I think i effed up my last batch. I brewed a Lagunitas IPA form CYBI. I used a new thermometer and my strike water was way too hot. I was shooting for a mash temp of 160F. I overshot and hit 178F!! For fear of denaturing all of my enzymes I promptly got it cooled down to 160F. Next my manifold in my MLT came off. I had to empty the tun and fix it. Somehow I still hit my preboil gravity. It's been fermenting at 68F for 4 days with WLP002 yeast and my refractometer (and hyrdometer) is telling me I'm at 1.005. What the hell!!? I was shooting for a terminal gravity of 1.018. This is now my second beer to finish way too low. My last Pale Ale finished at 1.004. I was shooting for 1.010. Any ideas why I'm going so low? I don't think it's wild yeast. I'm pretty crazy about sanitation.

Cheers!

What type of thermometer do you use? Did you properly calibrate it before using it? I can almost guarantee that your thermometer is the culprit. Try comparing yours to a brew buddy's that has consistent and proper finishing gravities and see how far yours is different from his. You could always try to brew a standard recipe (like from BCS, or CYBI) again and see how far off your final gravity was and make adjustments from there. Sounds like yours is reading higher than what it really is.

Are you calculating back based on your refract reading? They don't give an accurate straight read on fermented beer. Have you checked your hydrometer calibration (reads 1.000 in water)?

what spider said