Adventures with mustard sauce, or the turn of two screws

Trust me, I'll get around to engineering ethics before the end of this column, but right now I'd like to tell you about my family's mustard sauce recipe. It's good on sandwiches, and here's the recipe:


2 oz. (60 ml) Colman's dry mustard
1 cup (230 ml) cider vinegar
Mix in blender - stand in refrigerator overnight.
Next day: add 1 cup brown sugar and 2 eggs.
Blend all together, cook in double boiler until thick. Stir constantly.
Keep in jar in refrigerator.

That's it. The acid in the vinegar does some interesting chemistry to the mustard, and the result is a sweet-sour flavour that is popular with several people we've shared the recipe with.

Last fall, my wife's old blender died after several decades of service, so I bought her a new one for Christmas. It is a PowerXL Boost Blender Plus, and I got it at Walmart. The other day we decided to try it out on the mustard-sauce recipe, so my wife got it out of the box and put it together. Like most blenders, it has a blending jar with thick glass walls and a big glass handle, a plastic jar base that the jar screws into (screw No. 1), and a motor assembly at the bottom that the jar base fastens into with a quarter-turn locking system (screw No. 2). I watched her put the jar base on the motor assembly, and then we mixed the mustard and vinegar and poured it into the blender. So far, so good.

The blender quickly turned the stuff inside the jar to a foamy yellowish liquid, and then we wanted to get it out of the jar. We faced a problem.

With the previous blender, the blending jar and its base would simply lift off the motor assembly, so you could carry the full jar over to a saucepan and pour out the contents. But it wasn't clear to me, nor to my wife, how you were supposed to do that with this unit. We could have lifted up the whole thing, motor and all, but it had suction cups at the bottom that held it to the counter and that didn't seem like a good idea.

Being bibliophiles, we turned to the page in the manual entitled "Using the Boost Blender Plus." Item 8 said to press the off button to stop the blender. Fine, we did that already. As far as we could tell, the relevant passage was item 9, which I quote in its entirety:


"To remove the jar, grasp the handle, turn jar counterclockwise, and lift up. NOTE: Always unplug the appliance when not in use."

Those instructions are pretty unambiguous. There's only one handle: the glass handle on the jar itself. "Counterclockwise" took a little thought, but I figured they meant as viewed from above, so I grasped the handle and gave a good half-turn counterclockwise.

A veritable Yellow River of mustard-vinegar mixture cascaded out from under the jar, over the base, the cutting board, the countertop, the cabinet, the floor, and our pants and shoes. I will not reproduce here all the things I said during this catastrophe, but they were not complimentary.

What had happened, of course, was that I had applied torque to two screws in series. Turning the jar put torque—a twisting force—on the screw holding the jar to the jar base, and also put torque on the screw-like arrangement that held the jar base to the motor assembly. When two screws are in series, the one that is less tight always unscrews first. Evidently, the makers of this infernal device designed it to be assembled by The Hulk, who would tighten the glass jar onto the jar base so tight that it would hold while the base would unscrew from the motor assembly, leaving you with the jar and its base together.

Needless to say, that didn't happen. The No. 2 screw between the jar base and the motor assembly held fast and allowed the No. 1 screw to come unscrewed from the base, releasing the flood of mustard.

Later—much later, after many paper towels and expostulations—I tried to remove the jar base from the motor assembly. The only way I could figure out how to do it without causing another flood was to hold the motor assembly with one hand and press on a projection of the base with the other hand to unlock just the No. 2 screw, without touching the blending jar. That's the only possible way to take the intact jar and base apart without spilling anything. The manual says nothing about doing it that way, but it's the only way I can see it can be done.

At first, my wife wanted to pack the whole thing up and donate it to Goodwill, but I objected that their customers hadn't done anything bad to us, so why should we do that? So we are slowly working up to considering another attempt at mustard sauce, but we will ignore anything the manual says from this point onward.

In fairness to the designers, they were trying to innovate in a legacy product (blenders). The "boost" function lets you essentially move the blades up and down while they turn, which can help with viscous mixtures, but it complicated the base to the point that it's hard to remove, and the proper way to remove the full jar with the base got lost on the way to the manual. Someday we'll get up the nerve to try the mustard-sauce recipe again, but I can't say whether we'll try this blender again -- or go to a store where they will let us take a new model apart before we buy it.

The best product in the world is useless if people don't know how to use it properly, and so this is a lesson to all designers: don't assume that the instructions supplied with the product are correct. Pretend you've never seen the thing before, follow the instructions, and see what happens. You might be in for a surprise.

Sources: The PowerXL Boost Blender Plus is distributed by HPC Brands Inc., Middleton, Wisconsin, and the product is made in China.


This article has been republished from the author's blog, Engineering Ethics.


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