A touchy subject Guinness. I wouldn't be wondering if I could make a Guinness clone near to the "real" version, but more like something much better than Guinness (easily achievable) near to the REAL version - which Guinness stopped brewing 60-70 years ago.
All the quirky methods are just tricks created by Guinness to keep making a beer that resembles its past glory but at fractions of the cost. Home-brewers don't want to be copying these tricks, but should be attempting to recreate what the tricks are trying to emulate.
Ive done it. I seem to remember it was a bit more roasty than guinness. Also guinness is supposed to have a 'twang' to it. Which I've read recipes purposely souring a small amount of wort then adding it when you package. Or using acid malt.
You do need nitrogen to get the creamy head
Different temperature yield a more or a less fermentable wort either giving a thinner beer or one with more body
Let us start with Nitrogen. Guinness made a near disastrous move* into 60's keg beer. The high carbonation, acid (carbonic acid from CO2) concoction was not like Guinness at all. Nitrogen was Guinness's saviour where they could still use the high keg pressures but keep the carbonation, and therefore acidity, down. Plus the nitrogen could be got to dissolve in the beer and come out of solution in very fine foam creating the creamy long lasting heads of the real pre-1960s Guinness (needs cold, but a lot of drinkers were moving that way anyhow). They did it to cans too with the famous "widget".
And the "souring"? Back in the 70-80s I'd heard stories that Guinness was once "vatted" (after all it was a "Porter") and purposely infected with Brettanomyces. Export Guinness was still treated that way. Humm. You can still get this export when abroad - but it's brewed in Belgium under licence (and is terrific). Perhaps the idea of adding purposely soured wort goes back to this? I doubt Guinness go to this much trouble for a "trick" to emulate something that they may or may not have done.
The way Guinness created creamy heads pre-keg (and therefore pre-nitrogen) is fascinating. I must get round to attempting to copy this one day. Meanwhile, purely CO2 conditioning (a low pressure) can still produce creamy heads on home-brew stouts.
(EDIT: *Not really true. Just wishful thinking that it would have been disastrous. The UK - and other parts of the world - was already making the disastrous switch to 60's style keg for
most of their beers. Guinness were playing with nitrogen by the end of the 50s, but it was too new and they were keeping it to themselves in Ireland. Unfortunately we were all to end up with it eventually. )
