WHY did my Bomex flask crack!?

When making starters i have always boiled the wort in a pot and then moved it to my 2000ml bomex erlenmeyer flask for pitching. every time i've ever read anything anyone has written about starters and flasks they always said how convenient it is to just put the flask right on the burner, so i said why not, one less pot to wash. right after it started to boil i heard a loud pop and there was a circular crack all the way around the bottom! WTF?! is it because i have an electric stove? isn't bomex just another brandname like pyrex and they're all heat safe? i've heated plenty of flasks during chem classes to much hotter than what an electric range can put out and i've never had this happen. maybe just bad glass? someone please tell me i'm not crazy!

Normally, when you use Pyrex on an electric stove, you have a piece of wire in the shape of a star that sit between the flask & the heating element.

I use my flasks with a gas stove and have no problem going from boiling to an ice bath with my starters.

SenorWanderer said:

... i've heated plenty of flasks during chem classes to much hotter than what an electric range can put out and i've never had this happen. maybe just bad glass? someone please tell me i'm not crazy!

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Well, i've done a bunch of chem classes, but we never heated with electric ranges. Gas heat is much more "gentle" and less localized than an elictric element. Thus , the star shaped spacer Ed mentioned. Sorry about your flask. Bummer.........

I dunno about bomex....pyrex is a trusted name around these parts. Usually, though, you don't heat with an electric element directly. In chemistry practice, you'll use a "sand bath" where the sand acts as a medium between the element and the glass. That, or use gas.

i've heard that you put it in a saucepan with a little bit of water in it and heat up the flask in there so it's not directly on the heat.

does this sound right? cuz i've wanted to try it

I've used my Pyrex flask directly on an electric burner without issue, but I don't turn the heat up very high. From a glass website: Pyrex glass is good for normal use temperature of 446 degrees F and maximum use temperature 914 degrees F.

Mine cracked on my electric stove the second time I used it. Pisses me off because there's nowhere locally to buy one and I'll have to order through B3 to get another one and pay s/h. I tried putting the flask in a big arse pot and boiling it that way, but after 30 minutes of the pot at a rolling boil, the starter wort never boiled. And the flask made a helluva racket bouncing around in the pot. That's when I decided to just put the flask on the burner. Going to try heating it on my little gas coleman stove once I get a new flask, and see if that works better.

why not sanitize the inside of the flask first, then add the boiling wort to it?

mrkristofo said:

why not sanitize the inside of the flask first, then add the boiling wort to it?

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I boil my starter in the flask with foil on the top. Everything is sanitized in the process. When done, off to the ice water bath for a quick chill. Works great every time, but I do use gas for boiling it.

I have used gas to boil a starter in a 1L flask, then placed the flask in a sink of ice water only to have it crack on me. These flasks are good but do have their limitations.

And if using electric try to find a way to diffuse the heat as others have said. I use these burner plates even on a gas range.

Now, I haven't bought a flask because I've historically been a dry-yeast guy and therefore rarely have to make starters - but since I'm using more liquid yeasts these days, do you think I would have the same problems with my ceramic cooktop? Or are these issues just limited to the old-school type of electric burners?

the_bird said:

Now, I haven't bought a flask because I've historically been a dry-yeast guy and therefore rarely have to make starters - but since I'm using more liquid yeasts these days, do you think I would have the same problems with my ceramic cooktop? Or are these issues just limited to the old-school type of electric burners?

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You'll be fine with a ceramic cooktop. They work great with pyrex cookware.

I put my first starter in a pot with some water last night.. the water boiled but the starter did not. So i took the flask out and put it directly on the ceramic burner. I kept it on medium heat and it boiled perfectly

This is an interesting topic because I have used laboratory stir/hot combo plates and they don't seem to be much different than a normal electric burner. OTOH, I was using 150mL beakers and not 2L Erlenmeyer flasks.

I'm always paranoid about glassware, though, even borosilicate lab grade stuff......slow heating over a flame and slow cooling.