If you are trying a bottomless portafilter for the first time, and it pours coffee out everywhere, and you don’t obtain the beautiful coffee flow that you expect, it may not sound like it, but this is good news.
The design of the bottomless portafilter is simple, meaning there are only two places where unwanted coffee leaks can occur:
1. between the rim of the basket and the rubber seal in your machine (may be dribbles of hot water or squirts).
2. squirts of coffee in all directions from the small holes in the basket.
If the leak is between the rim of the basket and the rubber seal in your machine, then it is time for a new seal in your machine. These become hard over time and require replacement every 6 -12 months. Of course check the top rim of the basket to make sure it is smooth and undamaged and the gasket area in the machine is cleaned regularly with a stiff brush to remove accumulations of coffee debris.
If the coffee is squirting out in all directions from the holes in the basket, the the problem is down to the coffee used or technique (or both).
The bottomless portafilter is designed to let you see if there are any problems with your shot. These problems are normally covered up with a standard portafilter – all you can see is what emerges from the spout.
Thankfully we have come across this a few times and there are a few easy steps to a solution.
The problem is often down to the coffee grind/freshness and the tamping.
You will need a freshly ground bean. If you do not have your own grinder, I would recommend getting an espresso grind coffee from a local delicatessen, or from Whittards. The beans should be fresh (roasted withing the last week or so), and once ground they should also be used within a week or so. Any longer and they will dry out and loose all their oils and flavours.
Your coffee pack should have a “Roasted On” date, and ideally you should use it between 1 week and 1 month from that date for optimum taste. If it has a “Use By” date it could have been roasted anything up to 6 months ago. The ground coffee in this case will be dry (devoid of oils) and will be very likely the cause of all your problems. You won’t get good crema, as few coffee oils remain, and the dry powder results in channeling and coffee spraying out of the basket. Don’t use Lavazza or other pre-ground as you will be spoiling your chance of a incredible cup of coffee.
The next thing is the tamping. With the coffee machine good and hot (ideally 30 minutes of warming time with the portafilter in place), fill the portafilter basket, and using a flat based 57mm tamper (for our Gaggia bottomless portafilters), tamp the grinds down with a reasonable force (30 pounds or 15kg of force). You can practice this on the bathroom scales.
With fresh coffee, and a good tamp, the puck of coffee in the filter basket should stay in place if the portafilter is turned upside down. Too old (ie dried out) and the grinds will not stick together as all the oils have been lost due to evaporation, or insufficiently tamped meaning the grinds are not pressed tightly together forming a uniform layer for the hot water to pass though. This will lead to cracks forming under the pressure of the water passing through and small jets of water spraying out to the side of the basket.
Insert the portafilter in the coffee machine and run the hot water through the for 20 seconds or so, and you should have a perfect shot. If you look at the underside of the portafilter when you start the shot, the dark coffee should emerge slowly after a few seconds. This will form one or two trickles (described as mouses’ tails). Continue to let the coffee flow until you can see the dark brown coffee lighten, with just small streaks of dark coffee running through. At this point (the “blonding” stage) you should consider stopping the shot.
Of course, you can improve on the steps above, but this is just to get you used to something close to a good extraction.
Here is a short video of a customer with coffee spitting everywhere. This is due to dry old coffee and under-tamping.
This is the result he should have got (okay I did under-tamp it and so the coffee flow was a bit too fast, but it is difficult to tamp holding the camera, and hopefully you get the idea):
The main problem the buyer had was using a rotary grinder which gave variable grind size, the coffee was rather dry, and the tamping was insufficient.
You might also like to view the following links which go into further detail: