Lever pre-infusion = way to bring the temp down?

[hbuchtel]

Just thinking, could the tradition of a long pre-infusion on lever machines be primarily a way of bringing the water temp. down?

Meaning that giving the water a chance to rest in the piston-cylinder before pulling the shot allows some heat to be absorbed by the group head etc.

I've been doing a long low-pressure pre-infusion on my Presso, with decent results, but I'm wondering if it is really beneficial to non steam-pressure lever machines (i was really tempted to put a dash between each word . . .).

I'd appreciate any feedback, especially from folks with both types of machines! I'll be trying it tomorrow. (must go roast now . . .)

Henry

[timo888]

Henry,
Illy writes in Espresso Coffee: The Chemistry of Quality that the preinfusion "yields a richer body and better flavor" because extraction is improved by "the swelling of the bed". (section 8.5.9 Cake Moistening)

I've been doing a long low-pressure pre-infusion on my Presso, with decent results, but I'm wondering if it is really beneficial to non steam-pressure lever machines

Preinfusion certainly benefits the espresso also with unpressurized machines such as the Peppina and the Caravel, whose brew water is not too hot and so needs no cooling. That said, if the group of a pressurized boiler is not heat-saturated, gradually bringing water into the group would enhance the group's ability to lower the water temperature.

Illy also writes that "cake temperature" is important (ibid section 8.5.6). Preinfusion presumably would provide some benefits in that regard as well, helping to have warmed up the puck of coffee before the main percolation-under-brew-pressure happens.

Regards
Timo
P.S. Did you receive your Zerowatt

[hbuchtel]

Hey Timo, thanks for the quotes.

Looking at your Peppina method I notice the longer pre-infusion (~17s.) is a sort of 2nd pre-infusion, after the first one, is that right? If you are pulling a single about how long is the pre-infusion?

A single-pull of the lever should draw a gross quantity of water sufficient to net a single shot. (The cylindrical filter basket is Peppina's double-basket; the single is conical.) And so for the double, after you have guided the lever upwards about two-thirds of the way on the first pull to cause the preinfusion -- you will see a few drops and then a syrupy flow for a couple of seconds--you would then depress the lever all the way down once again, allowing more hot water to fill the piston chamber. I keep the lever down so the preinfusion lasts a relatively generous ~17 seconds. The water is at the perfect temperature and so the danger of overextraction is small. Again, however, it all depends on bean, grind, dose, and tamp. At this point, the puck has been infused with water and there's more water at the ready inside the piston chamber. Now simply let the lever rise under its own power to finish the shot.

My thought above came while reading this topic- HX vs Dual Boiler (...), specifically this quote-

Many who hear "flat temperature profile" likely assume that it means just that, i.e., except for the first few seconds, the coffee puck experiences the same extraction and brew temperatures throughout. In reality, the temperature from the top of the puck to the bottom doesn't converge until the last seconds of the extraction, and of course the brew pressure spans the range of 9 bar at the top of the basket to atmospheric pressure at the exit.

Which brought up the following questions,

1. Does the temperature of the pre-infusion water affect the taste much?

(I've been struggling with some nastiness in my Presso shots recently)

ie In a Pavoni for example the water slowly soaking the puck during pre-infusion will be at a higher temperature then the pre-infusion soaking in a Peppina (or my Presso). Does this mean Gravity-levers etc would benefit from a shorter pre-infusion?

Is pre-infusion important as a brewing step? Does the coffee extracted during pre-infusion affect the taste in the cup much?

2. Perhaps the tradition of a fairly long (~10s.) pre-infusion is as much to lower the brew water temp. as it is to condition the puck?

If so, then non-steam-pressure-lever-machines (whoo-hooo! dash-madness) would probably want a different pre-infusion pressure-profile. (for example, a couple second ramp-up to full pressure, rather then a long ~1 bar pre-infusion then full pressure.)

END speculation

Well I got promising results this morning from a short pre-infusion, although it was drowned in milk as is my morning habit.

Just to be clear, what I am comparing is a gentle ramp-up to full pressure (~2 seconds) vs Pavoni-style ~10 second ~1 Bar pre-infusion, then full pressure on a warmed up Presso (similar to Peppina/ Caravel etc).

Thanks for your thoughts!

Henry

[timo888]

PEPPINA PREINFUSION
In the Peppina, when the lever is depressed, the piston retracts and water is drawn from the kettle down into the piston chamber. At the top of the piston chamber there's a small (~4mm) port which leads to the group. By the force of gravity alone, a quite small amount of water flows out of the piston chamber and down to the puck. A teaspoon? I haven't measured. Anyway, it's not really enough to moisten the puck thoroughly. So I allow the lever to rise a bit, still under the guidance of my hand, maybe a third of the way up, until I see a drop on the PF spouts. That pushes some water gently into the puck. Then, I count off the preinfusion-- maybe it's a little less time if I'm pulling a single rather than a double--I've gotten to the point where I'm like the POWs in The Great Escape and time has become second-nature But here is where the single and double differ: when the preinfusion is happening, I've got my hand on the lever and it's risen about one-third of the way,where I've stopped it; if I'm pulling a single, I simply let the lever rise the rest of the way under its own power; if I'm pulling a double, I depress the lever to fetch more water and only then do I let it rise under its own power.

Does the temperature of the pre-infusion water affect the taste much?

I think temperature is all important. I've had delicious espressos when the water temperature was ideal, and pressure varied quite a lot. But I've never had a good espresso when the water was too cool or too hot. Decreasing or increasing the brew-pressure won't save a shot where the water temperature is too far from optimal.

In a Pavoni for example the water slowly soaking the puck during pre-infusion will be at a higher temperature then the pre-infusion soaking in a Peppina (or my Presso). Does this mean Gravity-levers etc would benefit from a shorter pre-infusion?

I think just the opposite: gravity levers permit a longer preinfusion because their water temperature is optimal not superheated. You would want the preinfusion not to last so long that the water temperature falls outside the optimal range.

Is pre-infusion important as a brewing step? Does the coffee extracted during pre-infusion affect the taste in the cup much?

I think yes. A uniformly swollen puck also helps in getting a more even extraction: there aren't dry channels for the water to seek out a path of least resistance.

Regards
Timo

[hbuchtel]

P.S. Did you receive your Zerowatt

The Zerowatt and Caravel are waiting in Guangzhou for me (brought from Italy by a friend), but I won't have time to pick them up till later this month

Henry

[happytamper]

Looks like a pre-infusion and the necessity of one will be different according to the type of machine. For me infusion means the forcing of water into the puck under pressure.

With the La Peppina the pressure of the pre-infusion or pre-wetting can be manually adjusted with each pull whereas with the Pavoni it will be at least .8bar. As henry stated.

So with the la pavoni we can have a pre-infusion. Whereas with the La pepinna the operater can either pre-infuse under pressure or pre-wet without pressure by guiding the handle.

Perhaps that accounts in my experience for the more full bodied espresso that comes from the Pavoni and the lighter bodied espresso that comes out of the La Peppina.

[hbuchtel]

Two after-nap espressi seem to indicate that (on the Presso at least) a short ramp up produces a much smoother and richer drink then the 'Pavoni-style' pre-infusion I was using before!

Henry

[hbuchtel]

Many who hear "flat temperature profile" likely assume that it means just that, i.e., except for the first few seconds, the coffee puck experiences the same extraction and brew temperatures throughout. In reality, the temperature from the top of the puck to the bottom doesn't converge until the last seconds of the extraction, and of course the brew pressure spans the range of 9 bar at the top of the basket to atmospheric pressure at the exit.

In a Pavoni for example the water slowly soaking the puck during pre-infusion will be at a higher temperature then the pre-infusion soaking in a Peppina (or my Presso). Does this mean Gravity-levers etc would benefit from a shorter pre-infusion?

I think just the opposite: gravity levers permit a longer preinfusion because their water temperature is optimal not superheated. You would want the preinfusion not to last so long that the water temperature falls outside the optimal range.

(quoted for reference)

Timo, Mitchell (and any other reader), here's what I'm thinking-

In a Pavoni, when you lift the lever and allow water into the chamber the water temperature is higher then optimal. For this reason alone pulling a shot right away would be bad. (this is guesswork on my part . . . )

During the pre-infusion step there are two interesting things that are going on- (note: I am ignoring the swelling effect on the puck! I do agree this is important.)

1. The group head is drawing heat from the water sitting between the piston and the puck. This is important to achieve proper brew temp. The length of time you wait would depend on the temp. of the boiler and the temp. of the group head.

and

2. Water at boiler-pressure is being forced through the puck. As it moves slowly through the puck it is also brewing the coffee. The water in question starts at a higher then optimal brewing temperature and by the time it passes through the puck is at a lower then optimal (really?) temperature.

Ok, I hope somebody is still reading at this point!

So I'm most interested in #2.

Will the coffee extracted during this step affect the final flavor much? IF YES, then-->

Comparing a Pavoni and a Peppina, the Pavoni will be extracting with higher temperature water then the Peppina and therefore can deal with a long pre-infusion without producing off-flavors..

Ugh. I'm tired of thinking.

Basically I found a Pavoni-style pre-infusion was not working on the Presso, and I've been wondering why.

Thanks to anybody who has read through this, and I'd appreciate your thoughts.

Henry

[timo888]

...Water at boiler-pressure is being forced through the puck. As it moves slowly through the puck it is also brewing the coffee. The water in question starts at a higher then optimal brewing temperature and by the time it passes through the puck is at a lower then optimal (really?) temperature.

<snip>

Will the coffee extracted during this step affect the final flavor much?

Henry,
Am I inferring correctly that you're asking whether the first few drops from preinfusion adversely affect the flavor, and if you should therefore not place your cup under the spouts until the true infusion begins, letting the first few drops fall into the drip tray?

I don't think the effect is adverse, although some do. Jim Schulman mentioned that some baristas will discard the first few drops. All I can say is that I get some very tasty cups of espresso catching every drop--though I do tend to remove the cup later in the process if the stream thins and blondes. But on the Peppina, which provides the same pressure every time, it's easier to dial things in than it is on the Cremina, and I can usually leave the cup in place till almost the very end.

On the Cremina, my only experience with a pressurized lever, I can cause the water to enter the cylinder fairly gently, or furiously, depending upon how high I raise the lever. I have dropped the pressure down quite far by adjusting the pressurestat so there's still plenty of steam for two cappas and the water showers down from the dispersion screen. I tend to lift the Cremina's lever gingerly, about half-way, to fill the piston chamber slowly. Then I gently press the lever down part of the way to force some water into the puck. Then I either pull the lever down the rest of the way for a single, or raise the lever once again to fetch more water for a double. A lungo on the Cremina goes like this chez Timo, but to each his own:

lento
Up ~halfway, wait a few seconds, and down a little for the preinfusion. Wait some more.
Up again gently for more water then down halfway.
Up again for more water and then down all the way.

I don't know if the Pavoni works this way. On the Pavoni, can one reduce the fury with which the water enters the the puck by raising the lever slowly only part of the way up? What do you see emerging from the dispersion screen when you experiment in this fashion with no PF in place? A trickle? A gentle shower? A furious rain?

Regards
Timo

[hbuchtel]

...Water at boiler-pressure is being forced through the puck. As it moves slowly through the puck it is also brewing the coffee. The water in question starts at a higher then optimal brewing temperature and by the time it passes through the puck is at a lower then optimal (really?) temperature.

<snip>

Will the coffee extracted during this step affect the final flavor much?

Henry,
Am I inferring correctly that you're asking whether the first few drops from preinfusion adversely affect the flavor, and if you should therefore not place your cup under the spouts until the true infusion begins, letting the first few drops fall into the drip tray?

Thanks for extracting that!

As the Presso is a two-hand affair I have been drinking every drop, and was assuming that too long of a low-temp. pre-infusion was adversely affecting the taste.

You're right, I had forgotten that tradition of discarding the first few drops! I guess I should find an extra hand and do a "Test of Thirds" mentioned about 2/3rds of the way down in this article that Dan Kehn wrote:

The first third of a pour is the most pungent and gives the espresso its "punch" in the same way that the higher percentage of cocoa defines the character of dark chocolate. Depending on the initial starting temperature, the first third can also tend towards sour flavors. The second third of an espresso pour is the crowd pleaser. In fact, some baristas intentionally let the first few seconds of the pour fall into the driptray to emphasize the sweet and creamy nature of the second third, but in doing so you'll potentially sacrifice the character that makes the blend interesting. The last third is weaker, lacks body and sweetness, and in some blends tends towards bitter flavors as more caffeine is extracted. Some baristas are tempted to end the pour well before the last third is complete and before the onset of blonding, but skilled professionals often let it flow longer than newcomers, knowing that the last portion can add a pleasing complexity to the shot.

Henry

[timo888]

Here is a pic of the crema that the Arrarex Caravel (open-boiler gravity-fed) can produce when the piston is pushed to pressure extremes its little o-oring can hardly tolerate:



Preinfusion: ~20 seconds. Two additional pulls of the lever, maybe 20 seconds in addition to the preinfusion.

It's hard to go wrong when the water is at the right temperature

Normally with the Caravel I go for less body and a thinner mouthfeel, and pull a sweet lungo with flavors more delicate than intense.

This is Intelligentsia's Papua New Guinea, btw, delicious, but happily not a coffee in their Get High Sell High program, and so one that I can afford

Regards
Timo
P.S. Not a drop from the spout that didn't go into the cup.
P.P.S. In the crema, do you see the silhouette of a man wearing a fedora, walking to the left, dragging a carpet bag behind him? Or Donald Duck?

[timo888]

When the Romans wished to quarry stone, they would drill holes into the stone with an auger and then hammer pegs of dry wood into them. These pegs they would then douse with water, and the hydrostatic pressure of the water being absorbed into the wood was so strong that it split the rock into slabs.

The swelling of the puck operates under the same principles and is a primary factor in the establishing the pressure profile and thus is very important to the extraction process. Illy (who alludes to the quarrying practice described above) writes as follows in ch 8.5.4 of The Chemistry of Quality:

...a chemical hydration of the organic material ... takes place. The water... is bound...in a state differing not only from the normal liquid state, but also from that of interstitial water, which is subject to laws of capillary phenomena.... During expansion, the coffee grounds exert a pressure comparable to that of the wooden wedge used to cleave marble blocks.... The actual expansion of the cake varies with blend, roasting degree and dose, and determines the exact head space (around 5-6 mm) needed to prevent over-compacting....

Regards
Timo