Boil Kettle


STEP 2: Add a temperature probe

The next step is to add a temperature probe to the Boil Kettle. It controls the heating element used to boil the wort. The temperature of the wort is displayed on our control panel as we ramp up from mash temperature to boiling.

We use a short 2" probe. There's no reason to use a longer probe as the liquid is always in contact. The shorter the probe, the easier the Boil Kettle will be to clean.

2" Metric (straight) temperature probe (shown without protective sheathing or XLR connector):

The probe has a metric (straight) thread so that it can be fastened to the kettle wall using the included silicone washer and stainless steel nut. An NPT threaded (tapered) probe such as those used in the Hot Liquor Tank and Mash/Lauter Tun cannot be used here as you cannot fasten them with a nut due to the tapered nature of NPT fittings.

In process control systems such as ours that involve fluid recirculating, temperature monitoring is usually done in the plumbing instead of in the kettle as it helps avoid temperature misreads due to stratification (layering). This is not an issue in the Boil Kettle as the violent boiling action continuously stirs the wort to ensure an even temperature throughout the kettle.

While a temperature probe for the Boil Kettle is not necessarily needed (water boils at 212F so there's really no need to monitor or control it), we do find that displaying and controlling the temperature in the boil kettle has benefits: It helps us minimize the chance of 'boil-overs'. When wort first starts to boil it foams up considerably. If left unattended (brewers are easily distracted), it will result in messy boil-overs. To avoid this we typically run the boil kettle heating element in what's called 'automatic' mode and set the temperature to just below boiling. We also set an alarm to sound once that temperature is reached. The wort is then automatically heated to just below the boiling point without actually going any higher, and an alarm sounds. At that time, we switch over to 'manual' mode and continue heating while watching and stirring to avoid the initial boil-overs.

Being able to control the temperature of the boil kettle is also useful when doing advanced hopping procedures such as a hop stand where you add hops after the boil is complete at varying times and then hold for 60-90 minutes at specific temperatures. Our control panel with advanced temperature control in the boil kettle allows this (unlike a dial-type boil control). This process is used by new popular beers like The Alchemist's Heady Topper. Our Electric Hop Candy (New England Style IPA) explains this process further.

The temperature probe we use comes with a cable that disconnects from the probe, making cleaning of the kettle much easier. The probe as shipped does not come with black shrink wrap or blue flexible sleeving. In previous instructions we showed you how to add these as well as a stainless wire rope to help protect the cable from accidental breaks.

We use an RTD (resistive thermal device) Pt100 temperature probe. Thermocouple based temperature probes are also readily available and are often used in brewing setups. While either will work, an RTD will typically be more accurate and remain more accurate (offer better linearity) over the brewing temperature range we use. RTDs also remain more accurate over time (less drift which means less re-calibration). The cost difference between the two is negligible in our setup.

The exact position of the temperature probe in the Boil Kettle is not critical. We recommend placing it no higher than the heating element to ensure that the probe will always be submersed.

Punch a hole in the kettle using the GreenLee 9/16" round chassis to create a 9/16" diameter hole for the M14x1.5 probe. Refer to Step 4: Punch a hole in the kettle from the Heating Elements section for instructions on how to properly create clean holes using a punch like this.

Do not use step bits or drills bits exclusively as they do not create nice clean holes. 

 Breakdown of the Brew Kettle temperature probe connections:

(A) Silicone washer included with M14x1.5 probe
(B) Stainless steel hex nut included with probe (M14 size, 1.5mm pitch)
(C) Stainless steel liquid tight RTD sensor, 2” probe, M14x1.5 Metric thread
(D) GreenLee 9/16" round chassis or radio (not conduit) punch for making 9/16" diameter holes

(Note: The size of the silicone washer included with the probe has changed since these photos were originally taken)

The temperature probe wires attached:


To install, tighten the M14x1.5 hex nut on the inside of the kettle using a wrench while using a second wrench to hold the temperature probe steady on the outside of the kettle. Tighten until the silicone sealing washer is slightly compressed. Do not overtighten.