Is the UL community prepared to hear that it could take over two weeks on the trail before their lid is worth the weight it saves in fuel?!

I’m glad you did this because I was once beating myself up over whether or not to include a lid in a <24 hour fastpacking cook setup. I opted not to out of the rationalization that an Esbit tab is an Esbit tab, and if it boils the water regardless…then a lid is nothing but dead weight.

Jerry Adams, Destroyer of the Orthodoxy!

 

 

 

 

[Jon Fong / Flat Cat Gear]

Here’s my take.  If you are going SUL, ditch the lid.  The reason is if you are using filtered water then many people heat up the water to the point of seeing “frog eyes” and turn the stove off to save fuel (maybe a g per boil).  It’s easier to see without a lid.  My 2 cents.

[Chris R]

“If you like statistics, and have Excel, you can run a t-test to see if there is a difference between the means.”

Sample size is probably too small and the data doesn’t look like it’s normally distributed, probably better off just ranking them and using a Mann-Whitney test.

[David Thomas]

Seeing into the pot and stopping the flame as you exceed 160F would easily save more fuel than the small evaporative losses the lid avoids.  Why make 200F hot chocolate or soup when you’ll then spend minutes blowing on it to cool it off again?

A very thin lid of transparent aluminum would achieve both purposes at once.  

[Jerry Adams]

actually, you can hear it when it goes above 160F.  Very distinct increase.  You don’t need to see it.  Even more distinct at 170F.

I like the idea of using excel to calculate statistical functions.   In my case maybe I got one good pair of lid/no lid data.  You can only calculate the mean : )

[David D]

Its nice to visually know when 195F is reached as well.  For freezer bag cooking, water in contact with plastic bag should stay below 195F (info from sous vide cooking). Max temp varies with contact time, but this works for typical cook times of a couscous meal.

The Flash pot has a clear lid.  For specific trip durations, the weight increase of the pot can be more than compensated by being to use a smaller canister

[jscott]

 

I bet Jerry loves Freakenomics radio!

And how was the environment in general? It takes longer to achieve a boil at altitude. Did you boil at sea level, etc.??? What was the starting temp of the water? Would your findings hold for water taken from a really cold mountain stream at altitude? I would imagine if the ambient air temperature was 40 degrees, it would take longer to boil water. Did you boil in late summer, 80 degrees outdoors, with water from a warmish mountain lake? Of course, a breeze greatly impacts the performance of a stove without a windscreen. You mentioned winds, but how much of the boil time was affected by winds on the water (isn’t that a song?) as opposed to the flame. We don’t know!

in short, I remain skeptical of the gear skeptic for sure. I applaud Jerry but there are so many variables here left unanswered.

By the way, it’s pretty simple to lift a lid off a pot to see if the water is bubbling. If that’s too much effort and is a reason to leave a titanium lid home…well…

I’m with the home cooks who use a lid to boil water.

[Alan W]

A lid has mass and heats up, and it will thus absorb fuel energy. Necessarily, a lid is an additive portion of fuel load.

A lid also reduces energy loss from the system (flame/pot/water/headspace/optional lid) by reducing convective heat loss from headspace above the water.  A further factor in this is that the humidity in the headspace affects the rate of evaporation from water surface, and a lid raises headdpace humidity reducing evaporation, especially before vigorous boiling.

Thus, some effects of lid (its mass) hurt and some help (reduced convective loss from headspace). Balance will depend on actual lid, water level in pot, and actual wind.

Complex.

I, too, am surprised net effect of lid is small at low wind in these experiments.

However, believe the data. Question the experiment, including measurement methods and the variables contolled/uncontrolled. Question the mental model and analysis.

≈===========

The bubbling behavior is a function of pressure, read altitude, and not just temperature.

I often camp near treeline in Rockies, and boiling temperature there is only 190F.

I camp at many different altitudes and do not trust my visual-mental calibration of Pasteurization Bubbling vs Altitude.

When “cooking” with untreated water, I go at least to rapid,  vigorous bubbling, though not rolling boil. Risk-reward. Gram smart or gram stupid.

[jscott]

I laughed at the notion of pasteurized water, but everyone else took it in stride. Maybe if I were camping around cows…? Kidding! I get it. You scientists can be inadvertently funny to the rest of us, or maybe just me. Water doesn’t moo.

[MJ H]

I’m not a scientist, but I’m pretty sure that pasteurization is heat treating (below boiling) to kill germs regardless of what you treat. The reason we think of pasteurization as something done to milk is because if you boil milk, it doesn’t taste like milk afterward, so you pasteurize it.

[jscott]

yep, MJH, I understand that. I’ve never heard the term ‘pasteurized water’ before. Maybe I live under a rock. I was amused.

[David Thomas]

How to use boiling water and a thermometer as an altimeter:

[Brian H]

That is a really cool graph, thanks for sharing!  Sometimes I put way too much trust in my Fenix 3.

[Steve S]

A low conductivity lid might save fuel and time — particularly in a breeze.

[David D]

Are there any figures of merit for boil time vs altitude?

The results in the BPL article testing pots and stove boil times (where the Flash pot saved 40% fuel)  all showed fuel consumption numbers much higher than I experience in the field or other controlled tests published on line find, even after factoring in temperature and wind.

I always wondered if the cause was BPL testing at higher altitudes.

[Dan]

nm

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