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Theoretical question here.

What happens when wort is boiled? Why do we do it? Why is the process not done at cooler temperatures?

My limited understanding, with some assistance from this post and this post, is:

  • Pasteurization
  • Maillard reactions, Melanoidin formation, possibly some caramelization
  • Isomerization of hop acids

But I'm not confident that's the whole story. I know why #1 is important, I can guess at why #2 is important, and I assume #3 is important because all homebrewing instructions tell you to do it.

The genesis of my question is the discovery of this little beastie: http://www.williamswarn.com/

(I have no intention of buying one. It's just an item of curiosity.)

The kits they sell include LME (presumably pre-hopped) and DME, with dry yeast. The instructional video on the home page show the procedure as putting hot-but-not-boiling water in the machine and then adding the extract and the yeast right on top of it before closing the lid. No boiling of the malts at all. That generates the question: why is wort boiled?

One would presume that these extract kits are pasteurized, removing that part of the boil equation. Digging further in the web site reveals recommendations for doing partial mash; steeping specialty grains and hops (in separate pots) before adding to the machine. There's even a reference to all-grain brewing, assumedly a mash conducted before adding wort to the machine, which led me to the conclusion that the WilliamsWarn is not a brewing machine per se, but rather an automated fermenter with integrated carbonation and serving. But I digress.

So what is the difference in procedure between a normal homebrew process and this machine which allows them to get away without a boil? What purpose does the boil serve us?

Hard facts, assumptions, and wild speculation welcome.

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up vote 6 down vote accepted

You've covered the main reasons that I could think of off the top of my head, ie, pasteurisation, flavour formation and isomerisation of hops. A quick search reminded me of the other two, which is that it drives off unwanted volatile compounds (eg, SMM - the precursor to DMS) and it causes proteins and polyphenols/tannins to bind and precipitate out in the form of hot break. Whilst not being a reason per se, but more of an added benefit is the fact that it also concentrates the wort, thereby gaining efficiency that is lost to sparging.

All of those additional benefits would also occur during the production of pre-hopped extracts. Those pre-hopped extract cans are pretty much the standard entry point in the Australian homebrewing scene, and presumably New Zealand too, which is where that bit of kit is made.

Edit: There's a fairly comprehensive article on the reasons for boiling on www.byo.com.

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Phenomenal article. Thanks for the link! – Zac B Jun 17 '12 at 17:21
The article does answer my questions. Thanks! – Galapagos Jim Jun 18 '12 at 18:42

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