German Brewing

Peltier plates are also an interesting proposition. https://en.wikipedia.org/wiki/Thermoelectric_cooling

One doesn't need to bring it down immediately, if it's within several hours then the results are still very good indeed. At 80C the hourly diffusion rate of oxygen into wort is at 3mg/l, whereas at 45C it's merely 1,2mg/l -- which is already quite close to the oxygen level you need for trouble free fermentation (8-9mgl) anyways.

By using a slightly better heat exchanger, a controlled pump speed (one doesn't want to pump full speed through this one for maximum effect), as well in combination with a Maxi310 (which sports a rather large ice-bank), I can bring 50l of hot wort from 95C down to 5C immediately. This runs straight into the fermenter from the kettle. Note that this is more of a convenience, rather than a necessity though. I'd quite happily bring it below 20C and chill it for a few hours if necessary.

That's why I bought a DO meter 5 years ago. It's to control oxygen levels for my yeast. I still think that for well controlled fermentation, people need one.

Weizenberg's Heat Exchanger

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Question for those of you with more complex systems, including lots of transfer lines, HERMS coils, pumps, plate chillers, etc:
How do you CO2 purge all those lines before sending your wort through them? I assume you do, otherwise it would seem a ripe opportunity for O2 intrusion, but I just don't see how you accomplish it.

I bleed them. You really need to bleed all your lines. you can then push the remaining water out via a sample valve on the top-ends and stop once the wort appears, you you can use degassed water. Either way, if you don't bleed then you will ensure you get that oxygen mixed into your wort rather efficiently