Information regarding a brewing experiment conducted by NCSU statistics students in Fall 2012.
Protocol
Materials: Two Wyeast Direct Pitch Activator yeast packets (Extra Special Bitter and Belgian Saison), five-gallon kettle, propane burner, Campden tablet, 10 pounds dry malt extract, hops, cooling apparatus (copper coil, tubing, pump, trash cans), siphon, Venturi tube, plastic tubing, wine thief (pipette), twenty-four 22oz bottles, syringe, scissors, rubbing alcohol, balloons, foil, stirring spoon, distilled water, spray bottle
The yeast packets were activated a few hours before brewing. A kettle was filled with 5.5 gallons tap water. The water was treated with one half of a Campden tablet for dechlorination. The water was heated to boiling using a propane burner. The heat was shut off, and 10 pounds of dry malt extract were added. The wort was heated to boiling again, and several grams of leftover hops were added. At some point the kettle boiled over, dousing the flame. We didn't notice that the burner went out and so the wort sat slightly below boiling for several minutes. The burner was turned back on and the wort was boiled for about thirty minutes, during which time more leftover hops were added. The wort was stirred and sprayed with distilled water to control the boil. Fifteen minutes before the end of boil, a sanitized large copper coil was placed in the wort to sterilize it before cooling. At the end of the boil, the propane burner was shut off and cold water was pumped through the coil for several minutes to cool it. When the temperature dropped below 75 °F, the cooling apparatus was removed and the kettle was placed on a counter inside. The wort was racked into a sanitized bottling bucket using a siphon, and a Venturi tube was used to aerate the wort. Twenty-four 22 oz bottles were filled with wort up to the bottom of the neck of the bottles, to leave room for krausen. Twelve bottles were randomly selected (using coin flips) for one yeast strain and marked, and the others were fermented with the other yeast strain. The yeast packets were cut open, after wiping the packets and a pair of scissors with rubbing alcohol, and 8 mL yeast was pitched into each bottle using a sanitized syringe. Initially some of the bottles were covered with balloons, and a few were covered with aluminum foil (because we ran out of balloons); the next day the foil was replaced with balloons. The foil sheets and balloons were all punctured with a thumbtack to allow CO2 to escape. The bottles were placed in a refrigerator to ferment; the temperature controller was set to 63 °F, but the beer appeared to maintain a temperature of 70 °F, still well within the acceptable temperature range for the yeasts. (The discrepancy may be because the sensor was taped to a larger carboy in the fridge, not to the small bottles, and the sensor was also configured to allow a few degrees Fahrenheit of temperature variation.) The original specific gravity was measured and recorded, along with the temperature at the time of measurement, using leftover wort. At various points during fermentation, the temperature and specific gravity of bottles (randomly selected using a twelve-sided die) were measured and recorded.
Data
Specific gravity is the ratio of densities of a liquid and a reference liquid. With water as a reference liquid (normally the case in brewing), water has an SG of 1.000; a liquid with an SG of 1.500 is 50% more dense than water, 2.000 is twice as dense, and so on. Unfermented wort has a higher SG than water, and ethanol has a lower SG than water, so when brewing beer, SG starts high and decreases as fermentation proceeds.
SG measurements are temperature-dependent; John Palmer's table was used to adjust the measurements.
To convert SG to percent alcohol by volume, let o be the original gravity and f be the final gravity; then 131*(o-f) is the percent alcohol by volume. For our beer, for example, at the last measurement the saison-yeast beer was at ~3.6% ABV and the ESB at ~8.2% ABV.
Original gravity: 1.088 at 76 °F (24.4 °C). Equivalent SG at 15 °C: 1.090 (+0.002). Measured 2012-10-23 17:00.
All readings below at 70 °F (21.1 °C). To get the equivalent SG at 15 °C, add 0.001.
2012-10-28 21:30
ESB: 1.050, 1.046, 1.032, 1.046
Saison: 1.070, 1.070, 1.070, 1.071
Adjusted:
ESB: 1.051, 1.047, 1.033, 1.047
Saison: 1.071, 1.071, 1.071, 1.072
2012-11-01 24:00
ESB: 1.035, 1.025, 1.030, 1.039
Saison: 1.063, 1.060, 1.065, 1.064
Adjusted:
ESB: 1.036, 1.026, 1.031, 1.040
Saison: 1.064, 1.061, 1.066, 1.065
2012-11-04 24:00
ESB: 1.025, 1.030, 1.026, 1.026
Saison: 1.062, 1.062, 1.063, 1.060
Adjusted:
ESB: 1.026, 1.031, 1.027, 1.027
Saison: 1.063, 1.063, 1.064, 1.061
