Physics/Chemistry Help

[RazorCatchPrey]

Ok, who can explain the principles at play here with this screw-up on my part so I can dazzle my wife with the scientific explanation when she asks me what the hell happened to our kitchen?

I was taking a short cut in making a yeast starter by putting my erlenmyer flask with DME and water directly in the microwave to boil. As soon as the buzzer went off (it had been boiling for a good three minutes) I used a pot-holder and took it out. Figuring to make sure everything was good and mixed, I gave it a quick little swirl.

Well, when the boiling wort touched the sides of the flask above where the line had been, it erupted. I am talking a full out wort geyser all over the kitchen. And y'all know how sticky DME wort is. My stove, oven, microwave, counter, crock pot, floor, and cabinets are now covered in it. Not to mention myself.

Luckily I only received very minor burns to my hand in the process.

So can somebody explain the principles at work that created this little disaster?

 

[passedpawn]

Read up on Nucleation sites related to boiling. Microscopically-small crevices cause a pressure drop at the molecular level and thus reduce the boiling point. The liquid is at the threshold already, so when this happens you get instant boil at those nucleation sites. The exact same effect causes CO2 to come out of solution (ever wonder why there is a stream of bubbles rising in a glass from specific spot at the bottom? It's a nucleation site causing a pressure drop.) I think these sites are very small and necessarily related to the size of the water molecule. I'm no chemist or physicist, so I only have a very superficial understanding of this phenomenon.

Nucleation in boiling can occur in the bulk liquid if the pressure is reduced so that the liquid becomes superheated with respect to the pressure-dependent boiling point. More often nucleation occurs on the heating surface, at nucleation sites. Typically, nucleation sites are tiny crevices where free gas-liquid surface is maintained or spots on the heating surface with lower wetting properties. Substantial superheating of a liquid can be achieved after the liquid is de-gassed and if the heating surfaces are clean, smooth and made of materials well wetted by the liquid.

http://en.wikipedia.org/wiki/Nucleation

 

[Brulosopher]

Tip 1: Never, ever, ever make a starter that way, stoves are safer, though can produce the same geyser effect, hence...

Tip 2: FermCap S!!!!!!!!!!!

Good luck explaining this to your wife, pal. Yikes

 

[Whattawort]

Did you observe actual boiling in the flask? If not, then you may have had some superheating and when you disturbed the surface tension of the liquid it released an explosion of vapor thus resulting in your wortcano. I've only seen it happen with water in the microwave, but it's plausible that the wort and water homogenized. Or I could be full of hot wort myself.

 

[boscobeans]

Super heated water is very unstable and can expand to 3 times its volume in an instant once it is triggered. Rare to happen if something is in the water to start? But dangerous in any case.

bosco

 

[Whattawort]

Distilled water + smooth glass + microwave + metal spoon = FUN (and dangerous) science lesson! That said, it's all about the disturbance of a hot liquid's surface tension. Gotta keep it under control. Kinda like a hop addition in boiling wort. Keep your hands on the burner controls and anticipate an imminent potential boil over. You just introduced cold objects that disperse quickly (and are highly acidic) into a mostly homogenized boiling liquid that is more on the alkaline side. SCIENCE!

 

[PhillyMike]

If you ever want to do that again, or anything where you heat a liquid in the microwave, be sure to add something like a straw or wooden stirrer to make sure that your liquid does not explode again.

 

[Leithoa]

Narrow/conical vessels amplify the geyser effect discussed in the above explanations. A wide mouth vessel(beaker, coffee mug, etc) would still have flash boiled but it likely would have just calmly overflowed burning your hand and coating the floor.

 

[boscobeans]

This might be an eye opener to some.



Wear your safety glasses for this one.

bosco

 

[daksin]

You superheated your water. Smooth vessel (erlenmeyer) plus clean water plus tons of heat and no motion (microwave) equals water that is HOTTER than boiling point, but not boiling. Add any agitation or nucleation sites to that and it will immediately boil, extremely violently, and shoot out the top of your flask because it's shaped like a rocket engine.

 

[cosmo]

You guys are all so close. You boiled the water in the microwave. As the steam was coming out the neck of the flask, it became superheated while the microwave was still running. The water was not superheated, just the steam. The water could not have been heated significantly above 212F since it was not under pressure. The steam however can be heated by the microwave energy much higher than 212F. The steam heated the neck of the flask above 212F by convection and conduction. When you stirred the water, the vortex went slightly up the side of the flask. With the water at about 212F coming in contact with the neck of the flask at a higher temperature, the water instantly started to boil. FWIW this is the same phenomenon that can cause severe burns when lifting a lid off of something you just take out of the microwave. The steam is superheated and can get much hotter than 212F. Surface tension can also be a factor, but I think in this case it may not be the driving one.

 

[donchan1]

Daksin is correct. Here is a good description:
http://en.wikipedia.org/wiki/Superheating

If it was just the solution coming in contact with the superheated neck of the vessel, only the portion of the solution in contact with that surface would boil, and you would not get the geyser described by the OP.

 

[mbobhat]

Yea this can happen when you got some wierd liquids in solution sometimes in the lab, when it doesn't boil quite right and kind of shoots up in a big bubble it is called "bumping", although you had something more like an eruption. To fix, scratch the bottom of your flask a little bit with a glass rod or add a couple tiny rocks in the bottom. It'll add the sites so that it more safely boils rather than erupts.

Wort seems to do that though, whenever I am boiling extract to make a starter I always get a starchy spaghetti-like boilup and then it subsides.

 

[cosmo]

Daksin is correct. Here is a good description:
http://en.wikipedia.org/wiki/Superheating

If it was just the solution coming in contact with the superheated neck of the vessel, only the portion of the solution in contact with that surface would boil, and you would not get the geyser described by the OP.

I stand corrected. Apparently water in liquid form and steam can be superheated. Good post.

That would explain why when I drop a stir bar into a flask of wort after taking it off the burner, I sometimes get a geiser.

 

[SpeedYellow]

You can also superheat water in your flask on the stovetop. This is crucial to understand when you're calibrating your thermometer. If I just boil water in my flask, my thermometer reads around 216f. But after adding a pinch of something like chalk or pebbles, it drops to 211f.