3 reasons your coffee tastes bitter


There is nothing worse than expecting your cup of coffee to be a burst of good flavours only to end up with a mouthful of bitterness.

Bitterness is usually seen as a negative within coffee but a low level of bitterness actually helps tame coffee acidity.  Coffee is known to have some bitterness due to its caffeine content but only about 10-15% of bitterness is due to the caffeine. Overpowering bitterness or unbalanced coffee of any kind is going to be disappointing. So why is your coffee bitter? The bitter taste left in your month is often a result of one or maybe even a combination of these three things:

Over extraction

This is when too much water has past though your coffee grounds. Coffee brewing is an extraction, the amount and the evenness of the extraction is what determines if the coffee tastes good or bad.

Brew ratio is all about getting the balance between the amount of ground coffee and the amount of water used correct. Not enough water will result in a sour under extracted coffee, while too much water will result in a bitter over extracted coffee. Espresso ratio is usually 1:2.

Checking the volumetrics on your machine are delivering the correct amount of water for the dose you are using should be part of your daily set up or you could weigh the yield as the shot pours to ensure consistency. Ensuring you are weighing your dose is also a crucial step in maintain your brew ratio.

Grind Size

Just as brew ratio affects the extraction, the grind size also plays a huge part in the overall taste of the coffee.

Using a grind setting that is too fine (or even worse using a poor quality grinder such as a blade grinder or a grinder with blunt blades) would significantly alter the evenness of the extraction.

Pouring espresso too fast results in under extraction: the slower the shot pours the more strength and extraction the shot has but only up to a point. If the shot pours too slowly due to the grind being too fine, it will taste bitter.

Espresso should pour between 25 – 35 seconds, but the best results are usually found between 27 – 33 seconds.

Clean Coffee Machine - Leaf Bean Machine

Dirty machine and equipment

This is a no brainer. As you use the machine coffee oils build up and if they are not removed they will go rancid.



Many times metallic, bitter or astringent flavors in the coffee are blamed on the barista or the coffee bean when they are actually caused by dirty equipment.

It is a common belief that a machine with low usage does not need to be cleaned with the same frequency or care that a high volume machine does but this is simply not true. The increased idling time of an inactive machine with no water passing though the group head and portafilter, leads to oils build up on these parts.

Spot the difference: CLEAN vs DIRTY. A clean coffee machine is important to ensure delicious tasting coffee.

Net showers and group head assembly blocked with coffee gum will restrict the water flow and can lead to channeling and uneven extraction. Not only will this cause bitter tasting coffee but this will put stress on parts of the machine (like the solenoid and the pump) causing unnecessary wear and tear.

It is recommended that you backflush your machine with water as often as possible throughout the day and at the end of service, backflushing each group head with specialised coffee machine cleaner.

Dirty portafilters and baskets can also make coffee taste ashy and bitter if not cleaned properly. Regularly clean these parts during service and give them a good soak in hot soapy water at the end of the day, before rinsing and putting back into the machine.

And let’s not forget our grinder: doser grinders need to be thoroughly cleaned of any excess grinds and beans need to be returned to their airtight bag overnight.

If after all this you are still finding your coffee is bitter there are some other things to consider:

  • Make sure the coffee you are using is fresh, 1-2 weeks after roasting is recommended.
  • You may want to try a lighter roasted coffee.
  • Check the water is of good quality (water filters should be changed regularly) and ensure that the temperature is not too high, should be about 92 – 96 degrees.

If you would like more information regarding any of the above issues, our barista training covers detailed coffee preparation and using espresso recipe so that every coffee you make is sweet and balanced. Book online or contact us training@leafbeanmachine.com.au

– Summah (Barista Trainer)