Brew Day: Step by Step


STEP 8: Boil

The Boil Kettle should now be full up to the 14.9 gallon mark.

If desired, after a few minutes take a sample and allow it to cool to around 140F and measure the wort pH using the pH meter. It should be around 5.0 to 5.5 (measured at mash temperature). If it is too high you may want to consider adding some 88% lactic acid to get it down into this range. If the mash pH was ok then the wort pH is most likely fine too unless the water you use is very hard. A proper pH helps produce a good protein break during the boil (more on this below) which in turn helps with beer clarity and long term stability. A boil pH that is too high can also cause harsh hop bitterness.

Measure the pre-boil gravity using a hydrometer and test jar to see if we met our target. It should be:

Gravity units (GU) = (Target Original Gravity - 1) * 1000 * Post-Boil volume at 68F = (1.048 - 1) X 1000 X 12 = 576

Pre-boil gravity = ((GU / Pre-Boil volume)  / 1000) + 1 = ((576 / 14.9) / 1000) + 1  = 1.039

Remember that gravity changes with temperature and not all tools (such as floating hydrometers) compensate for temperature. A hydrometer will be calibrated to work at one specific temperature, usually printed directly on the paper scale inside. For example, our target gravity of 1.039 is relative to 60F as that is the temperature at which our hydrometer was calibrated by the manufacturer. It will probably read closer to 1.023 at 140F. BeerTools Pro includes a handy calculator to convert the specific gravity from one temperature to another. After boiling water off for 90 minutes the wort concentration will increase and be closer to our 1.048 target gravity (again, relative to 60F). When using a hydrometer to take a gravity reading, give the hydrometer a spin first to dislodge any air bubbles and always read the lowest part of the water line (the bottom of the meniscus).

If the A-M light on the Boil PID is not on, press the A/M button to enter manual mode. You should see the lower green SV number display as "M XXX" where XXX is a number. If the "M" is not displayed press the SET button to switch the display mode. Press the UP/DOWN buttons on the Boil PID until the lower green number reads "M 100". We will be firing the Boil Kettle element 100% of the time until the wort is at boiling. Remember that the Boil Kettle PID is run in manual mode instead of automatic. For more information see STEP 9: Wire up PID controllers of our control panel build instructions.

Turn the ELEMENT SELECT switch to BOIL. The Boil Kettle element now fires continuously to heat up the wort. It takes approximately 30-45 minutes to heat 14.9 gallons of wort from the sparge temperature of around 140-150F to boiling. It's best to keep the lid off during this period so that you can watch for boil-overs as the temperature increases. If brewing indoors, run your hood fan at high speed to exhaust any excess heat and moisture. 

As the wort heats up, a thick foam appears with a darker crust (which some brewers call 'foop'). Scoop it off and discard using a skimmer if desired. This thick foam is made up of coagulated proteins. Some believe it can cause off-flavours (mostly in lighter beers such as our Blonde Ale).

As boiling approaches a thin foam will rise. This is the 'protein break' or 'hot break'. Watch and stir with the skimmer as required to reduce the amount of foam and avoid a messy boilover. Dipping the skimmer in cold water periodically helps. Eventually the foam will subside and fall back into the wort. Once boiling, press the DOWN button on the Boil PID to reduce the heating element duty cycle but still maintain a good vigorous boil. We find that 75-85% works well but this will depend on the boil volume, ambient conditions, and heating element power.

If using boil salts, add them at this time.

OPTIONAL ALARM: You may set the Boil Kettle alarm to sound once a temperature just below boiling is reached (such as 208F) to warn you that the wort is about to boil and that the possibility of boilover may occur. Press and hold the SET button on the Boil Kettle PID until ALM1 is displayed. Press the UP/DOWN buttons until 208 is displayed. To exit the setup menu, wait 10 seconds. Turn the Boil Kettle ALARM switch ON. When the wort temperature reaches 208F the alarm will sound, warning you of the possible boilover. Turn the Boil Kettle ALARM switch OFF to turn off the alarm. Easily distracted brewers may prefer to also run the Boil Kettle PID in automatic mode set to 208F instead so that the boiling is never actually reached. Once the alarm sounds, switch over to manual mode at 100% and watch carefully, stirring as needed.

We will be boiling the wort for 90 minutes instead of 60 minutes which is typical for most beers. We are boiling 50% longer as Pilsner malt is more apt to produce dimethyl sulfides (DMS) and a longer boil time helps drive off more DMS causing compounds (excess DMS results in a 'cooked corn' taste and aroma in the beer). Some beers where caramelization is wanted (for example, barleywines) can benefit from an even longer 120 to 180 minute boil. For more information on boil times see page 61 of Brewing Better Beer.

The time starts after the foam has subsided. Press the 4/3/2/1 buttons on the Timer until the lower number reads "90:00". Press the RESET button to start the timer. The top number on the Timer will count down from 90:00 to zero.

OPTIONAL ALARM: To be notified when the 90 minute boil is finished, turn the Timer ALARM switch ON. Once the alarm sounds turn the Timer alarm switch OFF or press the RESET button.

Leave the Boil Kettle lid off during the entire boil. The DMS causing sulfur compounds in the wort must be boiled off.

Hops are added during the boil to offset the sweetness of the malt. Our recipe calls for one hop addition at the 60 minute mark, which is 30 minutes into our boil. When the timer reads "60:00", add the hops. These hops will be boiled for a total of 60 minutes. This is our only hop addition for this recipe. Different recipes may call for hop additions at various times. Generally speaking, hops added at the start of the boil add bitterness, hops added in the middle of the boil add flavour, and hops added near the end add aroma. Some recipes will even have you add hops to the mash (called 'mash hopping') or to the Boil Kettle while sparging (called 'first wort hopping') to create complex hop flavours and aromas. For more information see Chapter 5 of How to Brew and Chapter 2 of Brewing Better Beer.

When the timer reads "15:00", add the Whirlfloc tablet (clarifier) to help with wort clarification.

When the timer reads "00:00", turn the ELEMENT SELECT switch to OFF. The boil is complete!

Measuring the wort pH and specific gravity in the Boil Kettle before boiling to see if we hit our targets:

Foam starts to appear a few minutes after turning on the Boil Kettle element:

As we approach boiling, the foam gets thicker and darker (called 'foop') that we scoop and discard using a skimmer.
'Scooping our foop' also helps reduce the chance of boilovers.

Foam continues to build as we near boiling point. Watch and stir as required to avoid boilovers.

Eventually the foam starts to fall back into the wort and we are left with a vigorous boil:

While boiling we usually take the time to empty and clean out the Mash/Lauter Tun. The spent grain is recycled.

We organize our boil additions into containers beforehand. Less chance of forgetting something! 

After the boil is complete, the wort looks like egg drop soup. A good vigorous boil and Whirlfloc helps coagulate proteins:

Coagulated proteins and whole hops at the bottom of the Boil Kettle.
The wort itself should be clear which is the sign of a good vigorous boil and proper use of clarifying agents:


The video below shows boiling in action: