Finger Swipe Dosing ==> Sub-Par Shot? - Page 4

by **Fullsack** on Fri Apr 17, 2009 5:55 pm

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.

by **morgan** on Fri Apr 17, 2009 8:17 pm

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."

by **malachi** on Sun Apr 19, 2009 1:35 am

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).

by **miKe mcKoffee** on Sun Apr 19, 2009 3:45 am

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.

by **timo888** on Sun Apr 19, 2009 8:18 am

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.

by **itsallaroundyou** on Sun Apr 19, 2009 9:47 pm

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.

by **dsc** on Mon Apr 20, 2009 8:23 am

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.

by **malachi** on Mon Apr 20, 2009 1:02 pm

The internet is sometimes inaccurate.

by **GVDub** on Mon Apr 20, 2009 1:21 pm

malachi wrote:The internet is sometimes inaccurate.

It can't be!

by **another_jim** on Mon Apr 20, 2009 3:30 pm

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.


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