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Measuring Yad Soledes Bo by Hand

by: Rabbi Dovid Cohen
cRc Administrative Rabbinic Coordinator
October 2007 – Updated December 2022

A popcorn company produces two types of popcorn, kettle cooked and air popped, and they produce two products on each line (kettle corn and white on the kettle line, and two variations of cheese corn on the air popped line). We’re convinced that each of the lines are dedicated for the uses noted above (see the footnote).1

There are two major differences between the lines:

    1. Seasoning… On the kettle cooked line, the kernels, salt and seasonings are put into the kettle in batches. Once the corn pops it is sent through a seed separator (to remove un-popped kernels) and then onto the vertical conveyor to go to packaging. However, on the air popped line, the kernels are air popped without any other ingredients present. Then they go through their own seed separator and fall into a tumbler where a <115° F mix of oil, cheese and seasoning is sprayed onto the popcorn, before it falls onto the aforementioned vertical conveyor to go to packaging.
    2. Temperature… The seed separating of kettle cooked products works best if the popcorn is not too hot and therefore there are cooling fans near that separator, while the separator on the air popped line doesn’t require or have any cooling.

The products flavored with cheese are not kosher; therefore the question is whether we can certify the kettle cooked products. As noted, the two lines are completely separate until the product reaches the vertical conveyor, so we can narrow the question down to whether there are b’lios into and out of the conveyor. A little probing revealed that after every cheese run, the equipment is so dirty that it must be power-washed with >200° F water,2 such that there seems to be no question that the vertical conveyor absorbs b’lios of non-kosher cheese. If so, the real issue seems to be whether the kettle cooked products are hotter than yad soledes bo (120° F) when they reach the conveyor such that they draw b’lios out of the conveyor.

How should we measure the popcorn’s temperature?

The company suggested using an infrared thermometer to measure the temperatures but we didn’t feel comfortable relying on that method because those instruments are notoriously unreliable for measuring exact temperatures as they must be carefully calibrated for emissivity and other items. Measuring with a typical temperature probe also wouldn’t work as the popcorn cools too quickly to get an accurate reading. Therefore, to measure the temperatures, we asked the Mashgiach to do as follows:

  1. Get a meat thermometer (which can be bought in most supermarkets for less than $10 and is a worthwhile investment).
  2. Mix a few samples of hot water from a kettle, and warm water from your kitchen sink, and:
      1. Measure the temperature of the different samples.
      2. Slowly pour samples that are between 100° F and 140° F onto the palm of your hand.

This exercise should give you a general idea as to what yad soledes bo / 120° F feels like on your palm.

  1. At the company, catch popcorn in your palm as it is falling onto the vertical conveyor, and record your findings as to whether it is or isn’t yad soledes bo.
  2. Repeat Step #1 at different parts of the line to try to get an understanding of when it drops below yad soledes bo.
  3. Write a report describing your findings.

Of course, in the times of Chazal, yad soledes bo was always measured with a hand/yad but in our modern age it would be fair to ask whether measuring popcorn temperature in one’s hands is the most efficient or accurate way of knowing its temperature. In this case, measuring by hand is just perfect because (a) there isn’t any other simple method to measure the temperature of a product like this which cools so rapidly and (b) we were only going to certify popcorn which we were sure is cooler than yad soledes bo under all circumstances (i.e. at all times of the year, even after the equipment has been heated by many previous batches etc.). As such, if the Mashgiach had any question as to whether the popcorn was hot, we were prepared to not proceed with certification, and his testing was merely to see if the product was surely below yad soledes bo.

P.S. The Mashgiach visited the company while they were producing both types of popcorn. He reported that the white corn (and cheese corn) products were well below yad soledes bo, while the kettle corn product was borderline. Thus, we may certify the white popcorn but not the kettle corn. It appears that the reason for the discrepancy between the white corn and kettle corn products is that the kettle corn has more caramelized sugar on its surface which helps it retain its temperature for longer.


1 The reasons why we aren’t concerned the company will interchange the use of the kosher and non-kosher lines are:
a) Air popped popcorn tastes considerably worse than kettle cooked corn, so they’d never run the kettle cooked products on the non-kosher/air-popped line. The cheese popcorn can only be made on the air popper because the cheese flavor masks the taste of the underlying popcorn.
b) The kettle poppers are batch cookers while the air popper is a continuous system. The tumbler in which the seasoning is applied, is fine-tuned to apply an equal amount of seasoning to each kernel, based on the assumption that the popcorn will continuously and consistently be fed into the tumbler, which would never work properly if they popped the corn in the batch poppers.
c) The cheese seasoning has oil in it, and a kernel that was fried in oil and then sprayed with oil would taste too oily and soggy, so the kettle popper couldn’t be used for the cheese products.

2 The good news is that since the popcorn is hydrophilic (attracted to water), they must let the equipment dry for about 24 hours after every wet wash before they can produce white or kettle corn. As such, we can be reasonably assured that the equipment will be aino ben yomo from non-kosher products, when the kosher products are run.