Grinds

[faemafamily]

Hi,

Id need some theory about grinding coffee beans, being unsure how fine the grind should be. I heard that the ideal extraction time for an espresso (ristretto) should be around 25 seconds. If longer, then tamp it less or grind the beans coarser, if shorter, tamp it more strongly or make the grind finer.
Heres what I notice: sometimes, even though Im using the same grind, the result will vary, giving me overflow or overextraction. At other times, the coffee flows out beautifully but then tastes surprisingly bitter. When that happens I almost always observe grounds at the bottom of my cup.
Id like to make the most of my coffee, so what do I do wrong? Should I grind it differently on rainy days? Id appreciate your inputs.

PS: I have a machine based on a E61 group, a Mazzer Mini grinder, top quality coffee in top condition (fresh and all)

[Bullitt]

Re: Grinds

When you say "coffee flows nice", if you mean it starts out very slowly and a solid brown colour, slowly increasing to a solid flow and slowly going lighter in colour, over the approx 20-30 seconds, but not going very pale yellow, which indicates blonding and overextraction, then if it tastes bitter it may be the brew temp was too high.  This is not uncommon in HX machines that have been sitting idle for a while, and can easily be overcome by flushing some water through the the group to bring it back to normal brewing range, before actually pouring the shot/s....the water can be used to preheat the cup/s you are going to use.
Yes you will need to do some adjusting of grind size, depending on ambient temperature and humidity,... Lower humidity and/or higher ambient temperatures generally require finer grind, but high humidity(raining) and/or lower ambient temperatures generally require courser grind.
If you have some fine grinds in your cup it is possible that the burrs in your grinder are giving uneven grinding, and there are some small fines amongst the grinds.

[faemafamily]

Re: Grinds

I mean it really looks like liquid gold, amber brown, dense, etc. I always do a group flush and the machine hasnt been idle for at least a year and a half.
Thank you for your reply

[jaysonleow]

Re: Grinds

If longer, then tamp it more strongly or grind the beans coarser, if shorter, tamp it less or make the grind finer.

I think youve got it the wrong way around regarding tamping. If its longer than 30seconds, you should be tamping with less pressure, and if its less than 20, you should be tamping with more pressure.
That said however, try to vary the grind size as opposed to the tamp pressure, as it eliminates one variable.

Also, keep your dose constant each time to achieve consistent results,

Best of luck,

[rmoulynox]

Re: Grinds

I wont rehash what has just been said about temperature, but the important thing for me is only change one thing at a time, accepting that grind will need to be changed regularly. Tamp the same, dose the same, adjust grind to affect flow.

You havent mentioned what machine or grinder or tamper you are using, and this could be a big factor in the advice given here.

[jaysonleow]

Re: Grinds

You havent mentioned what machine or grinder or tamper you are using, and this could be a big factor in the advice given here.

The type of coffee, and how fresh it is could also play a major part.
Also, if its tasting surprisingly bitter, you may be letting the shot run for too long. You should try to cut the shot as soon as blonding creeps in regardless of the volume extracted.

[faemafamily]

Re: Grinds

I think youve got it the wrong way around regarding tamping. If its longer than 30seconds, you should be tamping with less pressure, and if its less than 20, you should be tamping with more pressure.
That said however, try to vary the grind size as opposed to the tamp pressure, as it eliminates one variable.
,

Thats what I meant, it was a mistake.

As I added in the original post, I have a Mazzer Mini grinder, and the beans are a very fine product from Haiti.

[Thundergod]

Re: Grinds

If longer (than 25 secs), then tamp it more strongly or grind the beans coarser, if shorter (than 25 secs), tamp it less or make the grind finer.

I think youve got it the wrong way around regarding tamping. If its longer than 30seconds, you should be tamping with less pressure, and if its less than 20, you should be tamping with more pressure.

I think they got it right (I did read it twice myself when they first posted).

Read it again with my addition which refers back to the previous sentence.

Make sense now?

[trentski]

Re: Grinds

Your beans come from Haiti? How many days since the day they were roasted are you using them?

Is it a very dark roast?

[Dimal]

Re: Grinds

Just on Tamping....

Tamping force per se doesnt really have a lot to do with the nature of the pour providing you use enough force in the first place to form a cohesive coffee puck in the basket.

Since the most oft quoted Tamping Force Standard is 30lb or as often expressed here in Oz (in rough terms), 13.5Kg, the latter will be the value used. When this force is applied via the Tamper to a correct dose of coffee in a standard 58mm Filter Basket, it equates to a surface pressure on top of the coffee puck of 0.51Kg/cm².

Compare this then, with the force being applied to the puck when 9 Bar of water pressure is applied to the surface of the coffee puck. 9 Bar is equivalent to 9.18Kg/cm² or a Total Applied Force of 242.54Kg. So when you look at it like this, the initial applied Tamping Force is barely over 5% of what is applied when you hit the Brew Switch (or equivalent).

Probably the most you would notice between a soft tamp and a handstand tamp would be the time it takes before you observe coffee starting to drip from the spout but after that, its all about the force being applied by the pump.

Just something worth noting...

Mal.

[emckissock]

Re: Grinds

Interesting theory mal, but empirical testing suggests it is not always the case.

I do find that tamping harder than normal makes very little difference to the pour rate, but that is because I tend to tamp quite hard in the first place and have a slightly coarser grind than some.
When I went on a barista training course, the first shot I tried to pull choked completely (30 sec and only a couple of drips) - the grinders had been preset and run to fil the doser.
Using a light tamp allowed me to get a good pour rate.

Im sure your calculations are accurate, but I suspect the fact the tamper is a solid object and water is able to percolate through the grounds has some bearing.

[Dimal]

Re: Grinds

Not a theory mate, totally factual..... 8-)

Mal.

[Dimal]

Re: Grinds

Tamping force per se doesnt really have a lot to do with the nature of the pour providing you use enough force in the first place to form a cohesive coffee puck in the basket.

Not a theory mate, totally factual..... 8-)

You didnt take into account the first paragraph, especially the highlighted section.

Mal.

[emckissock]

Re: Grinds

A light tamp that forms what I consider a cohesive puck - 30ml in 30sec with the preground coffee provided to me (tamp somewhere around 10-12kg from memory)
A heavy tamp that also forms a cohesive puck approx 1 ml in 30sec.
Only saying what I experienced in a real world situation.

I do agree that there comes a point where additional tamping force has marginal effect, which is something below my normal tamping force. Just for grins, I measured it on the bathroom scales, I normally tamp around 15-16kg. This would suggest the point at which increased tamp force has relatively little impact is between the 12kg and 15kg force.

Im still convinced that the application of force by a fluid on a mass of particles is fundamentally different to that of a flat stainless tamper, but fluid dynamics was never one of my strengths so explaining the details is beyond me.

[galumay]

Re: Grinds

Yep, no doubt tamp pressure has a very real and obvious impact on the pour. Its simple enough to demonstrate, use the same amount of coffee, with the same grind settings and time the pours. The more pressure with the tamp the longer the pour.

Ultimately its not what pressure you tamp at that is so important as the consistency of your tamp. I used to tamp at around 30lbs and overdose, now I dose at around 14g and tamp at about 15lbs as I prefer the flavours I am getting.