I've never had that problem, but I always make it 1 part water to 1 part
sugar. I know (and you know, having done it) that you should theoretically be
able to make it the other way, but if you can't figure out what's wrong, you
could always try changing the ratio.
> I’m having a hard time with my latest batch of simple syrup – it’s
> crystallizing practically before my eyes. I’m using an empty dry
> vermouth bottle (small size) and I’ve had a previous batch in the
> bottle before without problem. I made the syrup the way I have
> before – two parts sugar to one part water, heated to barely a
> simmer. I’ve already heated the bottle up by placing it in a small
> pot of water to break up the sugar and then poured it all out into
> another small pot to reheat and stir but it crystallized right back
> within days. The last batch lasted about six months or more at room
> temperature before I finished it all without incident.
>
> I can’t figure out why this batch is different somehow; I’ve got a
> little Mount Vesuvius in there which, I have to admit, looks kind of
> cool but still…..
>
> Any thoughts, advice?