2

I care about gas saving and for that I want to cook with the lid covering the pot. This allows me to reduce the fire power of the stove top (then using less gas).

I need to cook foods in cooking pots such as rice, noodle, etc. Everyone that cooks these foods know they tend to overflow and (also look at this for the why) if the lid is over, except if the fire is really low, (wich is indeed a possible solution to my problem, but read below).

Idea 1: Is there some ingredient (like salt) that reduces a lot the bubbles that overflow and doesn't affect compromise the food?

Idea 2 (I want this one): Is there a device that releases the pressure automatically when the pot is trying to overflow?

Edit clarification: It's unfortunate that I referred to the pressure associated with the heating boiling food inside the pot (wich is extremely small, but still enought to lift the lid (Is it or I'm wrong?) and pressure cookers in the same post, wich have a HUGE pressure. This realization is important for me!

PD: Are we sure that my idea of releasing vapour periodically doesn't save more than just open? To me is not so cutting obvious, it needs a proof (sorry if it's basic thermodinamics, I'm ignorant on that).

PD2: This got all really good answers! I hope you don't get put off that Im not accepting right away, but I can tell you the discussion was very good!.

Is this device what I'm looking?

  • 1
    Pedantic note (sorry): there's not really very significant pressure under the lid of a normal pot, it's mostly just that the lid holds the hot air and steam in. This does kind of matter for your question, since it makes it clear that you're not looking for anything fancy, just for hot air to leave the pot. – Cascabel Jun 20 '16 at 15:58
  • @Jefromi That hot air and steam I'm calling pressure in the sense more force than the air external pressure, and sufficient to lift the covering lid to overflow. Probably my definition of pressure is a little loose. I know that the pressure is very small! But it's still bigger than the atmosphere one. – Santropedro Jun 20 '16 at 16:29
  • Sure, it's pressure, just saying it's not significant - for example it would only take 0.0006 atm to lift a 12", 1 lb lid. So you're not talking about controlled release of pressure (you don't need valves or anything), you're just talking about hot gas, which will safely leave the pot if there's an opening. – Cascabel Jun 20 '16 at 17:04
4

The device which "releases the pressure automatically" is a normal pot. You don't put the lid fully on, you leave a small gap on the side. It is sufficient for practically all cooking.

And yes, if it is still overflowing, you should reduce your temperature. Not only don't you win anything by cooking it at such a high flame that it boils over even with a gap, you are also wasting gas - which you said you care about.

As for the device you linked, it is a very different thing. It cooks food faster because at higher pressures, it can be heated to over 100 Celsius. Cooking with it is very different from cooking with a normal pot, and it is up to you if you want to get into it - but not having to leave the air gap is not a typical reason for it.


Trying to clear this thing up after some discussion with Jefromi:

You are pumping more energy into the system than it can hold. You have a few possible solutions:

  1. Stop pumping that much energy into it (reduce the heat). It is wasted anyway.
  2. Have an open system - one which can't withstand pressure and bleeds it off as soon as it starts rising. This is the "pot with a gap in the lid" method, no matter if you are using a standard lid or one with the gap and catch lip built in like suggested in the other answer.
  3. Have a closed system which can keep in the energy (it will produce pressure higher than atmospheric pressure) and release it after you are done cooking. This is what a real pressure cooker is for. It does come with some advantages, I've also seen claims that it is more energy efficient (I don't know if it is, really), but it is really a completely different mode of cooking.

What you are proposing is a mixture of 2 and 3. Now, if you make it very close to 2, such that minute amounts of pressure are built up before venting, you are still expelling that same energy from the system, and haven't saved it in any way. You just have created a more complex (and so more expensive less failsafe) device, there is no reason to not stay with solution 2. If you make it very close to 3, in that you hold in a lot of pressure before releasing, you automatically make it almost the same as pressure cooking, only with some useless venting of energy, so there is no reason to not build a real pressure cooker. Basically, anything in between 2 and 3 is going to be worse than both 2 and 3.

The most practical solution, used by countless cooks over the world, is a combination of 1 and 2.

  • 1
    Hi! This is just a comment to add a quick opinion to this well-written answer. I too find that leaving a gap open in the lid is very effective. In addition, I watch and adjust it as I go along. Usually in the beginning the pot needs a decent-sized "air hole" to keep the liquid from boiling over. As it evaporates, or cooks into your food, there's less liquid left to boil over, so fully covering the pot at that point becomes possible, and can help save gas. – Sue Jun 20 '16 at 15:07
  • But if you leave a small gap constantly open you can cause heat to escape and loose heat. I was thinking of a valve that releases the pressure periodically every minute or so when it tries to overflow, in a covered lid set up. I don't know if my setup doesn't waste more energy than yours. – Santropedro Jun 20 '16 at 16:32
  • OK, if you want pressure to build up, you are really talking about pressure cooking, and you need the device and the recipes for it. I thought you are just talking about normal cooking without any pressure. – rumtscho Jun 20 '16 at 16:45
  • @rumtscho Pretty sure not pressure cooking - a pressure cooker can't overflow! The OP is just referring to the teeny pressure of hot air/steam under a lid. (see also comments on the question) – Cascabel Jun 20 '16 at 17:23
  • @Santropedro I don't really see much difference between continuously venting a little bit of heat/steam and periodically venting a larger amount. The whole goal here is to vent enough heat/steam to prevent overflow; if you're worried about wasting energy, turn the burner down. – Cascabel Jun 20 '16 at 17:24
2

There are devices sold for this purpose which use two concentric lids, like https://www.amazon.com/Boil-Over-Safeguard-Silicone-Spillovers/dp/B00BPYTPJC.

Mind that some things will boil over even in a wide open pot, you would have to experiment whether such a device will help in these conditions.

1

As stated in the linked question a little oil will help.

A taller pot, lower the temperature, and monitor.

With a noodle that you are going to drain more water will be less foam. But more water is more water to heat.

For rice consider an electric rice cooker.

Based on your comments about pressure you don't understand the mechanism.

With or without a lid once it starts to boil with the starch it will foam. With a lid you hold in heat so it will boil with less heat. If you remove the lid and it suddenly stops foaming it is because it is no longer boiling - heat escaped.

The lid does not have a perfect seal and even if it did even a 1 lb lid on a decent size pot is 0.01 PSI. Atmospheric pressure is 14.7 PSI. The lid has no appreciable effect on pressure. I just holds in heat which raises the temperature.

OK I will try the mechanics one more time. This is not really thermodynamics. It is heat transfer. There is no appreciable difference in pressure.

With no lid you have the following heat loss:

  • sides

    • conduction
    • radiation
  • top

    • evaporation
    • conduction
    • radiation

Evaporation at simmer or even a slow boil is the major heat loss.

With a lid you cut the heat loss out the top easily in 1/2. You cut total heat loss by 1/3. If it is simmering with the lid off then you need to reduce the heat by like 1/3 when you put the lid on. Imagine heating your house with the door open or the door closed.

Another factor is you don't see it. With the lid off you notice early. With the lid on you don't see it until it is at a full foaming boil. Go with a low heat. You don't have to boil to make noodles or rice.

  • About I don;t understand the pressure, ok I'm sure I don't, but I think the imbalance matters. There is atmospheric pressure inside the pot also, so that should cancel the external and the remaining pressure of the lid should matter a little, fighting against the pressure of the boiling rice? Of course, I admit, I don't know about this things, just wanted to clarify my perspective. – Santropedro Jun 20 '16 at 18:43
  • I have a degree in chemical engineering. The pressure with a lid is not even 0.1% higher. Not even 1/1000. A pressure cooker is a different beast with a seal and a lock. – paparazzo Jun 20 '16 at 18:45
  • Read the edited post, and yes It seems you have a degree! – Santropedro Jun 20 '16 at 19:02
  • A glass lid can help with that last factor - you can see what's happening without opening the pot. – Ecnerwal Jun 21 '16 at 2:54

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