How much are you dosing into the basket?

 

So everything is consistent but the shot time varies. You are:

• 
  weighing the ground coffee you put in the portafilter and keeping it the same (coffee weight in grams) for each shot
  
• 
  Or the grinder has been set up to dose a consistent weight and you don't let the hopper get too empty
  
• 
  Using a good quality grinder and the grinder burrs are not worn out
  
• 
  Purging if there's been a wait longer than 20 minutes or so
  
• 
  Aiming for the same target extraction weight in grams for each shot
  
• 
  Using fresh coffee that's been properly stored
  

I would expect a few seconds variation down to prep and tamp pressure but nothing like you are experiencing...what grinder are you using?

P.S. The use of pre-ground coffee is a real red flag and a very poor practise.

 

There just isn't time to weigh the coffee when there is a queue of customers waiting - but I know just from sight that I sometimes have to use significantly different amounts of coffee for a similar result depending on the time of day. What is roughly 17g (as recommended by the bean supplier) works at one point in time, not another.

The grinder is pretty terrible and I'd love to replace it but the fact that the extraction time changes even for pre-ground coffee - done by the coffee supplier for espresso machines - suggests it's not a fault of the grinder here? (Here's a photo of the grinder though, and the amount of mess we end with!)

Purging - good point, I suspect we are a bit hit and miss at doing this. Could that on its own be causing the huge variation?

PS Yes, agree to the bad use of pre-ground coffee. It's for decaf. We don't have a second grinder for it (nor the space) so we buy it pre-ground in 250g bags.

 

There just isn't time to weigh the coffee when there is a queue of customers waiting

Good coffee shops seem to manage it. At least a few times to make sure the OD grinder is dispensing accurately through the day.

It only takes a couple of seconds. Probably quicker than redoing a shot and less wasteful.

As Dave says you'll need to adjust the grinder through the day.

The fact this happens with the pre-ground does indeed suggest something is going on though. Inconsistent dosing, poor distribution, poor tamping (given you don't have time to weigh the grinds I'm guessing you don't have time to get these right either). When you say "I can fill the portafilter right up" are you ramming the puck against the shower screen?

Are all of the groups set to the same temperature and pressure? Do you see this inconsistency across all groups?

 

Well I think we identified all the little problems that contribute to the large variations

Fix those and realise the grinder may need to be adjusted throughout the day.

 

Thanks all.

Weighing - I did sit in an excellent coffee shop watching them weigh the coffee, but they fortunately had a slow but steady stream of customers. I had a backlog of 18 drinks to make on Saturday and when customers are asking where their drinks are, it's difficult to spend more time weighing things out - especially when there's no guarantee that the correct weight will actually work anyway. But good point re. time taken to make a new coffee.

Grinder adjustment - I am always so wary of adjusting it because it can only go finer if free from beans, and it is so much trial and error to get right which of course is not what you need when a customer walks in. Maybe it just needs more practice to get a sense of what's right.

As bad as the grinder probably is, the inconsistency with pre-ground coffee does seem to point to a different root cause though.

@Rob1 I mean I can put as much ground coffee in as is physically possible - around 22g - and I have no idea if it's going to come out quickly or slowly.

@Rob1 Temperature and pressure of each group head is, I believe, the same - I'm not sure how to tell with this inheritied machine. All I know is that they generally behave or misbehave at the same time, (and no. 3 dispenses water for about 2s longer than the other two)

Customer behaviour is unprectable at the moment but if last week is anything to go by, this Thursday will be dead quiet. We will weigh the coffee then so that variable can be ruled out (or not).

 

Weighing - I did sit in an excellent coffee shop watching them weigh the coffee, but they fortunately had a slow but steady stream of customers. I had a backlog of 18 drinks to make on Saturday and when customers are asking where their drinks are, it's difficult to spend more time weighing things out - especially when there's no guarantee that the correct weight will actually work anyway. But good point re. time taken to make a new coffee.

I think you may be overestimating how much time it takes. Get yourself a pair of scales like the ohaus navigator xt which will pre-tare to the weight of the portafilter, then when you grind your coffee into the portafilter simply drop it onto the weighing plate for a second. You at least need to do this to debug, as if you're using inconsistent doses you need to eliminate that variable.

Grinder adjustment - I am always so wary of adjusting it because it can only go finer if free from beans, and it is so much trial and error to get right which of course is not what you need when a customer walks in. Maybe it just needs more practice to get a sense of what's right.

Also about having a routine. Are you dialling in at the start of the day, for example? Adjust the grinder while it's running, and remember to purge a few grams between adjustments.

I think there's a lot to be read between the lines from your comments about the machine, grinder and your experience. You need to take some time on a day you're closed or before/after opening to figure out exactly how to best use the equipment you have.

I'm unbourdoned by the costs of running your business which allows me to freely say that in an ideal world you'd be able to partner with a local roastery who will normally be more than happy to send someone over and help you get the best out of their coffee using your equipment. You'd get better coffee as a result and support that part of your local economy. I appreciate that this isn't always going to be possible....but something I'd seriously think about.

I'd be interested to see a video of you preparing and pulling a shot, see what we can learn from that.

 

heat, humidity and atmospheric pressure massivly impact the coffee grind, if theres a thunderstorm you will need to change your grind settings for example. One reason why preground is really never recomended. Static and heat change the volume of the coffee in the portafilter too, which is why everyone is suggesting weighing, You don't need to weigh evey shot, but it will help consistancy to know roughly how it might change through the day. but at the end of the day, it is always a moving target as you have little chance to control all the other variables.

If your getting 5 second shots, randomly, thats more than likely channeling, and thats down to distribution issues like uneven tamping.

 

What's good about all of your replies is that is sounds like the problem is not with the coffee machine itself, which is good as that's the most expensive thing!

The bean supplier does do training and that was going to be arranged in April until coronavirus happened. Hopefully it can be rearranged soon. Some local guy does the maintenance.

@catpuccino Thanks for scales suggestion, that sounds faster to use than the ones we have at the moment.

I will try all your suggestions over the week and see how I get on (and try to do a video @catpuccino, great idea)