Rolling boil, temp gauge only reading 97.5deg?

[Ducatiboy stu]

I believe they use a vacuum boil system to make extract.

to draw off the moister

 

[gava]

What I get from this is, not the fact that the boiling is an issue but maybe the mash temp could be off since it's boiling at 97c? so instead of mashing at a 66c he could be mashing at 63 or something? (Im assuming this is BIAB)
I'm thinking that would be more of an issue than the boil, because as people say.. its boiling.. your doing it right.

I'd remove and calibrate within the thermowel don't calibrate without it.. also give it time for the heat to transfer through the thermowel.. Don't just put it in and believe the reading straight off let it settle.

my 2cents..

 

[Camo6]

What's the issue exactly? If it's boiling, then job done. The temperature being read by a device matters naught if you're boiling wort.

Unless you're running alarms for nearing the boil like Qldkev's controller though this could easily be adjusted.

Agree with the advice to calibrate your probes but out of interest would there be much temp variation in a boiling vessel? I imagine the hottest part is at the bottom for gas fired or at the element on electric but would the turbulence of a boil disperse temps uniformly? Would probe placement really matter? Any thermodynamic experts in the house?

 

[TheWiggman]

Not an expert but your description is largely correct. It won't be 100% uniform but for all intents and purposes may as well be. I don't think probe placement would matter.

To get water from liquid to gaseous state it uses a substantial amount more energy than just heating it between freezing to boiling point, which is why it's hard to get it to a boil but once achieved is fairly easy to maintain.
Enthalpy of vaporisation (or latent heat) is the concept, but I'm not too strong on the theoretical stuff. Adr_0 might be able to shed some nerdier light on it, he's less mortal than I.

I've never actually thought about how much difference there might be in boiling temp between wort and water. Maybe there's a degree or two in it? I've never measured it because, well, why? I'm too busy smelling the aroma :icon_drool2: and fending children from the pot.

 

[klangers]

I'd say it's the dissolved salts in the water affecting the boiling temperature.

Thermodynamics/heat/mass transfer is a field that I do a bit of work in. All kettles have some thermal differential in them, other wise all the wort/water would simultaneously boil at all points - which is not what we observe. Instead there are substantial convection currents set up from the density (~= thermal) differentials as well as the evaporated steam as well. A rolling boil shouldn't have such a large difference though, so I suspect it's various dissolved solids.

 

[Dunkelbrau]

What level of TDS would be required to shift the boiling temp that far thoigh?

Unless its a very minerally water profile the first thing I would check is the boiling point of stock standard tap water and calibrate my gear.

Edit: a quick google finds 100g of salt (sodium chloride) in 1kg (L) of water will change the boiling point by 1 degree C.

I'm not sure about the effect of other minerals/impurities, but I would say that's WAY too much to consider it/as the cause. (Happy to be shown data that states otherwise though)

Again, I'd just check calibration first by boiling water on the stove and inserting the thermometer, there should be a screw to calibrate on the back if the dial.

 

[Fat Bastard]

Or might it be that the thermowell is towards the outside of the urn?

Thanks!

I think that this might be at least part of your problem. My kettle has a short probe below the level of the element and it'll read anywhere between 100.3 while the scum is still present ( a very fierce boil) and 98 ish ( a gently rolling boil) it normally hovers around 99.7. By all means calibrate the probe, but bear in mind that the position of the probe and the effect of convection can give a wide range of readings. If it looks like a boil, it probably is!

 

[Mozz]

Basically if you calibrate anything make sure it is against a reliable standard - in this case clean water- not a wort. Where you live (at sea level) it will boil at 100C. If you lived say in the New England highlands or tablelands of North Qld you'd have to adjust the calibration a degree or 2 for difference in boiling temp. If you didn't all your readings would be potentially a degree or two out. It's just basic physics and nothing to do with beer making which I know stuff all about but trying to get my head around.

 

[Flash_DG]

You wont get any gravity points in a vacuum so the whole process is pointless.....and possibly weightless.......so a 1053 brew would be 1000, no more no less.

Why not? a vacuum doesn't eliminate gravity (unless you are in space).

 

[klangers]

I think we can summarise:

1. Your wort is boiling so there's no point stressing about the exact temperature. You can't make the boil hotter anyway without increased pressure or additives (eg glycol), both of which are not really viable.
2. Boiling temperatures will vary depending on altitude, TDS and the atmospheric pressure on that day. Don't calibrate to your boiling temperature because you'll throw off the accuracy of all the other measurements at lower temperatures (eg mashing). Water doesn't always boil at 100
3. It's entirely possible for probe placement to affect the measured temperature due to thermal differentials within the kettle as well as radiant heat losses through the thermowell body into the surrounding air. These heat losses become more pronounced at higher temperatures
4. Therefore, don't calibrate off the boil as it's an inaccurate benchmark and don't stress

 

[TheWiggman]

That's right Flash, because specific gravity is a ratio of densities (density of liquid/density of water). Applying a vacuum to it has nothing to do with density ratios. The specific gravity will remain the same regardless of gravitational pull. You won't however be able to take a measurement of it in zero gravity using a hydrometer, but this has nothing to do with vacuum.

Vacuum evaporation is a different concept altogether and like Nev said, can be used to separate water more easily by allowing the liquid to boil at a lower temp (same reason as for the atmospheric pressure listed above). I'm not sure what the brewing industry uses.

 

[klangers]

When I had a peek at the Coopers brewery, I noticed their extract line makes use of vacuum to concentrate the wort into syrup. This minimises the temperature damage (thermal degradation) on the flavours/bitterness/colour etc.

Dry malt extract can be spray evaporated ("flashed") whereby it is pumped under high pressure through a nozzle into a vessel. The vessel may be under vacuum, but either way the spray atomises the wort and the water flashes off to steam almost instantly.