Homemade soda-funny taste help?

I've recently begun experimenting with making homemade soda, and after three or four batches, i've run across a problem for the second time(two batches of peppermint made with tea turned out carbonated but under flavored), but my cola took an a fiberglass taste after a few days, and i thought it may have been the... show more I've recently begun experimenting with making homemade soda, and after three or four batches, i've run across a problem for the second time(two batches of peppermint made with tea turned out carbonated but under flavored), but my cola took an a fiberglass taste after a few days, and i thought it may have been the under-prepared syrup and food coloring. However, I made a batch of vanilla-almond-cardamom(tastes like a toasted marshmallow) with a sufficient syrup boil down time, and used no food coloring, but two days into the process it is beginning to smell like fiberglass. Will this pass, or is it because I'm using active dry (bread) yeast instead of brewer's yeast?
Update: Making my own syrup and adding it to club soda completely defeats the purpose of what i'm trying to do-i.e. make an original gift for friends/family, maybe sell small batches in my hometown. Boiling it down makes it into a syrup-which is then used to make the soda-every time you drink soda out of a fountain... show more Making my own syrup and adding it to club soda completely defeats the purpose of what i'm trying to do-i.e. make an original gift for friends/family, maybe sell small batches in my hometown.
Boiling it down makes it into a syrup-which is then used to make the soda-every time you drink soda out of a fountain it's carbonated water mixed with syrup which was probably boiled or superheated at some point.
I never attempted mint-soda-they were two seperate batches.
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