Keg Beer Pressure in the UK

Regulators with gauges

I am heard to say, with increasing frequency:

The UK is a decade behind the US in keg beer dispense.

Yesterday an American friend of mine responded to this with a scoffing “… at least.” Maybe I should start saying it is decades.

This comes to the fore more and more often lately as I deal with customers who’ve had “craft keg” installs that are, frankly, not fit for purpose. There are multiple factors to this and multiple “WTFs” I’ve seen in installs. But this post will focus on pressure.

I am not a “qualified” cellar-build person. I’ve pondered doing the course but I gather it is basically just a how-to-plug-the-bits-together, that’ll be £1000 please, here-have-a-certificate. The only qualifications I can claim are practical experience, a hell of a lot of research & reading, building bars, getting many varied keg beers pouring, and – probably most important – a sufficient background in physics. (I’m not talking physics major or anything, but I studied some physics through to university level and gas behaviours, flow, dissolvability, etc, are all fundamentals.) I’ve spoken to qualified cellar installers and, so far, not met one who knows anything about vols of dissolved CO₂ in beer. I guess you don’t need it if you’re always setting up to serve unchanging Foster’s et al in a 12°C cellar to standard parameters. (Cellar/keg temperature is another issue… deserving of a large post of its own.)

Everything changes drastically when it comes to “craft beer”. It’s not all just pasteurised lager with a “standard” 2.2 vol CO₂ (or whatever it is) – suitable for a one-size-fits-all sort of configuration. It is *part* of the definition of some beer styles that they are at certain carbonation levels, and your top-pressure should be set accordingly. And then there’s KeyKegs, another ballpark – another game – entirely. If you have just one “craft” line for keg you’ll probably find yourself switching between KeyKegs and top-pressure kegs. (One reason many UK craft brewers are keen on KeyKegs is that it is less likely that crap cellar installs will cause their beer to be served under- or over-carbonated, KeyKeg basically eliminates one piece of fine-tuning at the pub end of things.)

What this boils down to is: every beer line should have a dedicated secondary regulator, and every secondary regulator should have a pressure gauge on it. (And the primary should have an out-side gauge allowing a safe maximum line pressure to be set (<50 PSI, <45 for Pet*cough*crap*cough*ainers) – albeit this can be set once at install and the gauge not needed. But the gauges aren’t an expensive upgrade and it is a useful bit of info when debugging cellar issues if you don’t have a pressure checking gauge handy.)

KeyKeg dispense flow chartTo add some credibility I’ll point you somewhere else at this juncture, go have a look at what Magic Rock, one of the UK’s top modern breweries, have to say about KeyKeg dispense: KeyKegs, differences & dispense issues…

So – what happens when you want to follow Magic Rock’s advice and have no gauges? You’re buggered is what. I’d not touch the thing, as you have no idea what the pressures are you could well take it past the safe limit.

But say you do take the risk and nudge it up a bit. That keg runs out. You want to put a normally carbed top-pressure keg on, you switch couplers, connect up. Over the next 2 days that beer gets increasingly carbonated and the last third basically pours foam. Bugger.

IF THERE ARE NO GAUGES SIMPLY DO NOT EVER TOUCH THE REGULATORS.

Jolly Good Beer wall

Jolly Good Beer wall

Folk in the US with these “Flux Capacitor” setups aren’t spending all their money for shits and giggles. The kit on display is normally in the cellar/coldroom – putting it on display is a bit of marketing really – but the reasoning behind it is to highlight that these things are actually important & the bar takes it seriously. Albeit it does concern me a little, pressures should not need fiddling with – pressure should be set suitably for beer being plugged into the line and then that stays the same until you’re done. I think that functionally the kit is better off in the coldroom. But hey, it makes a good talking-point. This inspired me to put regulators on the front of my own mobile bar. (Although there are other good practical reasons for that, the front of the bar is easy to get to compared to the back through a stack of kegs and tangle of lines.)

Shiny new "craft keg" install... wot?! No gauges?!

Shiny new “craft keg” install… wot?! No gauges?!

In this calendar year I’ve come across 5, *FIVE*, new keg installs that had no pressure gauges on the regulators. THREE of these were done after I told the folk getting the installs to ensure they had pressure gauges on their regulators. In the most recent case I was multiply-insistent. But on the day these professionals were adamant this was not needed… and in the end: no gauges. One of the 1st kegs put on the system was a KeyKeg, which was triggering the fob detector, and needed the pressure increased. Yet these professionals told the customer that my advice to them was wrong, that I didn’t know what I was talking about. (Oh, and this setup has kegs at ambient temp… *grumble* … but this means even more need for pressure adjustments! More chance of fobbing.)

So… in an attempt to basically explain that the professionals don’t have a sodding clue: here are some guidelines for the different kegs out there…

KEYKEG (and other bag-in-container type pressurised kegs)

Slimline KeyKegs stack nicely.

Slimline KeyKegs

The great thing about KeyKeg is you cannot screw up the carbonation of the beer with top-pressure. Hell, you can use compressed air and save on the cost of food grade CO₂. (It’s up to the brewery to screw up carbonation, it does happen, too often… usually to the over-carbonated side… in which case KeyKegs can be vented.)

I can offer no better advice on KeyKeg to what Magic Rock have published. So pop along to their website to get the low-down on this topic.

The only addition I would make is that I tend to run KeyKeg at 35 PSI by default, and this works in almost all cases. If needed I will increase pressure up to 45 PSI. If you need more than 45 PSI then your beer is either over-carbonated or the keg is too warm. (And KeyKegs are rated for a maximum of 51 PSI… NEVER EXCEED THIS!)

TOP PRESSURE KEGS

Top-pressure kegs

Top-pressure kegs

This is where the real problem with some of these keg installs lies.

In light of hitting issues so frequently I have derived my own CO₂ pressure chart. As you do. De-rusting some of the old physics in my head in the process… the key differences between this and most other charts I can find are a) it is in Celsius and b) goes above 10°C… given UK cellars are often at 12°C this is somewhat essential. (Oh, and events, ah good old craft beer events, they’re another ballgame entirely.)

The 12°C cellar makes us in the UK a bit of an outlier really, here’s guidelines for cellaring Schneider Weisse: Draught Beer Guide – note that their pressure chart maxes out at 7.5°C… well, if you want to set the correct pressure for Schneider Weisse in a UK cellar look up 12°C against 3.5 vol CO₂ here:

(Oh, and I’d double-chill the Schneider Weisse… ever wonder why UK pubs have such a nightmare of a time pouring this stuff?)

But wait, there’s more! There is stuff all information online regarding mixed gas. The prevalent use of 60/40 mixed gas in the UK is what I call “the great beer flattener” – systems seem often configured just to provide dispense pressure with no mind to carbonation level. You need quite high a pressure to get 60/40 dispense working perfectly for well carbed beers in a 12°C cellar. If you’re using plastic kegs then I would highly recommend against 60/40 gas as most kegs are rated to about 50 PSI and I personally limit them to 45 PSI. Pressurised plastic beer containers have caused injury. This chart was a bugger to derive, all I could find online was an Draught Beer Quality guideline update that is worked out for a maximum temperature of 4.4°C… in the UK? Hah! So I had to get my head around partial pressures to adjust the pressure formula, to give us:

(Any “peer review” of this would be much appreciated.)

It should be kept in mind that if you smash through kegs in 2 days then carbonation isn’t going to change much and pressure is a lot less of a matter. You may even get by with plain N2 if you’re draining kegs fast enough (NOT RECOMMENDED!) and I’ve heard of some setups using compressed air like at GBBF (REALLY NOT RECOMMENDED!!). However it is my observation that in your typical multi-tap bar kegs can linger on a line for a week or so. This is not ideal… but it makes using correct top-pressure an essential part of the beer quality formula.

In the US there is this thing called “Certified Cicerone“, it is sort of an industry qualification. And it isn’t trivial like the UK’s BIIAB ABCQ. I’m planning on doing the Cicerone exam when the opportunity arises and understanding pressures is a part of the syllabus [PDF].  (I’m a “Certified Beer Server… but that’s just an online multiple-choice test.) In fact in my opinion one of the best things BrewDog is doing for keg beer in the UK is putting many of their staff through Cicerone training and qualification. (Some of these staff are leaving BrewDog and spreading through the industry – taking their knowledge with them, this is great for everyone.)

The DraughtQuality.org website – a resource created by the US Brewers Association – is also a mine of technical information. (And key to the Cicerone syllabus.) This PDF for example is a much better overview of carbonation than my own ramblings: Understanding Dispense Gas [PDF]

Have I presented enough evidence to make it clear why being able to set the pressure level of your gas is essential if you want to serve different & varied keg beers through a beer line?

If not… what do you think. Why not?


Jolly Good Beer – putting the science in dispense!

Or maybe: Jolly Good Beer – putting the SENSE in dispense! ;)

#1: Do not exceed rated keg pressures…

What is this “natural” you speak of?

I’ve long been meaning to do a detailed write-up about beer packaging, so I have one place to point people to who’re somehow confused and have odd ideas about about “keg”. A poor and quite misunderstood three-letter-word is “keg”, and to be honest “cask” is pretty misunderstood too. I don’t have time to write that post… but I can address one aspect of the the pro-cask FUD that comes up frequently. The use of the word “natural” with respect to beer. To cut a long story short: it is pure propaganda.

What is “natural beer”? I think I can pick off a few obvious items that may make some people think beer has lost its “naturalness”:

  • Pasteurised – a process of heating the beer to ensure it is sterile – i.e. the yeast, and any other organisms that may change the beer are killed. Heating will of course change the beer in other ways as well, some volatiles (hop flavours for example) will break down. Pasteurisation is great for stability but perhaps less great for flavour. Stability? Well, perhaps not… live yeast has a known protective quality. It will sit in your beer and “mop up” some excess O2 thus reducing oxidation. (And no seal is perfect, so as well as helping with any O2 left in the beer after filling this helps with the small O2 leakage through capped bottles and probably even cans.)
  • Sterile Filtered – a different approach to achieve the same end. Rather than killing yeasts/etc it filters them out of the solution. But such a fine filter will also remove some large molecules that contribute to flavour. As for the beer now being “dead” – this has the same impact as described above. (If one of these two have to be used then I’ll prefer filtration… there is another approach: centrifuge. Thornbridge and BrewDog use this… and their bottled products are pretty fantastic.)
  • Contains “chemicals” – contentious. The obvious truth is that all beer is made from chemicals! What I guess we have to read into this in context is the addition of extra substances not normally used for brewing. What are these though? Near all breweries add chemicals to treat their water, malts come with the required enzymes for starch conversion, adjuncts like sugars/wheat/etc are perfectly acceptable for certain styles. So “chemicals” is really a pretty confused area and probably best considered bunkum. Some breweries may use added enzymes to speed up mash/fermentation processes I believe. I know a couple of good breweries adding an extra enzyme to de-glutenise beers without altering their flavour (a great thing for coeliacs!) I think that, like the word “natural”, the word “chemicals” is an all-too-easy-to-reach-for emotive word thrown around blindly in the whole cask/keg debate. (Were sulphites perhaps once used to stabilise beer?) (Where do finings in cask ale fit in here – isinglass and the various adjuncts used alongside it?)
  • “Extraneous CO2″ – what’s this then? In CAMRA terms it is use, in any way, of CO2 not created by the action of yeast in the beer. This is also a contentious issue. As there is argument even within CAMRA about the appropriateness of CO2 in the cellar. The big question is around aspirators (aka “cask breathers”) which let just enough CO2 into cask to protect the beer from air contact. And air, really, is the worst thing for beer. No good brewer wants you to be drinking oxidised, stale, beer. I go further and wonder what is so bad about CO2 full-stop. But I guess we hit a personal preference issue regarding fizziness here and I’ll leave it at that.

I think those four items are key to what is behind ideas about “unnatural” beer. The first two are ones I personally think are not really in the interests of good beer… and in fact in my book use of either of them is a line crossed. From what I’d consider a “craft” product to one that quite simply isn’t. Does it make beer “unnatural” … sure, I’ll buy into that a bit. It certainly makes it less than it was and, sure, one could say it makes the beer “dead”.

The whole chemicals thing is just puzzling to me. I’d like to know what these evil chemicals are… but I’ve yet to come across them in the brewing world. And as I said – without chemicals you cannot have beer. (Nor life, nor anything really…)

Now, CO2… the point of this post is to show that your ideas of “natural beer” wade into a big grey area in the world of modern brewing. We do have another point often brought up about what makes “cask ale” natural… that is cask conditioning. “Naturally conditioned beer”… i.e. carbonated by the action of yeast in the beer, not force-carbonated by addition of external CO2. So a natural beer is one that is conditioned in the container it is served from and that involves none of the items in the above list (assuming by “chemicals” we’re talking some odd crazy substances used to somehow adulterate the brewing process).

I bring to your attention the humble KeyKeg. An interesting little keg-type device in which beer is contained within a bladder from which it is extracted using pressure (air will do, but often CO2 is used). The important thing to know about KeyKegs is that many breweries who use them put exactly the same beer into them as they put into casks. Live, good, natural, beer. It conditions in the container it is served from. It does not come into contact with extraneous CO2. The only difference between this beer from keg versus cask is that the keg version will probably be served at a cooler temperature and with more (natural) CO2 remaining in solution.

This beer, from KeyKeg, is a fully “natural” product by any wild definition I can think of.

Moving on from KeyKegs… breweries filling conventional kegs usually do so from a conditioning tank where the beer has been “naturally” carbonated. Again. Live, good, natural, beer. Some even let the beer condition in these kegs (Moor, for example). The only point where the “naturalness” may come into question is when CO2 top-pressure is used to expel beer from keg. And frankly… that’s just a bit of an odd viewpoint to have, in my purely personal opinion. CO2 is CO2. The “extraneous CO2″ does not necessarily add “fizz” to the beer – if used appropriately it just maintains the CO2 level the beer is designed to have. That carbonation level has been chosen by by the brewer – it is as the brewer intends it to be. They’ve, naturally, brewed a beer to be served fizzier. You may not like that… but it is still live, natural, beer.

Next step is to swing across to the grey area of “cask conditioning”. Those “conditioning tanks” I mentioned before are used by many breweries to pre-condition beer prior to filling both cask and keg. So again – in all of the above keg scenarios identical beer is being put into cask. The difference is that the keg version has its natural CO2 level preserved by using CO2 top-pressure, and the cask has its CO2 level reduced via venting.

So sure – there are differences… but unless letting “naturally” created CO2 escape from beer to make it flatter is an essential part of being “natural” (really? really!?) then I think you can drop the silly cask-is-natural keg-is-unnatural approach.

(And I’m really really not saying you have to like cooler fizzier beer… I’m just staying stop claiming it isn’t “natural”. This is needlessly emotive FUD that does nothing for good beer except add confusion. If you want to play at politics (aka lying) then go join a political party… what the beer world needs is facts, not bullshit.)

Chemicals, sub-note: is there a finings Elephant in the room anyone? There’s the (emotive) “fish guts” isinglass finings, and alongside these many breweries use various finings adjuncts like silica-gel. There is an argument that these “drop out” of the beer and you don’t drink them. But there’s always going to be some trace of these “chemicals” left in suspension. Justin of Moor Beer also likes to use the word “natural” – in his case to refer to beer that has not been mucked with by adding finings (regardless of what container type the beer happens to be in). I have somewhat more respect for this usage of “natural”, but do prefer simply “unfined”… isinglass is, after-all, simply made from fish and fish are pretty natural.

[I’ve put up an additional post regarding some other iffy statements in the CAMRA article.]

Followup: Cask Ale Fallacies

Well, there has certainly been some interesting discussion out of the “Three Cask Ale Fallacies” post. On the back of some of this discussion some updates have been made to that post (all clearly labelled as such). It is time to post a follow-up I think, rather than muddy the waters by adding more updates to my own post.

Background

There is some discussion worth reading on the Boak & Bailey post.

Clarification

I just want to take a moment to state clearly what I am NOT claiming, and never claimed:

  1. Most importantly: I am NOT claiming that Ed is serving duff beer. I think his process is sound but I challenged some of the methods and justifications. I thought I was very clear in my post that a) I expect Ed serves fantastic beer, and b) I think Ed is the sort of cellar person we need in more pubs.
  2. I am NOT claiming that there is a one-true-way to keep cask ale. This would just be totally bonkers. I just seek to examine the reasons behind certain thinking and practices.
  3. I am NOT claiming that I am an expert on the subject. However, I do consider myself an informed commentator… who is seeking to extend and clarify his own knowledge on the subject.
  4. I am NOT claiming that the general public ought to be aware of any of the technicalities. This is a discussion for people who keep beer or are deeply interested in it. Albeit if I hear “the general public” peddling bullcrap as fact I will sometimes challenge them on it. This most often involves “I’m a CAMRA member” types who’re are proselytizing or trying to “educate”. It happens on the oxygen front predominantly. I suspect I find myself on the receiving end of such education more often than older folk purely because I spend too much time around beer and I’m under the age of 50 (I’m 34, for what that’s worth) and I’m a foreigner (Australian). So it is assumed that I need a proper education in “English beer”. This is usually hilarious… but anyway, I digress.

The conversations coming out of my original post ranged far and wide with all kinds of wild tangents of discussion and heated argument taking place. Even “CAMRA bashing” became the topic at one point. I’m sticking purely to my original points in this post.

1. Oxygen (O2) – needed in secondary/conditioning?

I see my job as the cellarman is to use what the brewer has given me (namely yeast + sugars), add some oxygen, and let rip.

There’s all many of biochemical reasons why oxygen is important – one of the most is allowed aerobic respiration to occur which re-metabolises compounds like diacetyl (produced during anaerobic).

This point hasn’t really been discussed much. I stand by my statement that any requirement for O2 to help/start “secondary” & “conditioning” is a myth.

I don’t know where the diacetyl item comes from… the material linked to in the comments appears to me to claim the opposite. (Find the “OXIDATION” section, it does explain that plenty of oxygen is needed in the wort to ensure a healthy fermentation with little diacetyl production.)

I take it by the lack of discussion on the topic that there isn’t any real technical challenge or counterexample.

With respect to Ed’s cellaring process I don’t think O2 plays any role in the quality of the beer coming out at the tap. When a cask is vented it’ll be ejecting CO2 which will mostly keep air/O2 away from the beer. If the cask is sealed with a nylon peg when it is not active then this ensures O2 continues to stay out of the picture. It won’t be until the beer is served that air/O2 is drawn into the cask as per usual with cask ale. (Where we hit a whole different kettle of fish with respect to the desirability of oxidation to “soften” beer.)

3. “Secondary” (cask conditioning) – does not occur at the brewery?

you say “do any brewers send out beer that isn’t in condition these days though?” Every single one does.

Ever drunk cask beer straight after it’s been racked and tapped? There is no condition in it whatsoever.

There has been a little discussion on this topic but not a lot. I’m standing by my position that _most_ cask beer leaves the brewery with suitable “condition” (sufficient vols CO2) to serve. (Meaning only that there is sufficient CO2, not that the beer is ready to serve… this will depend the beer and maturation required to achieve peak/desired flavour.)

There has been some lighthearted challenge on the use of the term “secondary”. A bit nitpicky perhaps… we all know that it is just a continuation of fermentation, right? And it is common practice to use the term to refer to that phase of fermentation used to achieve sufficient CO2 is in the beer. This “secondary” fermentation might take place in bottle, cask, or tank – and it doesn’t magically cease when the beer leaves the brewery. (Ignoring sterile filtered and/or pasteurised beer of course.)

As for the original point – I fully accept that sometimes beer does leave the brewery without sufficient carbonation. I said as much in my post. There is a variety of reasons for this – the yeast might just be a bit lethargic, possibly due to cold weather, or the brewery might not have given it enough time… and in this latter case I believe it is normal for a brewery to give a warning. It is also not unusual for a pub to reject a beer that does not arrive with a reasonable CO2 level. This has been my personal experience on this subject.

I have asked a few brewers about this in the last week and the uniform answer has been that they don’t let the beer out of the brewery until sufficient time has been given for the beer to reach a desirable carbonation level. (It is an amusing co-incidence that one brewer who I don’t believe was aware of this discussion warned me: you can have this beer but we’ve only just racked it so it will need a week.) The most useful bit of information on the topic I’ve found is a blog post from Jon of Stringers Brewery: Gas, and Hot Air – this discusses tank versus cask conditioning at the brewery, the relevant part of his post is the bit where cask leaves the brewery at 1.4 vols CO2 to be ready for venting at the pub at 1.5 vols CO2 (and will be finally be served below this after being vented).

Why is Ed’s experience of this at odds to the reality? It may be due to venting immediately after shaking the cask… this will cause a violent exit of CO2 from solution. So if you immediately sample the beer from this cask it probably is seemingly flat. However as Ed explains he then gives his beer plenty of time to generate some more CO2 to recover its condition.

My experience of cask ale is that is usually arrives from the brewery well carbonated. It is left on stillage for at least half a day and then vented carefully to try and retain CO2 in solution. Retaining CO2 is ideal for beer festivals, the context in which my own experience lies. I don’t have the experience of a pro cellarman, but I have vented at least 1000 casks in this way across a very wide variety of breweries and beers.

I cannot say whether one or the other method results in better beer. One could ponder that Ed’s violent “whoosh” of CO2 release carries away undesirables – sulphur compounds perhaps that give “green” beer its “Burton Snatch”/struck-match aroma? On the flip-side this could perhaps cause the beer to give up volatile hop aromas that brewers try so hard to keep inside the beer. One for some experimentation perhaps.

2. Yeast rousing (shaking/rocking casks) – is essential for good beer?

This item has been rearranged to be last as it is the “myth” I’m least convinced about. When doing my training I was instructed by a good brewer to *not* agitate casks unnecessarily. I took it as being a strict rule, coming from an experienced chap with a Heriot Watt masters degree. However I’m now thinking this was a “lies for children” sort of instruction… a rule of thumb that hides a hell of a lot more “under the bonnet”.

Where I now stand on this is: know your beer.

The factor that is most important here seems to be finings performance. A complicated subject in which there are several variables to consider (brewery fining practice, chain of supply, yeast properties, beer properties, temperature… at the least). This is why “know your beer” is the rule here.

The main item of interest seems to be performance of finings across “drops”. The feedback seems to go something like: On the first “drop” after the finings have been added to the cask the trub layer will be relatively loose. On the second drop a little tighter. On the third and maybe fourth drops the tightest. After which the finings will start to get “tired” and be less effective. This is the collected anecdotal evidence from several brewers and does not represent a set of hard rules, but seems to be a generally accepted pattern.

If you buy your beer from a brewery that fines their beer when they rack it it would have dropped once after racking. Then a second time after transit to your cellar. Then the third time after you agitate it before putting on stillage. (Unless it has been shaken about additionally along the way!)

If you buy your beer from a distributor then there is probably at least one extra step along the way, likely more! As a new distributor myself I am now ultra-aware of this and will be careful not to move casks unnecessarily in the future.

Obviously there is a vast array of possibilities here. I hear some breweries add finings only when the cask leaves the brewery – so if receiving direct from the brewery it is only on its 1st drop when it hits your cellar. Based on the ideas discussed so far there would seem to be a definite benefit to thorough agitation before putting this cask on stillage.

So, what’s the worst that can happen if you agitate? Due to chain of supply it’ll have been through 6 or more drops and simply won’t clear. (Ever? Or will it just be very slow?)

So, what’s the worse that can happen if you don’t agitate? It’ll be on its 1st or 2nd drop and may not form as tight & small a trub layer as it could – thus you have a higher ullage and you get a lower return on your cask of beer.

There are people who swear by doing it either way… I think perhaps a few more have stated that they do rouse than those who have stated that they don’t. However I’ve not had time to try and find and count all the responses.

Another question is: if a cask has been sat on its end for 24+ hours and you move that cask from that position to being sat on a traditional stillage, what happens to the trub layer and how does it settle without the additional agitation? It was specifically this situation in which I was originally instructed that there was no need to go shaking the cask unnecessary. However that is in opposition to this statement:

I’ve done some searching on the topic but haven’t found anything particularly enlightening. I did find a treasure-trove of interesting beer information along the way however: onlinelibrary.wiley.com – in this I found papers on some experimentation with finings performance: Improving the Effectiveness of Isinglass Finings for Beer Clarification by Optimisation of the Mixing Process. Part 1: Laboratory Scale Experiments (Also: Part 2: Pilot Scale, Part 3: Full Size). But whilst these papers are interesting the context is not right in the context of this discussion.

Ed Wray did a little digging to see if he could come up with any data on the topic and came up with: So no definitive answer yet. I suspect it’s one of those questions to which the answer is “it depends”.

Ed Razzall has used his connections to do a little experiment for us all. He’s going to get two glass fronted casks of Ghost Ship from Adnams and treat them both exactly the same way aside from the vigorous agitation pre-stillaging. This is exactly the sort of thing I love… experimental evidence! I’m looking forward to finding out the results. It will not give us a definitive answer to the “do” or “don’t” agitate question… but it will give us a useful and interesting datapoint.

Inconclusion

As is often the case more questions are raised than answered. I still stand by my original statements with respect to “myths” 1 (oxygen) and 3 (condition). In the case of myth 2 (rousing) we seem to have hit a clash of two differing schools of thought neither of which has any hard evidence to back itself up or shoot down the other side. Whilst the true answer may be “it depends” – I’d like to know why? Because that’s just the sort of person I am.

But I do accept there may be no clear (haha) answer to some of these questions…