The practical effect of thermodynamics on eggs
Discussion
Unfortunately my mathematical learning curve peaked just before I got to this subject (thermodynamics not eggs). So here's a question for those whose curve didn't...
Firstly, we know that air becomes less dense as it gets hotter. That should mean that the pressure is lower. But according to my barometer, 'sunny' is marked with more inches of mercury suggesting the opposite. That's the first conundrum I hit while posing the second question, the answer to which may now be the opposite of what I thought...
Today I had soft boiled eggs for lunch. 4 mins. However this proved slightly too short to cook all the white. How much longer (or shorter!) would it take to cook eggs to the same extent if the air temperature was not 25C but 10C?
Firstly, we know that air becomes less dense as it gets hotter. That should mean that the pressure is lower. But according to my barometer, 'sunny' is marked with more inches of mercury suggesting the opposite. That's the first conundrum I hit while posing the second question, the answer to which may now be the opposite of what I thought...
Today I had soft boiled eggs for lunch. 4 mins. However this proved slightly too short to cook all the white. How much longer (or shorter!) would it take to cook eggs to the same extent if the air temperature was not 25C but 10C?
There are two separate answers.
It is sunnier and therefore hotter when the pressure is high as the higher pressure air can hold more water vapour before it condenses and forms clouds, also the air in high pressure areas is descending so the air is moving from lower pressure at altitude to higher pressure low down so the pressure increases keeping the water vapour from condensing. Amount of clouds and sun dictates the temperature.
The temp of boiling water is dependent on air pressure, but the difference in boiling point caused by air pressure you see in one place due to the weather is negligible. Unlike if you go up a mountain where boiling point is much reduced. Where I live in Switzerland at 250m above sea level the boiling point is about 98 degrees so barely affects time to cook an egg. If the external air temp is lower it would take a small amount of extra time to bring the water to the boil, but if the egg is put in once the water is boiling there would be less difference than caused by the size of the eggs as bigger eggs take longer to heat up.
It is sunnier and therefore hotter when the pressure is high as the higher pressure air can hold more water vapour before it condenses and forms clouds, also the air in high pressure areas is descending so the air is moving from lower pressure at altitude to higher pressure low down so the pressure increases keeping the water vapour from condensing. Amount of clouds and sun dictates the temperature.
The temp of boiling water is dependent on air pressure, but the difference in boiling point caused by air pressure you see in one place due to the weather is negligible. Unlike if you go up a mountain where boiling point is much reduced. Where I live in Switzerland at 250m above sea level the boiling point is about 98 degrees so barely affects time to cook an egg. If the external air temp is lower it would take a small amount of extra time to bring the water to the boil, but if the egg is put in once the water is boiling there would be less difference than caused by the size of the eggs as bigger eggs take longer to heat up.
otolith said:
Assuming that the eggs go from fridge (fixed temperature) to boiling water (fixed temperature) air temperature is irrelevant.
But air pressure affects boiling point - the lower the pressure the longer the eggs will take to cook because the BP is <100C. I agree it's negligible, but I was hoping someone could work it out in fractions of a second 
I believe on Everest the boiling point of water is sufficiently ow due to low airpressure (c30% sea level) that you cannot safely boil an egg (vague recollection from thermo lecture many years ago.. but no actual source). I think water boils c 70degC at the top of everest.
But pressure variations due to most weather changes are fairly small in the grand scheme of things.. so if you are at or near sea level i wouldn't expect to sea massive variations in boil times.
Now if you were in the eye of the worlds largest megacyclone (a la " Day after tomorrow") then maybe atmospheric pressure would drop sufficiently to cause a difference.. ...but I suspect you would wider worries on your mind at that point..
But pressure variations due to most weather changes are fairly small in the grand scheme of things.. so if you are at or near sea level i wouldn't expect to sea massive variations in boil times.
Now if you were in the eye of the worlds largest megacyclone (a la " Day after tomorrow") then maybe atmospheric pressure would drop sufficiently to cause a difference.. ...but I suspect you would wider worries on your mind at that point..
The difference of a few mbar (e.g. low pressure poor weather vs higher pressure good weather) is minimal.
e.g. 1020 mbar is a boiling point of 100.2°C, at 980 mbar you're looking at a bp of 99.3°C, so barely any real difference, and it'll be overwhelmed by other effects like ambient room temperature.
e.g. 1020 mbar is a boiling point of 100.2°C, at 980 mbar you're looking at a bp of 99.3°C, so barely any real difference, and it'll be overwhelmed by other effects like ambient room temperature.
IJWS15 said:
How big is (was) the egg?
Ah yes, the missing variable! I can't supply an exact volume so could you insert 'medium' into your calculations?Krikkit said:
The difference of a few mbar (e.g. low pressure poor weather vs higher pressure good weather) is minimal.
e.g. 1020 mbar is a boiling point of 100.2°C, at 980 mbar you're looking at a bp of 99.3°C, so barely any real difference, and it'll be overwhelmed by other effects like ambient room temperature.
Now we're getting close... The room temp is the same as the outdoor temp as the doors are open. Say 24C.e.g. 1020 mbar is a boiling point of 100.2°C, at 980 mbar you're looking at a bp of 99.3°C, so barely any real difference, and it'll be overwhelmed by other effects like ambient room temperature.
otolith said:
Interesting.In the USA, eggs are refrigerated because the US Department of Agriculture requires eggs sold for consumption to be washed, processed, and then refrigerated before they come anywhere near a store’s (chilled) shelves. On the other hand, most European and Asian countries have reached the opposite conclusion, requiring that table eggs not be wet-washed, and also not refrigerated.
Eggs only need refrigerating if they've been washed - washing removes their natural protective coating (the cuticle) which has natural anti-bacterial properties. They of course *can* be refrigerated - but then you're putting unwashed eggs in your fridge, which for me is a bad idea for potential spread of nasties. Instead I keep them in a cool, dry place, and if I feel the need wash the eggs I plan to use immediately before use.
That also allows me to float-test eggs (use by dates are daft on eggs).
So, out of interest, did those Asda eggs come from a chilled display or an open shelf? My understanding of UK egg-labelling was they were meant to be marked "keep eggs refrigerated or store in a cool dry place" - your Asda eggs are missing the second part of that.
A bit more and links: https://gizmodo.com/why-the-british-dont-refrigera...
skwdenyer said:
Eggs only need refrigerating if they've been washed - washing removes their natural protective coating
This is all valuable information in my quest. The cuticle will affect the thermodynamic properties!So I need to amend my question as follows:
'Today I had soft boiled eggs for lunch. 4 mins. However this proved slightly too short to cook all the white. How much longer (or shorter!) would it take to cook washed eggs to the same extent if the air temperature was not 25C but 10C?'
Simpo Two said:
skwdenyer said:
Eggs only need refrigerating if they've been washed - washing removes their natural protective coating
This is all valuable information in my quest. The cuticle will affect the thermodynamic properties!So I need to amend my question as follows:
'Today I had soft boiled eggs for lunch. 4 mins. However this proved slightly too short to cook all the white. How much longer (or shorter!) would it take to cook washed eggs to the same extent if the air temperature was not 25C but 10C?'
Gassing Station | Science! | Top of Page | What's New | My Stuff