Boiling water is something we all do on bushwalks – whether we are making a billy of tea or heating water for dinner. So if you want to boil some water – is it better to have the lid on the billy or off? Or does it make any difference? By “better” here I am referring to the time it takes to boil.
Most people would think that having the lid on would be quicker – it traps in the heat. But is this true? Or does it matter much?
Well, I recently tried some experiments – timing how long it took to boil certain quantities of water, with the lid on and off, and using different types of billies and saucepans. I used an electric stove and all pots started off at the same temperature and were heated on the same heating element. I timed until there was a “rolling boil” – this was a bit subjective and it would have been better to repeat boiling times.
Some of my findings –
- If you are only boiling a small quantity of water (eg 400mL) then having a lid on the billy does not make much difference to the boiling time
- If you were boiling more water (eg 1200mL) – then having a lid on did make a difference – perhaps a time saving of about 10% in boiling time
- The substance the billy was made from and how thick it was did make a difference. My stainless steel billies were all slower than my thin titanium billy. I think basic physics tells us the most important factor is the heat capacity of the water rather than the thermal conductance of the billy
So for practical bushwalking these finding do not mean too much, but if you are on a trip where you are carrying a fuel stove and want to minimise fuel use – then it looks like it is better to boil water with the lid on and use a titanium billy rather than use one made from stainless steel. I did not have an aluminium billy for comparison. Other factors to consider when trying to use your fuel most efficiently would be – cook inside the tent annex sheltered from the wind, using a stiff aluminium heat shield around your stove (this also traps in heat) and not using the highest heat setting on the stove. I think studies have shown for most stoves that a lower heat setting will boil a certain quantity of water with less fuel used, although it will take longer to boil