Hot grinders

[James Hoffmann]

I am probably going to come across a bit stoopid here but what the heck.

I was working on a machine today and the grinder was a 700 rpm flat burr grinder. We put about 8 kilos through in around ten hours. No surprises - it got hot. Very very very hot.

Now I would expect heat to cause metal to expand, causing a decrease in the gap between the burrs causing me to shift the grind coarser but the opposite of this happens, the hotter it gets the finer you have to grind. This has happened on several occaisons.

So what I want to know is why. What is the heat destroying, or affecting that is linked to flow speed?

[Deferio]

Hey Kingseven,
I always held that the heat of the grinder destroys the flavor oils in the bean...not all of them but some.
This to me suggests that the grinder would not be putting out a different partical size...but a partical of coffee with less oil.
It would then make sense that you had to adjust the grind finer....
reason being that espresso when packed together creates a seal that offers resistence to the brew water coming down. The seal is formed from the exposed and sticky oils being compacted...(much
like partical board is saw dust and glue compressed)
So it follows that if there is less oil then you have a weaker seal and therfore a faster extraction time.
Hope that helps some.
-Chris Deferio

[James Hoffmann]

The oil thing was the first thing I thought - but then most oils are stable at relatively high temperatures (certainly the temperatures likely to be reached between the burrs).


The amount that I am having to shift the grind indicates something else. 3 clicks on a Lusso in 6 hours...

[Jimmy Oneschuk]

The heat from the warm burrs reduces the ability to actually grind finer, thus the overcompensation. Similiar thing when cutting fresh pasta... when the metal dies get warm, your pasta starts to stretch instead of breaking cleanly.

Hopefully AndyC will weigh in and school us all!

[nick]

Not just oils, but water.

When the grounds come out hot, they expel moisture that was in the bean. Drier grounds means a faster extraction. So you have to go finer to compensate.

At least that's what I always thought.

[Jimmy Oneschuk]

What sort of sensory and technical characteristics do you smokin' hot grinder users notice in your espresso? crema decrease? distinct loss in flavour resolution (I'm making up words here )

[Pe_tah]

Daym... so thats why I had to adjust my grind when it got really busy....I was seriously like "Dude, who adjusted the grinder???" Good to know...

[nick]

What sort of sensory and technical characteristics do you smokin' hot grinder users notice in your espresso? crema decrease? distinct loss in flavour resolution (I'm making up words here )

In my experience, the espresso just tends to be flat. Resembles an underextraction, but not exactly so.

I guess the closest thing is it's like having dull burrs.

[PureArabica]

Dull burrs is closest thing I can compare it too.
Loss of crema, loss of flavor complexity, taste kind of burned.(I have a mazzer S/J and a rossi r45)
Nick