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Cooking in Pressure Cookers
Dr. KS Raghavan Bookmark and Share

Cooking time is an important parameter in any food preparation. It has got to be optimum as the cooked ingredients have got to be just soft enough for chewing. Overcooking leads to loss of nutrition and taste. When one cooks in open vessels it is easy to get the right time through observation and it is simple to attain the right softness and also the right consistency. Difficulty arises, however, when it comes to the question of pressure cookers.
A practice widely followed in India is to count the whistles. There is a predetermined number of whistles to be counted depending on the contents being cooked. Many recipe books and web sites devoted to cooking do recommend this practice.
However this practice is unscientific, unreliable and uneconomical due to the reasons mentioned below.

UNSCIENTIFIC: The principle of pressure cooking is to maintain a temperature of about 120 degrees inside the cooker as opposed to a temperature of 100 degrees attained in open vessels. This temperature will greatly reduce the cooking time. The weight is designed in such a way that it will kick when the pressure inside just exceeds one atmosphere gauge thereby releasing the excess pressure. This is the pressure at which the boiling point of water is 120 deg. C. The first whistle is the indication that the requisite pressure and temperature have been attained. At this stage it is only necessary to maintain these conditions and this can be done by bringing the flame to low heat just sufficient to have hissing sound (indicative of slow steam release) from the cooker. The cooking time has to be reckoned from this instant.
If the flame is not reduced, more heat is input to the cooker and consequently more steam is generated and the heat input goes in as latent heat and hence the temperature remains same, which is 120 degrees.

UNRELIABLE: The weight of the pressure cooker kicks every time the pressure inside just crosses a threshold value just above the preset limit of 1 atmosphere. This does not happen if the flame is kept at low heat. At higher heat inputs more steam gets generated and more frequently the threshold value is crossed. The frequency at which this happens, however, is directly dependent on the rate of heat input. More the heat, higher is the frequency and hence lesser is the time for a given number of whistles and consequently less is the cooking time.

UNECONOMICAL: As already noted, the temperature inside cannot be brought much above the limit of 120 degrees. If the weight gets stuck and does not kick, the safety valve comes into play to prevent pressure or temperature reaching dangerous levels. The temperature level is all important for cooking and if the flame is kept higher than optimum, we are wasting heat energy without any gain.

The right approach: After setting the cooker bring the gas to high flame and maintain this level till the first whistle. Bring the gas to low heat and start a stop watch which is preset to the requisite time. This time depends on the contents (About 4-5 minutes for rice, 6-7 minutes for dal, about 12 minutes for chole etc.,.). Ensure that there is continuous slow steam release – hissing sound). After the preset tim switch off the gas.


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02/25/2013
More by : Dr. KS Raghavan
Views: 4253      Comments: 5

Comments on this Blog

Comment Sir, but isn't it that pressure cooker works on PV=nRT.
Then obviously pressure is directly proportional to the temperature.So any reduction in temperature should surely result in decrease in pressure.

nipun
04/16/2021 04:46 AM

Comment Manjula, I am surprised that my article which is almost 8 years old is getting attention. I am also surprised that Prestige user manual is making mention of whistle counting.

There is no scope for any confusion. What I have written in the blog article is one hundred per cent correct. It is fool proof and I would advice you stick to it. Of late I am using induction cooktop. Once the pressure is reached I set the power at 600 watts. And also set the timer. Five or six minutes for rice, seven minutes for dal, fourteen minutes for chole and rajma, fifteen minutes for bengal gram are my thumb rules.

I will try to contact Prestige company in this regard.

Thanks. Happy cooking.

ksrblogs
02/07/2021 08:31 AM

Comment After going through the user manual I used my new prestige pressure cooker 36 years ago and as per the manual just after the first whistle I simmered down the flame, for 7 or 10 to 15 minutes accordingly like dal, vegetables, potatoes, pulses, rice whether they are cooked together in different vessels at the same time or cooked as a single item or directly cooked items like pulav, bisibele bath, ven pongal, vangi bath etc.

I purchased a new prestige pressure Cooker today(6:2:2021) in exchange of the old one. In the user manual it is mentioned that we need to take 3 to 4 whistles. I am confused now. Which is the real cooking time? Number of whistles or lowered flame time just after one whistle?

Manjula M
02/06/2021 08:13 AM

Comment Vapor cooking is different from pressure cooking. In a pressure cooker one cannot remove the lid till the pressure inside becomes atmospheric. In pressure cookers one often keeps more than one item, for example rice and dal. As dal takes more time to cook it is possible that rice can get overcooked. Ofte this may not happen because of the right amount of water used with rice. But if vegetables are cooked along with dal, the former definitely gets overcooked and is not recommended from nutrition point of view. My practice is to cook vegetables in a microwave oven and dal in the pressure cooker. For making sambhar, these two ingredients are mixed later.

ksrblogs
11/03/2013 01:15 AM

Comment Tutti Quanti Vapor Pressure Cooking© The title makes one think this report will solve all the problems relating to the matter, but what it does is try and explain how to choose the right cooking time interval for A SINGLE type of food when you pressure boil. So what if one vapor cooks SEVERAL things simultaneously? That's what I ALWAYS do. It can be seven, eight or more things: rice, barley, potato, carrot, tomato, cucumber, ripe plantain, radish, asparagus, pumpkin, artichoke, corn (maize)…. (I don't eat legumes because I lack the enzyme that breaks them down, but it can be bought at health-food stores.) Moreover, I NEVER boil them. It's always VAPOR cooking, which probably avoids the destruction of the vitamins. First you put some water in the pot, then you place a metallic artifact that's like a platform where you can place the food, but I add a THIRD object that will hold the juices, which is a round vessel made of thick, heat-resistant glass (cp. Pyrex). If you include a cereal you'll have to put some water in the second vessel, too. This water will evaporate partly or entirely, according to the cooking time. The cereal will dry up if the time is excessive. It's best for it to remain slightly humid. If a piece of radish is included and there's rice or barley, too, you have to place the radish in a small (maybe stainless steel) vessel within the glass vessel so that its juice won't ruin the rice with its sweet flavor (and color). The sweet juice of the ripe plantain will also ruin the cereals, so that, too, has to be isolated thus. (One can mix the rice with some grated coconut, even though the water will send some of the coconut floating around. Since the water evaporates, the coconut will eventually settle down.) Finally there's the problem of the different cooking times. A perfectionist will open the pot, take out the easily cooked things after a few minutes and then seal the pot once again and continue cooking the tougher things. I don't bother to do this anymore. The water in the pot will acquire a nice, mild, vegetably taste (cp. potlikker) and can be left to cool down and then it can be drinked for refreshment in "the pause that refreshes"©. When taking out the glass vessel some of the juice in it might drop into the water in the pot, so if you haven't isolated the radish and the plantain it will, of course, turn into sweet water. I never ever read about all of this anywhere. It's based on many years of my own experience, and I wonder whether or not anybody else does those things, or if there's a book that describes the procedures. If not then I hereby patent them and call them Tutti Quanti Vapor Pressure Cooking©. I've always wondered what would happen if I were to put a raw egg still in the shell in the pressure cooker. Would it explode? Caution and respect for food has hindered me from trying this out. A physicist would probably know the answer without having to ruin an egg. After the explosion the egg fragments might fly out and spread all over the place, like the Cosmic Egg of the crazy Big Bang Myth.

Daniel Rey M.
11/02/2013 20:33 PM




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