Maintaining Temperature

[ajmuzza]

Just having a practice run with my new urn for my first crack at BIAB.

I've lagged my urn with insulation similar to silver backed stuff from Clarke Rubber. After hitting strike temp, i cover the urn which is inside the house with a woolen doona and a sleeping bag. I'm loosing 3 degrees in the first 25mins (measured by digital thermometer with a probe in the urn)!!! As its a practice run I haven't added grain - would this have any insulating effect? Any ideas?

 

[pk.sax]

Solids have greater thermal mass (denser things). This will make it a slower loser of heat.

In essence, yes, grain will tend to insulate itself by being a poorer conductor of heat than water alone.

^ I realised that is not 100% extensible to any application but hopefully answers your question.

 

[ajmuzza]

Thanks. Yep - far better explained than i could have.

As an aside, if you do heat (concealed element urn) during the sacc rest, does it have any adverse effect ie why not just leave the urn thermostat set at 66 degrees?

 

[philmud]

Yeah, that seems like a huge temperature loss rate, especially with the insulation - I get way less in an aluminum stockpot with a thin Fiona for insulation. As PF said, try it with grain - if the temp drops, switch the urn on and bring it back up. Lots of urn users put a cake rack or similar in the urn to avoid burning the bottom of the bag. I use gas, so I stir whenever the burner is on.

 

[Feldon]

Couple of thoughts:

Are you measuring the temp by mixing up the water? Once the element is off the water tends to stratify in thermal layers. Depending where your probe is you might get different readings.

Are you preheating with the lid on? Or putting cold lid on then insulating.

How much air space?. You need to fill to similar volume as will be used in a real brew. To determine if the air space is an issue, cut out a circle of Alfoil and float on top, insulate urn and see if you get the same 3 degree temp drop.

Edit: sp.

 

[earle]

I think once you do a run with grain you won't need to worry. I have a crown concealed element urn which I lag with the same silver backed insulation from Clark rubber, I also have a disk of the insulation to sit on the lid, cut a hole out for the knob. After I mash in I put an old sleeping bag over the lot and only loose about a degree over a 75 min mash. I switch the urn off until mash out.

Another thing to think about if you're going to leave the urn on during the mash is that the thermostat is right next to the element. The grain has quite an insulation effect sitting on top of the element cover so unless you're mixing the grain the heat from the element will not penetrate far into the grain bed before the thermostat turns off the element anyway. I suspect that the centre of the grain bed above the element won't loose any temperature so the urn won't cut in anyway. Just some thoughts anyway

 

[benno1973]

<snip> I get way less in an aluminum stockpot with a thin Fiona for insulation </snip>

Your wife's name is Fiona?

 

[ajmuzza]

Ah yes. Year 10 science is all coing back to me now (if only I hadn't spent all that time trying to make bongs out of conical flasks). Forgot to say I was boiling 12l as a test for a mini batch hence the head space was greater than you'd get for a larger water volume. Problem solved. I'll put pie tray on top and we should be apples.

Thanks guys.

 

[philmud]

Your wife's name is Fiona?

Ha! ******* autocorrect. Fiona = Doona.

Siri - I will pretty much never type "Fiona". Take note.