Originally Posted by brewer1222
Unfortunately I didn't do FG and OG, I was worried about contaminating/wasting beer. I'm going to start with the next batch I brew.
I left it in the fermenter for 3.5 weeks - how would the yeast fail to attenuate?
With proper sanitation, taking your SG is not a contamination risk. And it's far from wasting beer. Not taking an SG and overcarbing a batch and having bottle bombs is a waste of beer!
The yeast could fail to attentuate due to temperature or due to underpitching, just to name a few. Taking your FG would tell you if you reached the finish line or if you need to help it along.
Some extracts will leave a lot of unfermentables that can give you a sweeter taste as well.