What if someone boils away 75% of the wort, can they simply add it back in cold water with no consequence?
You're not boiling 75% of the wort away, you're boiling 75% of the WATER away, the sugar is just going to be more concentrated, and therefore the density, or GRAVITY is going to increase, by EXACTLY the amount that that amount of water added back or DILUTING you boiled away.
Think about it like this, but the numbers are pulled out of my ass.
If a 5 gallon batch of x beer is supposed to be 1.030 but you boiled away a half gallon extra of water so rather than 1.030 your beer is 1.040. That 1.040 gravity is because the wort is now a half gallon THICKER or actually denser, than if that water was in there still.....so in order to regain that gravity, you simply have to dilute that wort by the amount of water you are missing.
Go to
this gravity calculator and you will see what I mean. I think the bottom one would be the applicable one. I like the one on beersmith better.
A can of extract undilluted like in a cooper's can has an insane gravity and IBU (If you read this post I talk about the IBU's of a can of prehopped cooper's extract, because new brewers get panicky when they read on the website the IBU list for the extract,) but when you add water you are dilluting it all down to a resonable amount.
If you add too much water the gravity will be low by that amount as well, so you have to BOIL AWAY that amount and the gravity/density will restore as well.
Even all grain brewers do this if they under shoot or over shoot their boil volumes, and consequently their gravity, that's why refractometers are so great to measure pre fermentation wort. A lot of times you're adjusting as you go along, like if you're brewing outside on a windy day and that normal hour boil where you usually get only a gallon of boiloff you get a gallon and a half..... Beersmith can show you what pre-and post boil gravities should be, so you can see if you're off during a boil, especially if you have a measuring stick or measurments etched on your kettle where you can see how much you're boiling off. If it's too low and you have too much wort in the kettle still, you boil a little longer, if it's too high and your down, you can add water in the kettle or you can wait til you rack over just like a top off batch.
And you won't really notice the difference in the end. It's a pretty common occurance, that's why most software has a dillution tool to begin with to help you figure it out.
