Bad thermometer calibration, what should I expect?

I discovered this morning that my brewing thermometer has been calibrated 4 degrees low, so basically I've been heating my water, mashing, sparging, cooling, basically doing everything but fermenting at 4 degrees higher than I thought I was.

What problems should I look for in the beers I have brewed this way and what improvements should I expect in future batches now that I have corrected it? the only one I know of would be to expect high FGs, but other than 1 extract batch I made before I started AG, I haven't seen that.

 

I once had a fermentation get stuck because I mashed too high. Too many unfermentable sugars preventing the yeast from doing what they need to do. If your beer is fermenting fine, you should just expect a higher FG.

 

It seems like the last couple of recipes that I've made have had higher target mash temperatures, one of them being as high as 158. My point here is that there seems to be a wider range of temps that will yield a good brew than I had originally thought, so I think you'll be fine. In my opinion, the attenuation that you get is much more strongly influenced by the yeast you choose than by your mash temp. Your final result might be a point or two higher in gravity than you had intended, but I think you'll be fine.

 

Mash temps would be the biggest concern. 4 degrees can be the difference between a nice dry crisp beer that fully attenuated and one that turns out maltier and sweeter than intended with lower attenuation.

It's good you found this out and can now know that your process is what you expect it to be

 

That's why you should have several thermometers. I always have a couple standard thermometers and a digital that I use the most. I always check calibration before every brew and before I mash, I check with both thermometers.

 

But that is assuming they are both correct when in fact they could both be off....

They should read 212 for boiling and 32 for ice water. If either reading is off then it is possible your mash temps will be off as well

 

True which is why I always calibrate the digital. The other 2 are spot on.

 

This has been one of my gripes (as a noob)is finding an "accurate" thermometer. remember the 212 and 32 are sea level temps

 

Did you use a proper icebath? You need more ice than water and you have to stir it.

http://www.thermoworks.com/blog/2010/10/making-a-proper-ice-bath/

Atmospheric pressure doesn’t affect the freezing point.