Mash temp

[lcooper72]

Bought a second thermometer to put in hot liquor, and one in mash tun. Added my 168 water trying to get 157 mash temp. When I added the water it went to 170! I think there is a problem with one of the thermometers ( obviously). My question now is, I wanted a high temp, 157, to yield a more sweet wort for an oatmeal stout. I hit an initial high temp, but dropped to low, am I going to turn out dry or sweet? My temps every 15 minutes go like this 170; 140; 152; 148; 150. Thoughts?

 

[duboman]

Bought a second thermometer to put in hot liquor, and one in mash tun. Added my 168 water trying to get 157 mash temp. When I added the water it went to 170! I think there is a problem with one of the thermometers ( obviously). My question now is, I wanted a high temp, 157, to yield a more sweet wort for an oatmeal stout. I hit an initial high temp, but dropped to low, am I going to turn out dry or sweet? My temps every 15 minutes go like this 170; 140; 152; 148; 150. Thoughts?

In all honesty it's hard to say because admittedly you have a thermometer that does not appear to be so great and your temps are all over the place.

It looks like you might have been getting a lot of hot spot/cold spot readings. Are you stirring the mash to get everything mixed up?

Get a new thermometer or be sure to calibrate the one you have!

 

[WoodlandBrew]

Here is how to calibrate your thermometer:
http://woodlandbrew.blogspot.com/2013/01/how-to-measure-thermometer-drift-to.html

And information on what to expect from mash temps.
http://woodlandbrew.blogspot.com/2013/01/measured-mash-temperature-effects.html

A 12°F swing is pretty large. You might want to do something about stabilizing that. Perhaps pre heating the mash tun? Insulating the lid of the cooler-tun?

Looks like your average temperature was about 148, so if your thermometer is accurate that would mean a highly fermentable wort.

 

[Wynne-R]

Ice water is not the same as a proper ice bath. If you put ice in a glass of water it’s about 40F.

A chemist friend wrote this for me:

The water/ice must be pure, as in distilled.
Use slush (crushed ice) with the water level slightly below the ice. When determining melting point remember that water is densest at 4C so the ice/water mixture must be continuously well stirred or the water at the bottom will be 4C and the rest of it somewhere between 0C and 4C (magnetic stirrer works best). A steady well-stirred temperature is 0.0C.

The good people at Thermoworks have a video.
http://www.thermoworks.com/blog/2010/10/making-a-proper-ice-bath/

Boiling point depends on pressure. 212F is for absolute barometric pressure of 29.92" of mercury at sea level. It decreases 1.8F per thousand feet elevation. For example water boils at 211F at standard pressure at 555 feet.

Most thermometer errors for homebrewers are caused by electronic thermometers that got wet. If your calibration shifts by more than a degree, be very wary.

I recommend everybody get a glass analog thermometer to use as a reference. I got mine at the LHBS for eight bucks.

 

[WoodlandBrew]

Thanks Wynne,

I'll make sure to clarify that post so that less people make those mistakes.

I recommend everybody get a glass analog thermometer to use as a reference. I got mine at the LHBS for eight bucks.

What makes a glass thermometer more accurate?

 

[Wynne-R]

Well, it’s not going to get wet for one thing. It’s stable and the linearity should be very good.

It’s not necessarily more accurate, I would say a glass thermometer is more dependable.

Digitals are handy, but they can get wacky. They are convincing liars. Even when they’re working correctly the resolution is better than the accuracy.

Take the Thermapen, for example. It is rated ± .7° F, so when it reads 153.0 ° F what it’s actually saying is somewhere between 152.3° F and 153.7 ° F. So basically it’s within a degree, about what you get with a glass thermometer.

Most digital thermometers aren’t even rated for accuracy. It’s nice to have something to compare it with. When the digitals go bad you can get big errors at mash temps and still be fairly close at freezing.

 

[WoodlandBrew]

I agree. If you want something that is accurate, look for an accuracy specification. Digital thermometers can be deceptive. The two that I have show a 0.1° resolution but only be accurate to +/- 2°.

 

[lcooper72]

All that is helpful. The thermometer I was using came with a turkey frier, not to accurate! I was shooting for a sweeter stout, having the low temp may have turned it into a dry one The comment re the glass thermometers is helpful as my other one is just a good old green line floating thermometer. Think I will get a second one. Why does accuracy have to come from glass devices? I mean beer and fragile glass objects not always the best mix, as evidenced by my trail of broken hydrometers!