Originally Posted by Mr_T
I am just starting out. Brewed a couple of batches ad-hoc, now trying to learn. Reading how to brew. A dumb question, when calculating required water it is mentioned that the contraction of water when it cools off can be added in to the calculation.
If you are measuring using tap water that is pretty cool, doesn't the water expand and then contract back down again? So why would you need to make any adjustment for this?
Yes, water expansion plays a part, because you're reading levels of water at various times of the process, and at various times of the process the temperature of the water is different.
For example, at the end of the boil, the wort is around boiling, and thus, your readings are going to be about 4% higher than if you sat around and waited for that wort to cool. So if you want 11 gallons of wort going into your carboys, then you need to get around 11.5 gallons of wort at the end of your boil.
After you're done mashing and sparging, you're going to want to hit a certain volume, and the wort at that time is around 150°F, and water expands around 2% at that temp. So if you're looking for 13 actual gallons of pre-boil wort, then you need 13.25 gallons of measured pre-boil wort.