Pressure cooking expert Laura Pazzaglia made a “Pressure Cooker Benefits” infographic for electric pressure cookers. It’s clear and informative.  Laura also created other infographics.

Laura Pazzaglia is the creator of the popular HipPressureCooking.com, dedicated to make pressure cooking hip. She is more than a prodigious cook, writer and educator.  Laura has also devised a simple but ingenious benchmark to measure one key aspect of pressure cooker performance.  She calls it evaporation measure. In her own words, this is done as:

“Starting with a “cold cooker” (not heated from a previous test) pour exactly 1000g of water into the liner and pressure cook for 10 minutes, with natural release. Then remove the lid and shake vigorously into the base and pour the contents into a zeroed-out bowl on digital scale. Record the weight of remaining water. “

Dividing the missing water amount over the total gives you evaporation rate.  It’s a straight forward measure of leakage of a pressure cooker, which works for both electric and stove-top pressure cookers, probably for stock pots too.

Why is evaporation rate important?   In “Modernist Cuisine” (so far the most comprehensive and authentic  book on the art and science of cooking), Nathan Myhrvold states that sealed cooking pots trap most aromatic volatiles which make stocks more flavourful (Volume II, pages 292). We also blogged about the astonishing discovery by Dave Arnold at the International Culinary Center that leaking steam means leaking flavour. Dave Arnold’s experiments showed that not all pressure cookers are equal in preserving flavour in stocks.  Leaky ones do a bad job, sometimes worse than a stock pot.

Hence, the evaporation rate is not just a simple leakage measure but an indicator of the quality of food the pressure cooker prepares.

What did Laura find out?

“Instant Pot only had an average 2% evaporation during ten minutes of pressure cooking (compared to Cuisinart 4% and most stove top pressure cookers 3.5%).”

In comparison, an uncovered pressure cooker at a vigorous boil for the same amount of time and same weight of water and the evaporation rate is 30%. You can read Laura’s meticulous review of the Instant Pot IP-LUX60 here.

Laura has very high standards. Instant Pot didn’t earn a perfect score. She gave IP-LUX60 a “Very Good” rating. We really appreciate Laura straight to-the-point approach and constructive criticism.  These give us something to strive to improve upon in our next model.

It’s well known that cooking rice in a pressure cooker reduces cooking time by half.  What about the cooking result? Users told us that rice cooked in Instant Pot is softer, stickier and tasted better.  We want to find out what scientists say about this.  It turns out that there are quite a few scientific research projects on this subject.  The effects of pressure cooking rice, grains and legumes can be summarized on 3 aspects.

1. Texture Change

Cooking under pressure or at higher temperature starch in rice gelatinizes to the maximum degree. This is why pressure cooked rice has a softer and stickier grain texture in comparison to boiled and steamed rice at normal pressure. Under electronic microscope, a grain of rice appears to have more pores when cooked under pressure. Please see the images between magnified 500 and 5000 times. These pores make the rice looks a bit off-white (greyish). Furthermore, tough fibers in brown rice and bran are significantly softer which give the food a better tasting texture.

Rice grain cooked under pressure. Magnified 500 times	Rice grain cooked at normal pressure. Magnified 500 times
Rice grain cooked under pressure. Magnified 5000 times	Rice grain cooked at normal temperature. Magnified 5000 times

2. Improving Digestibility and Increasing Nutritional Value

Starch gelatinization, a change of structure into a form that resembles gelatin, improves digestibility. Pressure cooking rice, grains and beans produces positive nutritional gain, from the increased digestibility of the macronutrients (protein, fiber and starch) and the increased bioavailability of the essential minerals.

Aflatoxin-producing members of Aspergillus are common and widespread in nature.

3. Eliminating Harmful Fungi and Bacteria

Rice, if not stored properly, may carry fungal poisons called aflatoxins, a potent trigger of liver cancer. A survey found that 6% of uncooked rice collected from markets in Seoul contained aflatoxins.  Conventional boiling and steaming rice at under 100°C (212°F) is not sufficient to kill all aflatoxins. Study had shown that pressure cooking at higher than 100°C (212°F) was capable of reducing aflatoxin concentrations to safe levels.

Use your pressure cooker for rice cooking.  This will make your rice taste better, more digestible and nutritious, and most importantly carcinogenic aflatoxin free.

References

• Kataria A, Chauhan BM.: “Contents and digestibility of carbohydrates of mung beans (Vigna radiata L.) as affected by domestic processing and cooking”. Plant Foods Human Nutrition . 1988;38(1):51-9.
• Leelayuthsoontorn P, Thipayarat A.  “Textural and morphological changes of Jasmine rice under various elevated cooking conditions”.  Food Chemistry, 2006, 96(4): 606-613
• Rashmi S, Urooj A. “Effect of processing on nutritionally important starch fractions in rice varieties”.  International Journal of Food Sciences and Nutrition. Jan. 2003, 54(1):27-36.
• Sagum, R., Jayashree Arcot. “Effect of domestic processing methods on the starch, non-starch polysaccharides and in vitro starch and protein digestibility of three varieties of rice with varying levels of amylose.” Food Chemistry 2000 Vol. 70 No. 1 pp. 107-111
• Eating Well: ”What is the Effect of Pressure Cooking on Nutrition?”
• Science News: “Putting the Pressure on Poisons”

Our customers ask whether electric pressure cooker is slower than stove-top pressure cooker.  Someone claimed that stove-top cooker can be 2~3 times faster in reaching working pressure.  This may be possible with a gas-stove.  However the majority of North American families use electric stoves. We decide to run a test on this typical scenario.

Test equipments:

• 

  Instant Pot IP LUX60 at the heating stage

  Instant Pot IP-LUX60: 1000W, 6L inner pot. Plugged-into an electronic power meter (Kill-A-Watt P4400).

• 

  T-Fal Safe 2 on Maytag electric range

  T-Fal Safe 2 Model 3271 stove-top pressure cooker, 6L capacity, which likely has a pressure rating of 11psi.

• Maytag SuperCapacity Plus electric range with glass ceramic cooktop, coil element power rating: 2100W
• Thermoworks Splash-Proof Super-Fast Thermapen, accuracy +/-0.4°C (0.2°F).

Test conditions:

• Fill both Instant Pot and T-Fal with 3 liter tap water at 13.6°C
• Set to cook at full pressure for 10 minutes. The “Manual” mode of Instant Pot was used.

After running multiple tests, the following is the results:

• Instant Pot IP-LUX60 took 23:30 ~ 24:15 (minutes:seconds) to reach working pressure 11.6psi.  Hold pressure for 10 minutes. Total power consumption 0.35~0.36 KWH.
• T-Fal on Maytag electric range took 24:05~24:50 to reach pressure (steam release started leaking steam and rotating).  Afterwards, power was turned down to 30% to maintain the pressure. Total power consumption based on the power rating: 0.945~0.974 KWH.

In conclusion,

• The stove-top T-Fal + Maytag electric range take about 20~30 seconds longer to reach working pressure than Instant Pot IP-LUX60.
• Instant Pot IP-LUX60 uses around 63% less electricity than the T-Fal in this specific test.

There are two possible explanations regarding the electricity consumption:

1. The glass ceramic cooktop reduces heating efficiency. The whole stove was warm and the T-Fal radiated heat along the way. That’s where the energy had gone.
2. 

   Curved 3-ply bottom of Instant Pot stainless steel cooking pot

   Instant Pot has two layers of air insulation, which minimize energy leakage. The bottom of its inner pot is curved inwards which fits tightly on the heating element curved outwards. Thermal conduction is excellent.

When we first designed Instant Pot, the intention is to make it fast in terms of convenience.  A press-a-button set-and-forget smart cooker is our objective.   Now heating efficiency makes Instant Pot faster than stove-tops on an electric range.