Coffee Profiling 101 - Temp, Pressure & flow.

What's coffee profiling?

It's basically one's attempt to develop coffee recipes that you can repeat & apply  to get

a great espresso.

It is about achieving the perfect balance between sweetness, acidity, and bitterness.

The flavour of your coffee will depend on many factors, such as the type of coffee beans, degree of

roast freshness, temp of the group head, pressure & flow, coarseness or fineness of the grind, initial dose of ground coffee, your ratio and tamping pressure. 

It's all very complex and daunting at first. This is why I love the subject of coffee. The goal of that perfect cup is probably NEVER attainable but the path is so interesting.... a quest for the holy grail.

This post covers mostly 3 factors ... Temp, pressure & flow

Brew Temperature:

Temp profiling (the standard range is between  85 degrees - 95 deg C).

Many tasting panels have found that espresso is more bitter and astringent when it was brewed at 96 °C and 98 °C.... but you be the judge.

The hotter you go, the more you will extract.

General rule of thumb:

Light roasts - 90 - 95C

Medium roasts - 88 to 92

Dark roasts - 85C to 90C

Getting the correct temp is really difficult esp with old lever machines like the Europicola & Elektra La casa. Temp surfing is a real art. That's why people started to put PIDs on them. 

And there is the argument of flat line temp brewing vs actively changing temps during the brew.

People talk about peak temps or average temps. Most machines produce a range of temps. But what's impt is I think consistency from brew to brew.

There are many different methods to Temperature surf. You can draw water out of the group head before pulling a shot to either raise or lower the temp (depends on the machine).

How does the temp effect the taste?

Remember, The hotter you go, the more you will extract.

The ranges are just a window. They can have an effect on taste, though things like Ratio & or the initial dose can have a bigger impact.

However what's the connection between  flow rate & pressure & how does this connect with:

Flow rate profiling & Pressure profiling.

The flow rate is the volume of water that goes through the coffee grounds in a given amount of time.

pressure is the force that the water exerts on the coffee grounds throughout the extraction process. 

A unique feature of the Elektra Microcasa Leva (left) is its very large group head. It is a very effective heatsink. When water first hits the puck, its very hot, but this temp decreases quickly thanks to the group acting like a heatsink.

On the Elektra, if you get the group head to about 70c, keeping the boiler pressure at an average of 1 to 1.25 bars, then the water in the group head should be around 90-95C.

The La Pavoni Europiccola / Professional behaves very differently.

The group head has less mass, so the temp is closer to the temp of the brew water. It's probably good to add a heatsink to the group head.

On the La Pav, if you get the group head to about 80-83 c, and keep the boiler pressure at an average of 0.5-0.7 bars (I think this equates to 116C), then the water in the group head should be around 96C.

Brew Pressure:

Pressure = flow x resistance.

In our case, resistance is the puck.

The puck will degrade as you blast it with water pressure.

Thus, pressure will generally decrease as you approach the end of the brew.

Most espresso machines use a straight 9 bars of pressure.

There appears to be a peak of flow  for most espresso machines at 9 bars.

On a lever machine you can change/maintain the pressure as you brew.

Brewing can be divided into 2 stages.

Stage 1 : Pre-infusion -  this stage starts the moment water enters the basket and ends when the machine has reached it peak brewing pressure.

The aim is to get all the coffee evenly wet before the peak force pushes through the puck.

Increasing the time of pre-infusion will promote evenness of extraction leading to better tasting coffee.

Typically, pre-infusion pressure falls within the range of 0.5 to 4 bars. Espresso machines usually have 1 to 2 bars allocated for pre-infusion.

The ideal Start Time of pre-infusion is between 8 - 12 secs.

If Flow starts after 1–6 secs the espresso will usually be under extracted.

If Flow starts after 12 secs the espresso will usually be over extracted.

On a spring lever machine such as the Londinium, Faema Famenia or Elektra La Casa, 

you would pull the lever down, preinfuse (for as long as you like) then let go of the lever and 

watch it go up. They are really easy, forgiving machines.

The type of coffee will have a big impact.

Generally:

Light roasts tend to be dense so need a long pre-infusion (up to 5-8 secs) 

Medium roasts like a shorter  5 sec pre infusion 

Dark roasts can be quite bitter ... use a 2-4 sec pre infusion

Stage 2: Main brew.

In a electric pump machine the pressure is fixed ... usually 9 bars or 8 bars.

You could set it to 7 or six. ??

The higher the pressure, the finer you can grind.

The disadvantage of using higher pressures is that water looks to channels at these high pressures .

Which is bad for evenness.

At lower pressures, there is less tendency to form channels in the coffee. You can also grind coarser.

and your shot can be more balanced.

This is a reason in favour of old school lever machines.... as your shot progresses, the pressure decreases, making channeling less likely.

Flow Rate

Factors like grind size, tamp pressure, water pressure & water temperature have a significant influence on flow rate.

Coffee roast levels and age of beans also effect this.

Flow and pressure are related.

Pressure is an input to your recipe,  where Flow is an output

Flow rate is typically calculated by measuring the quantity of water that flows from an espresso machine group head over a fixed amount of time. The total weight of water is then divided by the time, giving us a figure in grams per second (g/s).

In theory, controlling the rate at which brew water passes through the coffee – or flow profiling – will enable the barista to precisely target acidity, sweetness, bitterness, and body to create a unique espresso shot.

Summary:

Light roasts tend to be dense so need long pre-infusion (up to 5-8 secs) and a slow flow 2-3 g/s.

Then increase the flow for 5-8 seconds until you achieve 5-7 g/s of coffee.

Medium roasts need a faster flow ... use a 5 sec pre infusion of 5-6g/s.

Then, increase the flow by 30% at 6.5 to 8 g/s.

Dark roasts can be quite bitter ... use a 2-4 sec pre infusion of 10g/s

Then lower the flow rate to 4 grams per second 

This is all a personal taste thing. So do what tastes good for you.

I think the important things are:

1. avoid channeling. Use a naked portafilter to check for channeling.

    drop the pressure if you see channeling.

2. Have small changes to flow ... ie small gradual changes in pressure are good.

3. Longer pre-infusion... make sure the puck is saturated.