Graphs of Sight Glass Temps during Boil - Surprising results

**passedpawn** · 02-04-2012, 07:01 PM

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.

**passedpawn** · 02-04-2012, 07:03 PM

Here's the pastuerization chart I use

postal_penguin · 02-05-2012, 12:02 AM

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.

D0ug · 02-05-2012, 12:22 AM

Stand back! passedpawn is doing science in here!

**passedpawn** · 02-05-2012, 12:38 AM

Quote:

Originally Posted by postal_penguin

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.

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.

rollinred · 02-05-2012, 12:50 AM

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

**Bobby_M** · 02-05-2012, 12:53 AM

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.

**JoeyChopps** · 02-05-2012, 12:57 AM

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

**runningweird** · 02-05-2012, 12:58 AM

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

**Bobby_M** · 02-05-2012, 01:04 AM

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