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I found a polypropylene (♷) measuring cup in my home today, of the sort that comes with an immersion blender for preparing drinks. Printed on it is the warning "not to be used with hot or carbonated products". Hot I understand: the heat can warp the plastic, or cause chemicals to leach therefrom into the food. But why not use it with carbonated liquids?

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As identified in my original comment, the most likely risk is not from the container itself, but from the fact that it's meant to be used with an immersion blender.

Heat actually isn't a major problem with polypropylene (PP). It's generally regarded as food-safe and is BPA-free (see here and here for references), and its melting point is somewhere between 130°C (266°F) and 171°C (340°F) depending on its specific crystalline configuration (or isotacticity). So you could even pour boiling water into a PP container without major risk of deformation - just don't try to bake a casserole in it or anything.

PP is often injection-molded, which can leave molding seams; these could be weak points in a closed vessel containing a carbonated beverage. But that's not really a concern with an open container.

Once you introduce an immersion blender with fast-moving blades, though, you've got the potential for hot liquids to be flung outwards if not fully submerged, causing possible risk for burns. Those blades will also intensely agitate carbonated beverages, causing a release of CO2 and extensive fizzing. The biggest reason not to use an immersion blender with these is probably that you'll lose half of the volume to spillage, and agitate the rest to the point of losing its carbonation.

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The problem with carbonated liquids is cavitation.

In normal water, if you spin up a propellor fast enough, you'll cause the disolved gasses to come out; this causes dramatic wear on the blades/fins, and in some cases, can cause fatigue resulting in them tearing off. This is actually a major issue in pump and boat propellor design.

If you're dealing with carbonated water, the bubbles form at all speeds. I doubt you'd do much damage to the blades (although you'll likely cause the same mess as with hot liquids, but at high speeds you'd run that same risk of damage and fatiguing of metals ... after doing it enough, the blades may break off while rotating and lead to injury.

(and this makes me wonder -- are there issues with using blenders at high altitutes?)

  • Adding to this answer - think of cavitation in terms of the blade entering water (which is denser) then exiting into air (which is less dense) then entering into water again (which is denser). This repeated process at high speeds puts immense strain on the blades to the point where some failures will launch the blades. Also - I haven't heard of any issues with using blenders at high altitude as high altitude wouldn't cause the same issue as bubble caused cavitation. – jsanc623 Jul 18 '14 at 17:26
  • I didn't know that cavitation is so bad. Does it mean that my high speed blender will fail quickly, or at least require a new blade? It causes cavitation all the time. Is it a thing the owners of high speed blenders have to live with? – rumtscho Jul 18 '14 at 17:55
  • @rumtscho : I'd assume they'd be rated for the typical operating speeds; also, most bar blenders have much heavier duty blades than immersion blenders. – Joe Jul 19 '14 at 0:36

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