Pyrex is shatter-resistant not shatter-proof. Pyrex labware is meant to be used over a gas flame, nothing else. Pyrex, Kimax or other borosilicate glass has a higher chance of shattering if used on electric and ceramic ranges. Because Of this I boil in a pot on my electric range then transfer to a sanitized flask.
Me too, though I don’t think the two-day process is needed. You could boil some water in a flask and wort in a pot. When done, pour the hot wort into the flask and let it cool. Since it’s still hot the chance of contamination is zero and the starter will be ready to innoculate sooner.
That works too. Although I tend to do most things at night anyway, so it would still be the next night before I pitched anything. This was I can boil the concentrated wort, add the chilled water, and away I go. If only sterile filtered water was cheap 
This is what I do. I put the stir bar in the flask and add boiling water to sterilize it all. Then I add the starter wort to the flask and pitch some yeast when it’s cool enough.
Boiling in the flask scares me, though I do recall reading that the majority of problems are with electric elements in that you have an uneven distribution of heat from the element (ie. super hot where the element touches the glass). I suppose you could use a diffuser to eliminate that problem.
cool - I was always afraid the direct heat was going to melt the coating on my stir bar. if you guys say its okay, I’ll try it next time.
Hasn’t yet…
Good to know about the stir bar. I always added it right after I took the starter off the boil. Got my finger steamed a couple of times doing this and if I do not add Fermcap, I can get a volcano.
I’ve been looking around the internet more on this and it seems that if you have a glass or ceramic electric stove it is not an issue. It becomes a problem when you put the flask directly on the electric heating coils. My glass top electric seems to distribute the heat quite well and as I have said, no problems thus far.
However, I don’t want boiling wort all over the kitchen as my wife will kill me. Thoughts on glass/ceramic stove tops versus directly on the element?
Dave
Just to be clear, I haven’t boiled the stir bar on the stove where it might be getting heated directly from the flame.
I boil water and pour it into the flask which has the stir bar in it.
Stir bars are usually teflon coated. According to wikipedia, teflon has a melting point of 621F. It will be fine in the liquid.