Water amount question

Is starting a boil with 5 gallons and having one gallon evaporate and then adding one gallon of cold water to top off to your desired 5 gallons in the fermentor exactly the same as boiling with 6 and finishing with 5 gallons for fermentor due to evaporation, or are these two things going to end up with different taste and gravities?

Gravity should end up being the same. Your hop utilization would be different, and you might get slightly more caramelization and Maillard reactions on the smaller boil. So the end result wouldn't be exactly the same. I'm not sure the difference would be noticeable though.

As a general rule I would recommend boiling the 6 gallons down to 5 gallons versus adding the 1 additional gallon of water. This is because you will achieve better hop utilization and a slightly better tasting beer. Either way I am sure that you will still have some kick ass beer.

Also, there shouldn't be any difference in orignal gravity since there should be the same amount of fermentable sugar in both. However, you should always stir your wort really well before you take your gravity reading with your hydrometer. If you dont stir the wort really well then they hydrometer will give you a gravity reading much lower than what it actually is. This is because the extra gallon of water that you added to the TOP of your fermenting bucket is less dense than the thicker wort that you poured into the bucket at first.

Not to mention you'll likely drive off any chlorine that might be in your cold water. (A good thing)

B

Mrclasen said:

However, you should always stir your wort really well before you take your gravity reading with your hydrometer. If you dont stir the wort really well then they hydrometer will give you a gravity reading much lower than what it actually is. This is because the extra gallon of water that you added to the TOP of your fermenting bucket is less dense than the thicker wort that you poured into the bucket at first.

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I've had it go the other way - mainly because I use a bottling bucket and end up with a higher gravity - same reason though, the water doesn't mix quickly so I have higher gravity wort on the bottom I'm drawing.

BTW, if left alone over the ferment time, it would all mix but the OG would be off, so it is in general better to mix it.