Graphs of Sight Glass Temps during Boil - Surprising results

This came up in another thread, so last night while grilling I got my electric HLT going.

The question was this: during a boil, how hot does the liquid in the sight glass get. The hope was that it got high enough to kill the beer-ruining bacterial and wild yeast.

The result was that it never got there, and I'm surprised. Here's the data. 10 gallons, with pump running full bore to ensure good circulation. Bobby_M sight glass. One thermocouple is down in the middle of the boil, the other is slid into the sight glass, at about the 8g mark. The temp in the sight glass never got above about 130F.

BTW, my logging thermometer apparently somehow dropped about 20m of data from the 0:29 to 0:51. Or maybe I did that, der. That is why both graphs appear to be a straight line during that period.

Here's the pastuerization chart I use

It doesn't really matter what the beer in the sight glass gets to, there is enough turn over of the liquid in the sight glass that the beer should at some point be at full boil.

Watching my sight glass you can see it go up and down by about 1/4 gallon suggesting that beer is being sucked in and out of the sight glass. Also on my gas burner you can actually see some boiling in the sight glass if you crank it high enough.

Stand back! passedpawn is doing science in here!

postal_penguin said:

It doesn't really matter what the beer in the sight glass gets to, there is enough turn over of the liquid in the sight glass that the beer should at some point be at full boil.

Watching my sight glass you can see it go up and down by about 1/4 gallon suggesting that beer is being sucked in and out of the sight glass. Also on my gas burner you can actually see some boiling in the sight glass if you crank it high enough.

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Do you have an electric Kettle? My kettle heats from about 6 inches above the bottom, well above where the sight glass is connected. I don't think I get much turnover. I'll do another test with some food coloring to test that, though.

Let us know how the food coloring test goes. I am willing to bet it completely dissipates through a 1 hour boil.

I'm glad you put the effort into this and I am surprised to see it sit at 130F, but it's not that hard to understand in an electric fired BK. Of course I do have concerns that there may be an unreasonable panic by folks that have sight glasses installed so I want to make sure everyone realizes the details.

The sightglass wort would be much hotter in a flame fired BK (as mentioned by a few, some are boiling the wort in the tube).

If you chill through an external chiller, there are absolutely no concerns here whether you heat with flame or run electric. That small volume will drain into a bath of 210F wort before it is chilled. Based on the chart, it's instantly pasteurized.

Where it starts getting questionable, though I am still not convinced there is reason for concern, is when you fire electric only AND chill with an IC. The only way it would be an issue is if that small volume of wort does not turnover with the main wort. Even if the element is above the sight port, the boiling action creates a lot of current in the kettle.

The good thing is that grabbing your hop bag and bobbing it up and down in the boil anytime in the last 15 minutes would turn that wort over. The other idea was to just keep a short length of 1/2" ID tubing nearby, hold it to the tube and blow into it once. If it was 130F before that, the stuff that rushes back in after that should be up near 190F. That would be a great thing to test next batch (both methods).

Thanks again for your efforts.

I guess I'm just nurotic I used blow the wort in the sight gauge when bubbles get in it to get a true reading on volume so mine always gets back in the pot neat study though

does the diameter of the sight glass have any impact on re-circulation during the boil?

I don't know but all tubes I've seen used are 1/4" id.

passedpawn said:

Do you have an electric Kettle? My kettle heats from about 6 inches above the bottom, well above where the sight glass is connected. I don't think I get much turnover. I'll do another test with some food coloring to test that, though.

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No I have a Blichmann Boilermaker and Top tier. I don't usually have the flame high enough to boil in the sight glass but I do notice that hot break and hop particles appear in the tube so there must be turnover.

And if you do the food coloring test may I suggest adding the food coloring only to the sight glass and seeing if it dissipates.

I brewed this weekend. Unlike the initial test, which was with clear water, this time I could see the coagulated protiens and hop material floating around in the sight glass.

There is some pretty good flow going on in there, with hot stuff rising and cool wort going back down. Based on this, I guess there shouldn't be much concern.

I did give it a blow during the boil to make damned sure though.

Ultimately, as pointed our previously, won't the 'cool' wort in the sight glass mix with the boiling/near-boiling wort as the wort drains from the keggle, thus sanitizing the cooler sight glass liquid? This assumes you are using a CFC or plate chiller, of course.

Neat experiment. :rockin:

mccabedoug said:

Ultimately, as pointed our previously, won't the 'cool' wort in the sight glass mix with the boiling/near-boiling wort as the wort drains from the keggle, thus sanitizing the cooler sight glass liquid? This assumes you are using a CFC or plate chiller, of course.

Neat experiment. :rockin:

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Not If you recirculate back to the kettle (after the plate chiller). That, in fact, is what I do.

But the convection currents in the tube get everything mixed up pretty well. I might still do the dye test just to see, but I'm 99% comfortable after this weekends session.

I normally see a fair amount of action within my sight glass, perhaps the thermocouple and wire disrupted the normal flow?

If you are worried about the sight glass wort not being pasturised then don't use it. At the end of the boil put a stopper on top and drain the kettle retaining that portion

Thanks for diving into this for research's sake. I personally direct fire and actually have problems with my sight glass bubbling over, but I can see where the potential concern can come from e-kettle users. With that being said I dont think I would be concerned and we all should keep patronizing BobbyM

Interesting work, passedpawn. If there's a biofilm in the sight glass I don't think it matter much whether there is recirculation between there and the main kettle, as the bugs aren't free floating. But my gut feeling is conditions won't favor growth in the sight glass.

So, to ensure there is no bacterial contamination from the sight glass, you are blowing into it? Using your MOUTH, which tends to be a natural bacterial warfare lab?

Cpt_Kirks said:

So, to ensure there is no bacterial contamination from the sight glass, you are blowing into it? Using your MOUTH, which tends to be a natural bacterial warfare lab?

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Yes. I justified it at the moment: feasibility test. I'm building a toolbox aerator that will replace my mouth.

I've been slowly putting the aerator together that will connect to the top of the sight glass with a quick-disconnect pnuematic connector. I will use it for stirring my HLT water, and also for aerating my wort in the boil kettle while chilling.