borosilicate flask on a gas stove: any bad stories?

[kleinstadt]

So, I've got a 3L borosilicate flask and a gas stove. It takes a while for the thing to come to a boil.

I know that borosilicate flasks are supposed to be okay on a gas stove because of the even heating, the thing I'm worried about is the contact with the cast iron grates it rests on.

They're wide and thick.

I suspect they get REALLY hot after the burner has been on for a while, and I'm worried about the grates causing uneven heating, and therefore flask failure. 3L of scorched wort on the stove leads to a very unhappy SWMBO.

I've tried the alternatives; a flame tamer takes an hour to bring 3L to a boil, and I burned off the wooden handle. A double boiler never got there.

I've done the search, and found a lot of "no problems with a gas burner" responses.

While I'm interested in the "no problems with a gas burner" responses, I really want to hear of any stories of failure on a gas stove. To me, this is a bit like airplane engineering; it may work 99% of the time, but it's the 1% where it doesn't that I'm really interested in.

So, has anyone heard ANY stories of failure? Word of mouth at a homebrew club? Some other forum post from 8 years ago that you can't remember because you were half in the bag when you read it? Anything?

 

[wickman6]

Sorry, I haven't but I've wondered the same thing. I use a 2L on my gas stove too, and at times I'm a bit nervous about it.

 

[jammin]

If its quality glass, you're fine. That type of glass is used over top of Bunsen burners all the. You can boil water in plastic bottles so that tells you something about the actual temp it's getting to.

 

[pmcint01]

I've done it several times. It is very thick glass and treated so that it can be heated directly by a flame.

 

[raouliii]

I've cracked a 2L, Pyrex brand, erlenmeyer on a propane camping stove. I believe it was because of the medium flame being too hot near the outer circumference of the flask. I use a wire gauze with ceramic center under my flask now and keep the flame at minimum and heat slowly.

 

[IslandLizard]

Direct heating of glass vessels is always risky. The thicker the glass and the larger the vessel, the more time it takes to disperse the heat evenly. Most failure comes from thermal stress. The shape of the vessel plays a role too. Ball shaped flasks are more robust than flat bottomed Erlenmeyers. Although boro-silicate glass is strong, dipping a boiling hot flask in an ice bath maybe too much.

I agree on the grate parts getting hotter and may cause unwanted stress. A wire mesh with or without a ceramic center will help spread the heat more evenly.

In the labs they use electric heated, thermostatically controlled oil baths. Usually with an integrated stirrer.

 

[day_trippr]

[…]In the labs they use electric heated, thermostatically controlled oil baths. Usually with an integrated stirrer.

And thus the latest "gotta have" dyi project was born...

Cheers!

 

[kleinstadt]

If its quality glass, you're fine. That type of glass is used over top of Bunsen burners all the. You can boil water in plastic bottles so that tells you something about the actual temp it's getting to.

Yeah, but a bunsen burner is usually used with the wire gauze, which does not heat up as much as cast iron.

 

[JimRausch]

Last year I cracked a 1L Erlehmeyer by just adding boiling wort to it (the flask was cool, but I still didn't expect it). When I reported it to NB, they replaced it no problem, and kicked in a bag of DME. There were multiple reports of broken flasks around the same time.
So, never more. I boil the starter wort in a pot, cool it, then add it to my flask.

 

[jgroesbeck]

And thus the latest "gotta have" dyi project was born...

Cheers!

Now that's a funny post...

Cheers,
JG

 

[william_shakes_beer]

Last year I cracked a 1L Erlehmeyer by just adding boiling wort to it (the flask was cool, but I still didn't expect it). When I reported it to NB, they replaced it no problem, and kicked in a bag of DME. There were multiple reports of broken flasks around the same time.
So, never more. I boil the starter wort in a pot, cool it, then add it to my flask.

+1. I have a 2L e flask and only use it on the stir plate. Also it's easier to dump the yeast into a sauce pan than a flask

 

[lembeek]

I've cracked one.

I was using a long metal spoon to stir the DME into solution and left it in the flask when I put it back on the heat. A minute later a heard a pop and I found a hairline crack at the point where the bottom of the spoon met the glass. Thankfully, nothing spilled and I was able to pour the starter into another flask. I guess the heat of the metal spoon on one side of the glass and the flame on other caused it to fail.

Other than that, I've never had an issue. I always keep them on a medium-low flame.

 

[kleinstadt]

Direct heating of glass vessels is always risky. The thicker the glass and the larger the vessel, the more time it takes to disperse the heat evenly. Most failure comes from thermal stress. The shape of the vessel plays a role too. Ball shaped flasks are more robust than flat bottomed Erlenmeyers. Although boro-silicate glass is strong, dipping a boiling hot flask in an ice bath maybe too much.

I agree on the grate parts getting hotter and may cause unwanted stress. A wire mesh with or without a ceramic center will help spread the heat more evenly.

In the labs they use electric heated, thermostatically controlled oil baths. Usually with an integrated stirrer.

Sorry I've been a little absent from the thread for a few days.

I did a fair amount of organic chemistry research in undergrad, and have been dreaming about those oil baths with electric elements (and stir bars in the oil baths) for some time now. Oh, and the round-bottomed flasks. I know I missed my opportunity to get that glassware 15 years ago, so I've been focusing on what I have - Erlenmeyers.

I remember quite well using Bunsen burners, wire gauze (with ceramic), and Erlenmeyers, but I'm short-sighted enough to never consider actually purchasing the wire gauze.

Duh. I amaze myself sometimes.

I'm going to try this. Will report back if I have a problem.

In the meantime, I'm still interested in hearing anyone's horror stories about cracked borosilicate Erlenmeyers on a gas stove.

The ones so far are appreciated!

 

[MaxStout]

Watch out, as a lot of those low-cost Erlenmeyer flasks sold by brew stores and online lab suppliers are "student grade" (they tend to be lower quality with minor flaws, like scratches). Those flaws can give rise to cracks or breaks under thermal stress. Even the higher quality, lab-grade Pyrex and Kimax flasks can sometimes break from thermal shock.

The round-bottom "Florence" flasks are more suitable for boiling, though their shape isn't exactly conducive to use on kitchen stoves.

 

[kleinstadt]

Watch out, as a lot of those low-cost Erlenmeyer flasks sold by brew stores and online lab suppliers are "student grade" (they tend to be lower quality with minor flaws, like scratches). Those flaws can give rise to cracks or breaks under thermal stress. Even the higher quality, lab-grade Pyrex and Kimax flasks can sometimes break from thermal shock.

The round-bottom "Florence" flasks are more suitable for boiling, though their shape isn't exactly conducive to use on kitchen stoves.

Hmmmmm, I was unaware of the "student grade" classification (although I shouldn't be surprised, given the amount of glassware my students broke when I was a TA).

Any way to tell from looking at the flask itself? Any brands you know of that don't sell student grade glassware?

 

[MaxStout]

I think lab glassware is graded based on ASTM standards and tolerances. (Any lab rats here who might be able to confirm/clarify this?) The so-called "student grade" are probably factory culls that have minor imperfections making them unsuitable for more demanding lab applications. Also, the precision of the graduations may be lower (many low-cost beakers and flasks will state something like "approx." or +/- 5%).

I have a 2L Karter flask (from Amazon) that is student-grade. It came with a few little scratches and tiny bubbles in the glass. I don't heat it directly, but have poured boiling wort from a saucepan into it and set the flask in an ice bath to quickly cool it. No problems (yet).

I think you can buy Pyrex and Kimex brand glassware from lab supply companies and get the higher grade stuff. Of course, it will cost more.

 

[kleinstadt]

I think lab glassware is graded based on ASTM standards and tolerances. (Any lab rats here who might be able to confirm/clarify this?) The so-called "student grade" are probably factory culls that have minor imperfections making them unsuitable for more demanding lab applications. Also, the precision of the graduations may be lower (many low-cost beakers and flasks will state something like "approx." or +/- 5%).

I have a 2L Karter flask (from Amazon) that is student-grade. It came with a few little scratches and tiny bubbles in the glass. I don't heat it directly, but have poured boiling wort from a saucepan into it and set the flask in an ice bath to quickly cool it. No problems (yet).

I think you can buy Pyrex and Kimex brand glassware from lab supply companies and get the higher grade stuff. Of course, it will cost more.

Bah. I have one of the same Karter Amazon flasks (3L). It's crashing a starter right now, but I'll examine it for flaws once it's empty and clean.

I think (stress on think) that most borosilicate glass should be able to handle boiling liquid to ice bath pretty well. It's direct heating that I'm really interested in.

I'll look into stuff from lab supply companies, thanks. Good idea.