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My dad found an old Kimax (26500) 1000mL Erlenmeyer flask that has been in his attic for the last 30 or so years and gave it to me. I'd like to start using this to make starters, in conjunction with a stir plate. I am concerned about the ability of the glass to handle the heat from my electric (glass top) range, and then the cold of an ice water bath. I'm pretty certain that these are used in a lab, but in my chemistry classes, we used gas for heating, rather than electric.

Mostly, I'd just like a little more confidence that the flask won't shatter while I'm in the midst of heating a starter. Will it handle the direct heat from the electric stove top?

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6 Answers

up vote 3 down vote accepted

Despite Kimax being a lab grade glass, you don't have lab grade heating equipment. The problem I have found is that most electric stove users have the exposed metal coil that the pot or flask sits right on. That contact doesn't happen in the lab environment. In the lab we have heat plates that have a ceramic type cover between the glass flask and the heating element itself. This evenly distributes the heat where your coils on the electric stove doesn't.

If you have an electric stove that has coils embedded under a glass cook top, you are good to go. I have been using some flasks this way for years not worries. I do let it cool a little bit off the burner before dumping it ice cold water. Even the best labware tends to weaken with such an extreme swing in temp.

Its not part of your question, but 1L is sort of a small size to be boiling extract in. Give it a try and watch it like a hawk. The smaller opening is like putting a lid on boiling pasta or potatoes eventually it bubbles right over. (That's what Denny was concerned with in his answer). You might be able to get away with some foam control. I haven't tried it but a few buddies do and they seem to get by with it.

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Not only is 1L small to boil in, it's too small to make a starter in. With that small a volume, it's possible you might stress your yeast because there won't be enough food left for them to rebuild their glycol reserves. –  Denny Conn Jul 5 '11 at 21:22
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I agree that 1L isn't really big enough for a quality starter if you want to improve cell #. 2L is really where to start, even that is a little small. 4L flasks for a 2L starter volume is the way to go for most applications. –  brewchez Jul 6 '11 at 19:19
    
4 L e-flasks have to be expensive in Kimax or Pyrex. –  drj Jul 8 '11 at 22:23
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Google research indicates the flask should be up to the heat, and more importantly the rapid change from boiling to ice bath.

Additionally, discussion from homebrewers appears to back this up with experience, though several people indicate boil-overs are more of a problem.

I for one would avoid subjecting any glass to such extremes, as a pot works perfectly well for the boiling and cooling, at which point you can transfer to the flask, but I'm also recovering from a serious carboy shattering accident (dropped, not heat related), so my feelings about glass are biased.

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Many people do it. After trying it a couple times, though, I stopped doing it. The potential for a boilover is so great that it's not worth it to me. In addition, I've heard too many stories of flasks cracking while on the stove, even though they supposedly shouldn't. There are enough downsides that although it can theoretically be done, you should consider whether you're ready to accept the potential problems.

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Check for scratches in the flask before doing the hot then cold immersion thing. Kimax as well as Pyrex will deeply crack or burst suddenly when there are scratches and hairline cracks in these conditions.

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I've had success boiling in an Erlenmeyer flask (on a glass top electric stove) then immediately cooling it in the sink with ice water. But boilover is enough of an annoyance that I feel like sanitizing the flask separately and just boiling in a pot is less hassle overall.

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I would sit the full flask in a pot of water and bring it to a boil. Then start cooling it in the pot by placing the pot in cold water. Once the flask cools a bit, remove it and place it in the cold water. This will prevent thermal shock, boil overs would not make a mess and no fear of contamination from transfer.

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I was just going to add the same answer - use a water bath - it's gentler on the flask - especially the relatively cheap ones that most LBHSs seems to stock which are quite thin-walled. Just a couple of weeks ago, I had a 5l conical crack - boiled on the glass-top and left to cool - when I tried lifting it, a round piece came away from the bottom. –  mdma Nov 6 '13 at 9:57
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