Elbasso wrote:I am puzzled by headspace. Many baristas at the 2008 WBC didn't seem to care about it. They were overfilling big time and then using the Stockfleth's move.

Perhaps this is another situation that is bean + machine dependent?

malachi wrote:Are we all so sure that the "must have Xmm headspace" argument is both correct and universal?

I think you'd get an argument from a number of people on it being correct (George Sabados for example). And you'd get an argument from a LOT of people on it being universal.

I don't think I can say with certainty anything is correct, but I know for certain beyond grinding coffee and adding hot water, nothing is universal.

I think I read a link you posted about the Sabados studies on a different thread, IIRC something about either dosing to the point that the expanding coffee cake forcefully contacts the dispersion screen, or that it contacts the dispersion screen when the PF is locked in, resulting in completely even extraction due to little or no space allowing for the water to penetrate the cake erratically. I am not totally clear on it and I apologize if I am completely off the mark.

At the time I was using a 17.5 or 18 gram dose and was getting heavy screen impressions, and tasty thick bodied shots. But at those doses, with my machine, I would nearly always get an extraction that started at the edge of the basket and quickly fill to the center, never once would it start totally even across the surface. I interpreted this as a donut start and down dosed until it subsided. Maybe it was just a negative side effect of a naked PF used with an untrained eye, mouth, and brain.

I have been able to get very even starts and equally tasty shots at the lower dose with the added headspace, just not so heavy on the chocolate as the higher dose. I still get slight screen impressions but nothing like at 17.5. Since I can get enjoyable balanced shots at both doses, and one starts very even and the other does not, I am left scratching my head. How can there be an optimum dose if I can get well balanced shots at 2 totally different doses, with and without headspace? The more I read and the more I apply what I read, the only certainty I find is that there can only be general guidelines. This makes my brain hurt and I want to go cry.


Gus

The head space theory, as sketched out by Marino Petracco, basically says the puck does not form a proper percolation cake if it gets compressed by the shower screen, and the result is a relatively underextracted shot. The theory works well for some machines. Everyone who's used an Elektra agrees the shower screen is the third rail, ruining shots. The same is nearly as true of the Cimbali group.

But I'm beginning to think that while there are some groups that tend to underextract, like the Elektra or Cimbali, so that they need lots of headspace; there may be others that tend to overextract, and which need to get their pucks compressed for a balanced shot. Perhaps the LM or DC groups are in this category. If this is true, any competent barista, going by taste, will eventually end up leaving leaving lots of headspace on an Elektra or Cimbali, while updosing on an LM or DC.

In other words, the puck expansion theory might be perfectly correct, and because of that, you may not want pucks to expand on groups that are already overextracting.

If this is true, there is no general purpose "basic drill" for baristas, rather, there's becoming experienced on specific machines, and then becoming experienced on enough different ones to keep an open mind when taking on a new one. While that is wonderful for people who are into espresso and widely experienced; it would make a newbie's life a lot harder.

Perhaps it would make sense to instead say that (as a guideline)...

There are machines that desire (require?) sufficient headspace.
There are machines that do not.


You could extend this to something like...

There are coffees that seem to perform best with the high dose/coarse grind approach. If you're on a machine that desires (or requires) headspace, you might not enjoy these coffees.
There are other coffees that seem to perform best at low doses. If you're on a "headspace" machine, you might want to focus on these coffees.


You could even go as far as saying...

Low dose coffees pulled on a "headspace" machine produce a specific type of flavour/experience. If this type of experience is what you desire - you should buy one of these machines, and source these coffees.
If you're looking for the flavour/experience of the high-dose non-"headspace" coffees/machines - you should not buy a "headspace" machine.


If this makes sense (or at least the starting point does), then it would be wise to create a list of machines that fall into the "headspace" grouping. I've never worked on an Elektra, but it sounds like that is one of the machines. I've worked on a couple Cimbalis, and the ones I've worked on have seemed tolerant of high doses (though I've not worked on any home Cimbali machines).



On a side note... when we talk about the results of dose, etc I think (as implied by Gus' post above) we should stick to the results in the cup, rather than being distracted by visuals (be they so-called "puckology" or visual indications from a naked portafilter that are not diagnostic for taste issues).

another_jim wrote:The head space theory, as sketched out by Marino Petracco, basically says the puck does not form a proper percolation cake if it gets compressed by the shower screen, and the result is a relatively underextracted shot.

Can you give us the relevant quote? Is it in Illy's book? I'm looking in the Percolation chapter and see where he says insufficient head space "may cause the deposit of solids into the cup." He also says that thicker than normal pucks require a coarse grind which results in underextraction. But I don't see where he makes a connection between head space and underextraction.

Oops, I guess it's just me unconsciously joining the dots

malachi wrote:Perhaps it would make sense to instead say that (as a guideline)...

There are machines that desire (require?) sufficient headspace.
There are machines that do not.

Identifying which machines are which would be a good first step. The essential next step (for some of us) would be to figure out the WHY. It can't be that hard; there are a limited number of variables.

It could be that some machines, with a change in something relatively simple (a showerscreen design, for example) might be converted from one "type" to another.

Hi guys,

I'm just curious what proof do we have that the puck actually expands DURING the shot not afterwards when the pressure is released? Anyone seen this happening?

Regards,
dsc.

The puck does not expand during the shot.
It compresses.
There is copious research on this topic.
There is also research indicating that coffee particles expand during the shot.

malachi wrote:The puck does not expand during the shot.

malachi wrote:There is also research indicating that coffee particles expand during the shot.

i'm confused.....are you making a point that both statements above are true, or is one true and the other false?

as a beginner, i have inundated my brain with tips and tricks. i eventually found a combo of all of them that produces good shots (by my standards on my machine). without the tips from the experts, i would have gone Office Space on my machine long ago.

but still, my skills definitely need refining, which is why i continue to read posts about technique. however, after reading countless posts/threads about how to get the best shot, nearly all end up in a "well this is what works for me" conclusion. and that's just it, with all the variations out there (bean type, roast type, amount of grinds, last scale calibration, tamp pressure, tamper style, grinder setting, grinder brand, basket brand and size, machine, machine settings, water quality, phase of moon, favorite color, etc...) there is no way, short of getting everyone together with all of their gear in a lab and hammering out the finer points of technique (which would be cool, but not really feasible), to devise a drill that will work for all without variation (if there was, producing coffee drinks would be much less fun). its safe to say in this case, that there's no substitute for experience (and thank god there are experienced members sharing their wisdom here!)

so if people share what works for them, and others experimented with those tips under their particular parameters, then we can/will all inch (or in my case leap) towards producing those elusive God shots more consistently. ok, i'm outta breath now...

I've been having success with finger swiping, using a rolling finger motion that leaves the grounds concave in the basket and removes 2-3 grams of coffee. Would be 15 grams, if leveled with a straight edge, 12-13 grams after the concave move. It's a variation of the finger sweep on Abe's Versalab thread, but it has also been working well with a Mazzer Super Jolly and a Zassenhaus knee mill. I'm playing around with a back and forth swipe that starts a little in from the edge of the basket and also a N,S,E,W version, instead of just a single swipe. No claims about these methods yet.

I am far from the level of expertise of some of you here, but it seems to me that if you asked a dozen trained baristi selected at random what is the best method to dose, level and tamp off a shot, you're likely to get 14 (not a typo) different answers.

A word of advice a wisened old italian barista once told me was "Use what works, and throw away the rest."

itsallaroundyou wrote:i'm confused.....are you making a point that both statements above are true, or is one true and the other false?

coffee particles != puck.
a puck can compress while particles expand quite easily (the puck becomes smaller in volume while each particle that makes up the puck expands).

malachi wrote:coffee particles != puck.
a puck can compress while particles expand quite easily (the puck becomes smaller in volume while each particle that makes up the puck expands).

What Malachi says is true yet might sound confusing. As I understand it during the shot the puck is under pressure making it possible for the puck to compress while at the same time the particles are saturated with water and expand.

itsallaroundyou wrote:i'm confused.....are you making a point that both statements above are true, or is one true and the other false?

The coffee bed's density increases as it becomes saturated with water and the irregularly shaped particles swell and interpenetrate one another; and the density increases all the more as the swelling bed of interlocked particles is subjected to pressure, resulting in a smaller bed volume as it is compressed.

Of course, solids are being removed from the bed during the extraction, so llly refers to the "time-dependent geometry" of the puck.

ok, makes sense in terms of density and volume since both compression of the puck and expansion of the particles is happening simultaneously. i was (incorrectly) thinking of the events as temporally separate and mutually exclusive.

Hi guys,

so the pucks gets more dense and is compressed during the shot. Where did the statement 'the puck expands during the shot' come from then? I heard multiple times on these boards that some machines (Elektras for example) like to have more head space for the coffee to expand during the shot and thus don't like overdosing.

Regards,
dsc.

The internet is sometimes inaccurate.

malachi wrote:The internet is sometimes inaccurate.

It can't be!

dsc wrote:so the pucks gets more dense and is compressed during the shot. Where did the statement 'the puck expands during the shot' come from then?
dsc.

Yes, the internet is inaccurate, but not in the way Chris thinks.

M Petracco in Illy's Espresso Coffee

7.5.1 Ground Coffee Portion ... "Maximum (dose) values are often encountered in home brewed coffee, as the host inclines to overdose to offer the guest the best possible coffee cup. This practice is risky because, as will be seen in 7.5.4, an excessive amount of coffee does not permit sufficient puck expansion during cake wetting."

7.5.4 Cake Shape ... "An important phenomenon to be taken into acount when considering the shape of the cake is the expansion of the bed due to swelling of coffee particles when wetted .... During expansion, the wet coffee grounds exert a pressure comparable to wooden wedges used in the past to cleave stone (highlighting added by me) ... On account of this behavior, an empty space is left over the coffee cake"

The idea that the puck compresses under pump pressure is "barista hearsay lore" based on a post on PF net or some such that someone somewhere saw a glass PF and that the puck got smaller except at the end, when the 3 way whoosh expanded it. I hate to quarrel with imaginary glass portafilters, but as the quote asserts, water and hence water logged coffee particles are incompressible, and also the pressure gradient on the puck is very small, since most of the drop in pressure occurs at the bottom, where the fines are. In other words, the compression force of the pump is small, and the expansion force of the waterlogged particles is huge.

So on the internet, hearsay and peer reviewed information seems to get inverted.

This is not to say that this Petracco chapter is gospel; it has some very big inaccuracies. Puck expansion does account for the greater technical difficulties and skill levels required for successful updosing. A low dose puck is not locked in place, and the breaks and gaps that cause channeling heal themselves during the shot. Overdosed puck's particles are locked into place and gaps do not repair themselves.

But according to his account, there is no such thing as successful updosing:

" ... disturbs percolation and causes the deposit of coffee solids in the cup"

Vague as this is, it isn't true about properly updosed shots.