How to tell if coffee beans are over roasted
Coffee is all down to preference.
Some like it hot, some like it cold.
Some people take it with milk and sugar others prefer it long and black.
There are folks that enjoy the complexities and subtle floral notes in light roasted coffee whereas the opposite end of the flavour spectrum, dark, roasty notes are enjoyed by many.
This all being said, if you are a lover of dark roasted coffee then you may be living on the edge of over roasted coffee. But how can you tell and when do you know that coffee is over roasted?
It is however down to personal opinion of course, whether a coffee is over roasted, however we’ll guide you through some tell tale signs.
Why Trust Me?
How do you know if coffee is over roasted?
So there are a few key signs highlighted below to look out for when you’re trying to figure out whether your coffee beans are over roasted.
The Look of Over Roasted Coffee
Identifying burnt coffee beans can be as easy as just opening your bag of coffee and taking a look at what’s inside.
Coffee beans range in colour depending on the roast.
From light roast coffee which is light brown in colour through to dark roast coffee which is dark brown.
Over roasted coffee is beyond the dark roast level and appears almost black.
Aside from the colour of your coffee beans being a dead giveaway that the coffee is over roasted there are another couple of signs that you can look out for.
If your coffee beans have an oily or shiny appearance, then there is a good chance that the coffee is over roasted.
When the coffee is roasted to this point the complex compounds are broken and the oils which add to the balance and depth of flavour in the coffee are forced out of the coffee bean onto the surface which will lead to an unbalanced cup when brewed.
The smell of over roasted coffee
Signs of over roasted coffee are also apparent in the smell and aroma of the coffee beans.
The best test is to open your bag and breathe in the aroma of the coffee beans. If you pick up a charred or burnt sensation, then there is a good chance the coffee is over roasted.
This can, however be an unfair test as there are particular types of coffee beans that can have flavour notes which are similar to smokey aromas.
For example a Monsooned Malibar coffee from India typically has tobacco and roasty notes due to the unique style of roasting.
If the coffee smells burnt alongside the coffee looking black I could then make the judgement that the coffee is over roasted.
The brewing of over roasted coffee
Over roasted coffee characteristics are also present when you brew your coffee.
If you happen to have missed the smell and appearance test and you’re now brewing you coffee wondering whether the coffee is optimally roasted then here are some pointers.
When coffee that is over roasted is brewed the extraction time is typically shorter, this is because the ground coffee is more soluble and dissolves quicker in the in the brew water leading to a bitter brew.
Depending on the brew method (anything through paper this doesn’t typically happen) you may end up with an oily layer on the surface of your coffee as the oils had already separated pre-brew.
The taste of over roasted coffee.
The taste of your coffee is another way of recognising over roasted beans.
It is hard to say how coffee should taste as there are huge swings in flavour profile when you factor in processing method, coffee type, roast type and brew method.
However, I think we can all agree (especially if you are reading this) that coffee should taste balanced and flavoursome.
If the coffee tastes unbalanced, bitter and burnt tasting then there is a good chance that the coffee beans are over roasted.
The flavour profile of over roasted coffee is usually simple as all of the complexities and sweetness have diminished, you’ll just be able to pick up a one or two bitter notes followed by an ashy aftertaste.
Is there any acidity in the coffee?
Acidity in coffee is a good thing. As long as the acidity is balanced then this element adds to the overall complexity of the coffee beans.
If your the coffee has a real muted acidity and you’re just getting the burnt coffee taste, then there may be a chance the coffee beans are over roasted.
This again, is not always the case because some types of coffee have naturally less acidity. However, low acidity in your coffee coupled with one or more of the points above may be a sign of over roasting.
The sound of over roasted coffee
This is a factor that only appeals to the coffee roasters (both professional and hobbyist). The sound of the coffee beans inside the drum (or cylinder or pan for that matter) can reflect the coffee roast level.
Raw coffee beans are essentially heated at a really high temperature for a specific amount of time with other variables such as drum speed or airflow added in.
These are a couple of coffee roasting signs that we can listen out for.
When the raw coffee beans reach two distinct temperatures (roughly 200C and 220C) the coffee makes a cracking sound (think of popcorn).
These are called first crack and second crack and the complex compounds inside the bean are changing, suddenly altering the structure of the coffee bean which produced a cracking sound.
Although many roasters roast beyond second crack, the majority of specialty coffee roasters agree that anything beyond second crack is over roasted.
Dark roast vs Over roast
It is sometimes hard to spot the difference between a dark roasted and an over roasted coffee. However if you follow the signs above here are what to look out for:
How does the coffee look? Dark roasted coffee should still be brown (although dark brown) with no oily or shiny surface.
How does the coffee smell? Dark roasted coffee may smell smokey at times but still have a sweet and balanced aroma.
How does the coffee taste? Dark roasted coffee can have a bitterness but it should also have a flavour profile and depth in its body.
Over roasted vs under roasted coffee
Opposite ends of the roasting profile. There are huge differences across the board when it comes to over roasted or under roasted.
Both are not ideal and will certainly brew low quality coffee. Under roasted coffee will be light in colour and have a subtle vegetal or straw-like aroma, the taste will be sour and flat with very little depth.
Final Thoughts
There is not much you can do when you realise that the coffee is over roasted. Although it doesn’t necessarily make the coffee undrinkable depending on how over roasted it is. I would recommend adding flavours or milk to over roasted coffee to try and mask the taste. If that doesn’t work your house plants may enjoy the flavour.
Common Misconceptions About Dark Coffee
Many coffee drinkers confuse coffee too dark with a proper dark roast. While dark roasts are perfectly acceptable and even desirable for certain brewing methods, there's a clear line between intentionally dark-roasted beans and burnt coffee beans.
A quality dark roast should still maintain its brown colour spectrum - think dark chocolate rather than charcoal. If your beans look almost black and have an oily sheen, it's likely they've crossed from dark roast into over-roasted territory.
The key is understanding that darkness doesn't necessarily equal richness - many coffee lovers mistakenly believe that darker always means stronger or more flavourful, when in fact, over-roasting can actually diminish the coffee's natural flavour compounds.
FAQs
What does over roasted coffee look like?
Over roasted coffee is dark, almost black in appearance with a shiny oily layer.
How does over roasted coffee taste compared to properly roasted coffee?
Over roasted coffee tastes bitter, burnt and unbalanced compared to coffee that has been optimally roasted which can have many different flavour profiles but will taste balanced and complex with flavours such as florals, fruity, nutty or sweet.
What causes coffee to be over roasted?
Coffee is typically over roasted to mask the poor quality raw coffee and create a consistent flavour profile which usually consists of charred and burnt notes.
Can over roasted coffee beans be harmful to consume?
There is the obvious link of carcinogens with anything burnt. However, if you are consuming a small amount of burnt coffee irregularly then it shouldn’t be harmful to consume.
Can you roast already roasted coffee beans?
The simple answer is no - trying to re-roast coffee beans that have already been roasted will only damage them further. Once coffee beans have gone through the roasting process, their internal structure has already undergone significant chemical changes.
Any attempt to roast them again will just burn the beans and create an unpleasant, acrid taste.
How to tell if coffee is burnt?
Look for extremely dark, almost black beans with a very oily surface, and an aroma that's more reminiscent of charcoal than coffee.
When brewed, burnt coffee will taste noticeably bitter and lack any of the subtle flavour notes that make coffee enjoyable.
Does over roasting coffee reduce its caffeine content?
Caffeine content in a coffee bean does not change when it is roasted (although there have been studied claiming that there is less caffeine in lighter roasted coffee, but the difference is nominal).
Having said this, over roasted coffee will loose a lot of mass and weigh much less than it’s light roasted sister. If you then grind your coffee and prepare a brew you will essentially use more over roasted coffee beans than regular coffee beans making the caffeine content higher.
Is there a way to salvage over roasted coffee beans?
Other than using the coffee beans as plant food or another use of coffee grounds, there is not a great deal you can do to salvage over roasted coffee beans. You may still be able to brew something half tasty though if you add a few extras into the cup such as syrups, milk or Baileys.