I had a gallon extra wort from an IPA that I tossed some Simcoe and Nottingham I had laying around in and dropped it all in two 1/2 gallon Mason jars. I put the tops on loosely and it looked like a light krauzen built up, but I never could tell if it was actively fermenting (no bubbles in an airlock). I wasn't very critical of this brew so I didn't take an OG. After a week I transferred it into a demijohn and any fermentation is very slow (airlock not bubbling much or at all). It smells just fine with no band aid, sour, etc. scent.
Has anyone ever used Mason/Ball jars to ferment? Should I just let it ride or make sure to take a gravity reading at this point? Let me know your thoughts.