# Colour changing flow



## -Mac (Aug 22, 2019)

Can't find anything anywhere, maybe I'm not looking for the right key words...

Assuming a normal and 'good' shot (say 18g at the correct grind for a 27 sec shot), does the rate at which the colour of the rat's tails changes from dark to light tell us anything useful, or does it just depend on the type of bean?


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## El carajillo (Mar 16, 2013)

Before the common use of accurate scales for measuring the brew it was common to watch the tail for blonding= past best of extraction.


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## -Mac (Aug 22, 2019)

I get that, but does the speed at which it changes mean anything significant?


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## ashcroc (Oct 28, 2016)

-Mac said:


> I get that, but does the speed at which it changes mean anything significant?


It could be an indication of channelling or it could just be the bean.


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## Hasi (Dec 27, 2017)

Am I rightly assuming we're talking double spouted PF?

It's really difficult to tell with all that geometry between basket and spouts. more insights and conclusions can be drawn from watching an extraction through a bottomless PF:

If your colour change happens across the whole puck roughly at same time, it's the bean that doesn't have any more to offer at that grind setting

If your colour change happens on one side only (maybe accompanied by splutter or spritzing), there's channelling.

If you can, I'd recommend using a bottomless PF at least for training purposes! Maybe this didn't really add to answer your question, hope it'll help you anyways ?


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