As an expert sommelier and brewer, I can tell you that the amount of water lost during a 60-minute boil can vary depending on several factors. One of the main factors is the surface area of the kettle. The larger the surface area, the more water is exposed to the heat and therefore, the more water that will evaporate.
Another important factor is the intensity of the boil. If you have a vigorous, rolling boil, more water is likely to evaporate compared to a gentle simmer. The intensity of the boil affects the rate at which the water molecules are converted into vapor.
Atmospheric conditions also play a role in the amount of water lost. If you are brewing in a high altitude location, where the atmospheric pressure is lower, water will evaporate more quickly. On the other hand, if you are brewing in a humid environment, the moisture in the air can slow down the rate of evaporation.
Now, let's discuss some specific numbers. On average, a rolling boil can evaporate between 1 and 1.5 gallons of water per hour. However, it's important to note that this is just a general estimate and can vary depending on the factors mentioned earlier.
To give you a more personal example, I recently brewed a batch of beer using a large kettle with a wide surface area. I had a vigorous boil going for about 60 minutes, and I noticed that I lost approximately 1.2 gallons of water during that time. This was under normal atmospheric conditions, with moderate humidity.
In the brewing community, it's common to measure the evaporation rate of water during a boil to better understand the process and make adjustments if needed. Some brewers even use specialized equipment, such as condensation traps, to collect and measure the amount of water lost during boiling.
To summarize, the amount of water lost during a 60-minute boil can range from 1 to 1.5 gallons, but it is highly dependent on the surface area of the kettle, the intensity of the boil, and atmospheric conditions. It's always a good practice to monitor and measure the evaporation rate to ensure consistency in your brewing process.