While anyone following this nutritional series might already be aware of the pressure cooker’s amazing nutritional conservation and magnification prowess there is a little something extra that the pressure cooker can do and it’s pretty exciting.
tomatoes & eggplant
Researchers in India, tested eight techniques for washing tomatoes including cooking under pressure, to find out which was best for removing pesticide residue.
The techniques they tried were: washing under tap water; a 10-minute soak in a 2% salt solution; 10-minute soak in a 2% tamarind solution (comprised of tartaric acid); 10-minute soak in lemon water; 10-minute soak in 0.1% Sodium Bicarbonate (baking soda) solution ; dipping the fruits for a minute in 4% Acetic acid (vinegar) solution; dipping the fruits in a formula that combined some of the previous methods (vinegar, baking soda lemon); 10-minute soak in commercial “Bio Wash” solution; and pressure cooking.
Out of all treatments, dipping in 2% salt solution for 10 minutes is very effective in removing 45%, 43%, 52%, 50%, 54%, 48% and 76% of dimethoate, chlorpyriphos, quinalphos, profenophos, phosalone, -cyhalothrin and malathion, respectively, and [pressure] cooking removed insecticides in the range 55-80%. Dipping fruits and vegetables in 2% salt solution for 15 minutes is the best household method for removal of pesticide residues, and also the method is effective in reducing the
residues below MRL (Maximum Residue Limits). 1
While the salty soak was the easiest to do, the pressure cooker actually performed better than any other method. The study’s data clearly show that pressure cooking out-paced or matched the residue reduction the salt rinse for five of the seven tested pesticides.
Percentage of Pesticide Residue Reduction In Veggies
2% salt solution
2% salt solution
** Shashi BV et al.; Sch J Agric Vet Sci 2015; 2(1A):27-30.
While the tomato study only published the results of pressure cooking tomatoes, without sharing any data to what would happen when the tomato is just conventionally boiled, the same lab did earlier experiments with Eggplant which includes “direct cooking.” Unfortunately, the paper does not describe in detail what that means (perhaps it was pan frying) but it did show that “direct cooking” also did not reduce pesticide residue as much as pressure cooking . 2
So…could a cook achieve the same results with plain boiling or steaming without using any pressure?
Well, thankfully, a study that measured pesticide residue in cauliflower compared not only the pressure cooked but also boiled and microwaved florets. A chart from the study clearly illustrates that both rinsing and pressure cooking florets gave the optimal results. So don’t skimp on washing veggies just because they’re going to be pressure cooked, later.
As the excerpted chart shows, although the pesticide residue reduction from pressure cooking is quite high, there are two other methods that performed similarly. Those two columns illustrate the results of rinsing the veggie with sodium hydroxide and hydrochloric acid solution. Since most people don’t ordinarily know how to safely handle – much less use- lye or the main ingredient that’s in drain cleaners, the researchers recommended that the chemical treatments are best left to industrial processing. 3
Washing of [cauliflower] vegetables with water followed by pressure cooking removed maximum residues up to 70% as compared to the other processes and proved good household practice.
There isn’t too much other published to show how pesticide residue is reduced for other veggies. But I did find a couple of papers with a different finding for two veggies: pressure cooked potatoes did not reduce any more pesticide residues compared to boiling4; and, pressure cooking curry leaves only reduced pesticide residue for just one of the out of the five tested – the best method was to rinse an dip the leaves in a salt solution.5
So far, we’ve found evidence that for some veggies, pressure cooking them reduces pesticide residue. Could this also apply to meat and fish?
water buffalo & meat
Water buffalo is a cousin of the cow, under the same bovine branch in the animal kingdom. While in the western world they’re most famous for their milk products (mozzarella di buffala) in other parts of the world water buffalo are used as work animals for tilling fields and as a meat source. Due to the water buffalo’s close relation to cows, some of these findings could also apply to beef (keep reading for data on this).
The study I looked at measured residues of Cyclodiene-type pesticides in buffalo meat that was boiled, broiled, microwaved and pressure cooked6. It’s important to note that this class of pesticide has been banned for use in the United States since 19737 and severely restricted within the European Union8 but is still being used in Australia9 (the largest beef importer into the US10) and other countries.
The researchers found …
Among the cooking methods, pressure cooking was most effective in reducing both α- and β-endosulfan.6
Percentage of Pesticide Residue Reduction In Meat
An ambitious thesis of a budding veterinarian in India published last year measured pesticide residue reduction of ten pesticides when boiling, pressure cooking and microwaving local beef, lamb, pork, and chicken. The data was collected by testing 30 samples of each food item and the results are illuminating. Pressure cooking the meats outperformed microwaving and boiling. All pesticides measured were reduced the most with pressure cooking in pork, lamb, and chicken while for beef nine of the ten pesticides measured were reduced.11
But, a published paper, found that grilling lamb, compared to roasted and pressure cooked12. And freshwater fish doesn’t seem to get any additional pesticide reducing benefits from pressure cooking, either – faring better with baking13 and frying14.
what’s going on?!?
Actually, no paper or thesis referenced for writing this article actually spelled out why pressure cooking some vegetables can reduce their pesticide residue. But, since pesticides are made with volatile compounds that sensitive to high temperatures, the theory so far is that the higher temperatures of the pressure cooker (at least for some foods) accelerates the degradation of the pesticide to the point where it is more difficult to detect.
Although there are still more questions and than answers on this topic, this new pressure cooker super-power was worth sharing because although everyone wants to purchase and eat high-quality foods, at the moment bio/organic foods cannot be priced for every budget.
See Also: Pressure Cooker Nutritional Information