Cooking times ?

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Indeed. Because of my suspicions about the oven I'm currently using, I've just taken delivery of a thermometer probe that can monitor the inside temperature, so I can find out what's really going on in there. Domestic appliances are never accurate and scientific enough for me. I had to smile when I saw how the probe can be set for pork, beef, poultry, etc. so the punters don't have to worry about using numbers. Luckily there's a manual mode.

When I repaired appliances, we were satisfied if the temperature was within 50 F of the setting, however, on the back of the thermostat, there is a little screw with a blob of white paint on it. You can break the paint and adjust the temperature to match the dial better. Or, you can re-mark the dial to match the temperature readings, which is safer for beginners.

To cook food, a certain minimum amount of energy is required for the chemical reactions to take place. This is the energy of activation in chemist’s speak. If you are cooking meat, the process involves denaturing proteins within the meat. Each cooking appliance has recommended settings, but they might not be accurate for your location. Most are measured at sea level.

Cooking times on food containers are for rough references, as they do not know what type of appliance you will be using to cook the food. Microwaves have different power ranges measured in watts. If one puts a bag of microwave popcorn into a 1100 watt microwave but uses the cooking times suggested for a 900 watt microwave, they will likely burn the popcorn to a crisp. If one does the reverse, most of the popcorn would not have popped in the time supplied.

In the case of cooking on a stove top, it becomes more of a physical chemistry problem. If one wanted to cook spaghetti, the water boils at a lower temperature at high elevations when compared to sea level. Remember, water has a heat capacity of 4.18 J/(oC.gram). That would make some think that the food would cook faster at the higher the elevation. Yet, this is wrong because the amount of energy contained in the boiling water at higher elevations is lower than the amount of energy contained in the same amount of boiling water at sea level, as it is at a higher temperature. The amount of activation energy required to cook the food is the same regardless of elevation. So, the lower elevation can give more energy (at a higher temperature) to the food particles in the same time that the higher elevation starts to cook the food (at a lower temperature).

In an extreme case, there is a limit to where boiling water can be used to cook food on a mountain top. One simply cannot cook food that way on top of Mount Everest as it is higher in elevation than that limit. The food must be prepared a different way or not cooked at all.

WP discussion thread - 'Cooking Times and the Literal Mind' is very informative:
viewtopic.php?t=379865

Rather than tamper with somebody else's cooker (and remembering the adage "never do anything for the first time"), I'm fairly content to just characterise the relationship between the temperature settings and the actual temperature.

50F seems a horrendously wide tolerance to me. No wonder I ruined a batch of paper sachets of silica gel when I used this oven to "recharge" them. The sachets went brown and brittle, which they shouldn't have done as the oven was set to just below the boiling point of water. Didn't happen the second time, though I watched more carefully then and removed them soon after they'd changed to the right colour.

[continued - split post to avoid Crapcha antics]
Hotplates are probably even worse, as disappointingly they don't seem to have actual thermostats at all, but just some cheap "energy regulator" thing that cycles between full power and nothing, with something approximating to a constant ratio between the on time and the off time for a given setting of the dial. Small wonder I have so much trouble getting the contents of a saucepan to gently simmer. One minute it's not even at boiling point, the next it's going off like Vesuvius all over the cooker, which seems designed to be hard to clean. How does anybody even begin to wrest control over such a process? I wouldn't have thought using thyristors or whatever the modern equivalent is (as per dimmer switches for lighting) would cost much in this day and age of cheap electronics. I noticed it used to be possible to buy those with pretty high current ratings, though more recently they limited them, in the UK at least. No wonder the phrase "cooking with gas" has come to mean doing something the right way.

Still, even with stable control of the power applied to the hotplate, there's still an innate problem when bringing cold food to the boil, in that how vigorously the water boils is related to the temperature of the food, which gets to its final temperature gradually. The result is that I'm having to keep watch over the saucepan and adjust the setting gradually downwards as the contents get hotter, until it's finally at equilibrium. To get round that I've resorted to first microwaving cold food such as taters, and then transferring them into a pan of boiling water when they're hot enough to minimise the aforementioned problem.

Even with that workaround, I still can't safely leave the saucepan to its own devices. Even using the same hotplate, the same setting, same saucepan, same volume of water and same weight of the same food, it can still erupt or go off the boil if I don't inspect it and adjust the dial occasionally. Why don't cookers have temperature probes as standard, to automatically control the temperature and boiling intensity of the food itself? Automatic kettles that sense when the water boils are cheap, safe and common enough, so I don't see why people tolerate anything less automatic for cooking. Or is the tedium of watching over temperamental saucepans supposed to be part of the joyful experience of cooking? Doesn't seem very creative to me, it seems more like menial labour.

All the middle-aged stoves I'm familiar with just cycle their elements on and off. You can hear the thermostats clicking. With a thick pan bottom, it isn't too bad. The old style controls with click stops used three voltages and two concentric spiral elements for steady heat, but few choices. There may be new ones with what you want, but the cheap option is to just turn a hotplate on full, and run it through a heavy - duty dimmer switch.

If you read the label carefully it says "cook for 25 minutes" or what ever amount of time but then it adds "or until cooked thoroughly. Also as has been pointed out by somebody else in this thread the label also includes the warning "cooking times may vary depending on the appliances".

I think it varies depending on the oven. I always see the times they list more as approximations. Like if it says 25 minutes, I may start to check it at 20 in case the oven is fast to make sure it doesn’t burn. If it’s not ready at the specified time, I check every few minutes until it is.
I’ve also run into this with baking if the dimensions of the pan I used are slightly different than the size listed, since this can change how deep the batter is.

Altitude also affects boiling temperature. IIRC, a "three minute egg" takes five minutes in Denver. There are variables everywhere. In winter, when the air is dry, I need to add a bit more water to the bread flour.

Yes that sounds like it could be useful. I see there's a 1000w dimmer for sale on Amazon at a fairly low price.

If I were rich, I might get something like this - a single hotplate with temperature probe and built-in magnetic stirrer to discourage sticking and precipitation. The stirrer probably wouldn't work with ferrous saucepans, and there's always the risk of accidentally leaving the stirring bar magnet in the contents and then swallowing it, which I guess is one reason why nobody sells such things for kitchen use. Like a lot of professional gear it's ludicrously expensive, and I don't see why it would cost anything like that much to make. We used to have a few cheaper versions at work but with those the magnet would often decouple its movement from the rotating magnetic field and cease to stir properly, in fact the magnet would bounce around at random in the container, which was quite annoying. Anyway, you can probably see why, having used that kind of thing in a lab, a cheap domestic cooker will never feel like it's good enough for me.
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