I’m wondering how safe it is to boil the wort in my Erlenmeyer flasks (for a starter). I know the glass has a low coefficient for expansion like Pyrex, but I see a lot of mixed advice online and in person.
Some websites advise against directly heating it at all, and some do. When I asked a brewer/employee at a LHBS he advised me to not use an electric coil stove because it creates cold gaps between the metal coils in the glass, and said heating on a gas stove or electric induction stove would be just fine. Before I heard that, I had actually heated on an electric coil stove and didn’t notice any problems. Since looking into this matter I have heated my flask on a gas stove and haven’t noticed any problem signs, either. (So I’ve only boiled wort directly in the flask twice).
I figured I’d ask the brightest minds in the brewing community for guidance, so thanks for your time everyone.
I’ve boiled a 2L on a gas stove (quick boil-over too).
I think I’d be hesitant on an electric, for the reason you outlined. My mother used to place a wire ring on the element and put her pyrex on top of that. She never had a problem, but that’s all the guarantee I can give you.
In the lab we use hotplate/stirrers regularly. They have ceramic tops.
Same here. I only stopped because I find it easier to stir up the clumps and prevent boilovers in a pot and then pour through a sanitized funnel into the erlenmeyer flask than boiling in the flask itself, even with Fermcap-S.
A friend had one crack after multiple uses on an electric stove. After that, continued to use the electric stove, but did not use full power any more. No more problems yet.
Still, be prepared to deal with boiling liquid in cracked/broken glass if you choose to boil in it. No kids/pets in the area. Have a means of grabbing the hot flask and moving it to a safe location (a large pot, sink, etc.). And probably want to wear some decent footwear.
I have been using mine on a gas stove with no issues for many years and once boiled goes right into a cold water bath to chill-no issues but I have friends that used electric coils and it cracked:(
I have a ceramic cooktop with no issues…other than a bad boil over (twice) :o If you are really concerned with using your electric stove maybe do a double boiler. Fill a bigger pot with water and put the flask inside of it? Obviously will take a little longer but it will work nicely.
To add to the great advice so far, as a former lab chemist, I’d use a Pyrex flask on a gas stove or ceramic top electric, but certainly not on a coil, for the hot spot reasons mentioned. It won’t work on an induction top, because that requires cookware with ferromagnetic properties.
All that said though, every time I’ve tried to use the erlenmeyer directly, I’ve had awful boil overs! :o
I’ve been making starters directly in Erlenmeyer flasks for a couple years now. Some on an electric coil stove, but never directly on the coils. Use some sort of diffuser between the coils and the flask to avoid the hot spots. Mine was a doubled up, perforated aluminum thing sold as a “double boiler”. Takes forever to get to a boil, but at least you get good control of the heat to limit boil overs. I’ve switched to a small Coleman propane camp stove that screws directly onto the bottle and have had pretty good success provided the flask is adequately sized. I had a 500 ml crack using this small burner but 1L and 2L flasks have been good to go with the heat output available.
As for the boil overs - It is best to keep your initial volume of wort to about half the total flask volume Then 5-6 drops of a foam control agent per 1L of wort usually keeps the foam inside the flask, even with Wheat DME. Don’t forget the stir bar before you start the boil if you’ve got a stir plate. As someone else here mentioned, Cold bar+hot glass=unhappy brewer.
Also consider using a “lab thermometer” (cheap glass type) pushed through a foam stopper and into the wort during the boil and ice bath. It’s one slick, sanitary way to make sure you hit your pitching temp.
Is it necessary to prepare starters with a full boil? Avoiding the flask boil-over is hard to manage, and realizing I never thought to use a smaller burner. Seems like sanitation-wise being above 180 is necessary, and thus holding in the 195-200+ degree range should be more that sufficient.
The steam from boiling will sanitize the walls and whatever foam/foil cap is on the flask, which is convenient but can be accomplished other ways too. I’ve been bringing it to boil and then removing from heat and allowing it to cool slowly. I’m sure it stays above 180 for quite a while this way. Steam sanitizes very quickly, so a few seconds should do it.
There is a difference between sanitation and sterilization. If you want sterilized wort, I’m not sure 180 would do it. But if you’ll only use the yeast in a single batch, sterilized wort isn’t needed.