Why cool wort before adding to cold water??

So I've seen both methods in instructions and in online forums. In some cases it is recommended to cool the wort down to 70 degrees before adding it to the primary, which takes a long time. In other cases it is recommended to add the wort to three gallons of cold water, and then wait for the whole thing to be a 70 before pitching yeast. In most cases it is at 70 degrees as soon as I add the wort to the water.

So if I am using a plastic bucket for a primary is there any reason to wait for the wort to cool before adding it to the water in the primary? Obviously adding it to water is much faster.

Can someone explain why in my situation I would wait for the wort to cool by itself?

Thanks!

I think cooling the wort first is recommended for 3 reasons:

1) The faster you cool, the better cold break you'll get. This will help with the clarity in the final beer.

2) If you're using a glass carboy (which you aren't) a rapid temperature change could crack it

3) To prevent hot side aeration (HSA). I think there's a bit of a debate over HSA being a valid concern, but the basic idea is that you don't want to aerate the wort until it's cooled. Pouring it into a bucket will certainly aerate it.

http://www.brew-dudes.com/hot-side-aeration/124

It wouldn't make a noticeable difference. What matters is that you cool the wort as quickly as you can (to reduce dms potential) in the most sanitized way you can to the lowest temp you would want for your yeast. The more crucial factor is fermentation temperature for the first 48 - 72 hours.

Fwiw when I extract brewed I use to dump my hot wort on ice to cool it did that for over 40 brews with no ill effect ymmv Chopps

I think a big consideration is control. You can cool the hot wort using chillers and such but once its in a carboy you are pretty much at the mercy of ambient temperature diffusion. I guess if you are using a bucket as a fermentor you could still use a chiller.


Also, I don't remember thermo very well, but it might take less energy to cool 3 gallons of hot wort than it would to cool 5 gallons of Luke warm wort. Just a hunch. Someone check this?

It is really a combination of both.
What is important is to be 70, or below (I go for mid sixties) before adding the yeast.
I do my primary fermentations in the low to mid sixties. I have read, and feel, that this produces the minimum of off flavors.

For the few batches I've done, I try to rapidly cool the wort to 80 or 90F, then add the cold water which finishes taking it down to 70F or so.

I agree that the most important thing is just getting your final product to 70F relatively quickly for pitching yeast. That said, either method can work.