On Sunday, January 27, 2019, I conducted a boil-off test on my small kettle. It is a 62-quart SS Bayou Classic that I have used for five-gallon batches for years. I have been experimenting with lid-on boiling with my 1/2 BBL system with the BrunDog condenser unit and wanted to trying boiling with the lid on on the small rig to save boil-off while using less electricity with a lower PWR setting. The lid has some holes in it from prior experiments. I think there will be adequate vaporing through those holes for the wort to get rid of the unwanted stuff. Of course, I will have to actually try it to make sure.
11:00 AM: I started with about 7.5 gallons of water in the kettle at 65°F. I put the lid on and applied 100% PWR.
11:35 AM: A full hard rolling boil (likely started a little sooner that 11:35.) Cut PWR to 50%.
11:39 AM: Hard rolling boil. Cut PWR to 30%.
11:45 AM: Nice rolling boil. Set PWR to 20%.
11:47 AM: Slow boil. Set PWR to 25%.
11:55 AM: Adequate boil.
12:10 PM: Nice boil.
12:20 PM: Nice boil.
12:44 PM: Perhaps a more rigorous boil than needed.
12:55 PM: A bit more boil than required. Set PWR to 23%.
1:05 PM: Adequate boil at flame out (FO).
The volume after FO was about 7.2 gallons at approximately 210°F. The water will need to cool to get a better reading. At the current volume, the boil-off was surprisingly low at about 0.3 gallons over a 90-minute boil. When I boil with the lid off, I usually expect a two-gallon+ boil-off.
I looks like a PWR setting of about 23% will do the work. I am used to using about PWR=60% with lid-off boiling.
3:30 PM: T=150°F, Volume = 7.0 gallons. So, 210°F – 150°F = 60°F delta. 7.2 gallons – 7.0 gallons = 0.2 gallon delta. That’s 0.2 g / 60°F = 0.00333 g/°F.
Predicting the volume when cooled back to 65°F:
210°F – 65°F = 145°F.
145°F x 0.00333 g/°F = 0.483 g
So, 7.2 gallons at 210°F is predicted to be 6.7 gallons when cooled back down to 65°F.
Original volume: 7.2 g
Final volume: 6.7 g
Boil-off: 0.5 g
Boil-off rate 0.5 g / 90 min. = 0.005365 g/min from beginning to end.
Monday, January 28, 2019, 9:30 AM: Kettle T=58°F. Kettle volume = 6.9 gallons. Boil-off loss = 7.5gal – 6.9al = 0.6 gallons.
Now to brew a batch!
UPDATE: 02/02/19: Brewed the my first batch with the lid on the kettle, a maibock at 13.7 Brix pre-boil. Sparged to 6.5 gallons and boiled for 120 minutes at around 23% PWR. I kept adjusting the power until it settled in to a nice boil. After flame out and chilling the wort to 46°F, the volume was right at five gallons. I added some distilled water to get to my target of 5.3 gallons. So, 6.5 – 5 = 1.5 gallons of boil-off over the 120 minute boil. 0.75 gallons per hour. That is substantially higher than the 0.33 gallons per hour I calculated with the water test. Now to see if the beer tastes good.
