Basket size to tamp pressure ?

[espressme]

My question is:
If an applied tamp pressure of 30Lbs (13.6Kg.) is a standard for espresso grind tamping, why is that not different for different basket sizes.

It would appear that the actual pressure per square inch applied to the grind could be wildly variable between machines!

My (possibly mistaken ) calculations are:
45mm basket ~1.8"dia. or ~2.5in.²of area........63mm basket = 2.5"dia. or 4.9in.²area......68mm basket= 2.68"dia. or 5.6in.² area

So, dividing the 30# by the square inches:
45mm basket=12#in.²........63mm basket =6#in.².......and 68mm basket= 5.3#in.²

That seems a ~40% variation of pressure on the grounds.:?


Richard / espressme

[RapidCoffee]

If an applied tamp pressure of 30Lbs (13.6Kg.) is a standard for espresso grind tamping, why is that not different for different basket sizes.

Good observation! Not to dodge the question, but there's nothing magical about the 30# tamp pressure. It's more important to be consistent in your tamping. Many espresso afficionados use a lighter (or heavier) tamp and do just fine.

[timo888]

The wider the basket the shallower the basket, unless it be oversized to permit a larger dose, as many are; less force is required to compact a shallow column than a tall column of coffee. When you compress the grinds, the compacting is tightest near the tamper surface; the grind in the basket gets gradually looser the farther you 'descend' into the puck. And so the depth of the basket and the shape of the coffee column (cylindrical, or one of the conical variations) would affect the quality of the tamp as much as if not more than the diameter of the basket.

Illy remarks that the difference between no tamp at all and even a light levelling tamp is major, but that there are only minor differences between 20 pounds and 40 pounds and you don't start to see major changes again as tamping force increases until you reach ~80 pounds.

I have found the following things to be far more important than nuances in tamping force; nuances in these factors do have major effects:

grind taking into account the age of the roasted bean and humidity etc
dose
the shape of the basket (especially the height-to-width ratio of the puck)
the effective egress as defined by the basket's filter
preinfusion method and duration

A proper preinfusion should reach the grind down near the filter so that this section of the puck expands because of the hydrostatic pressure and presses tightly against the filter wall, which will help prevent channeling.

Regards
Timo

[mogogear]

If you have visited CG lately Mark Prince has a tamp article on the Home page. It is the first of three and makes some very parallel observations about how deep in the coffee puck tamping really effects.

Sorry Dan not meaning to point elsewhere