Undercooked or Underdeveloped

In this segment, I will go through my experiences of underdeveloped coffee. For those of you who do not know what this means. In short, its coffee that still hasn’t fully cooked all the way through or is unevenly roasted leaving behind traces of “green”. This can occur in so many ways and I am sure I am yet to experience every way you can end up with underdeveloped coffee. Almost every roaster will be guilty of it at some stage. I have on the odd occasion tasted underdeveloped coffee from some big name roasters here in NZ also, so it doesn't mean you'll ever be immune to it. 

What does underdeveloped coffee taste like?

Here is a list of some everyday food items you will be familiar with and can relate to

  • Green Beans
  • Green Peas
  • Sprouts/ Alfalfa
  • Cres
  • Sesame Seeds
  • Boiled Potato

There are many more ways to describe underdeveloped flavours in coffee but once you’ve experienced it (tasted it) you will remember this flavour forever. Trust me it's terrible and giving the lightly roasted coffee scene a bad wrap in the publics eyes. I have talked to people who really do not like light roasted coffee because they feel it tastes “grainy”. Its that one bad experience of an underdeveloped coffee and they are put off for life. Thankfully I have worked out the main ways I believe you can end up in this mess. But please remember that there are other ways possible not covered here.


Too little energy applied to the bean from the beginning can hugely impact the inner bean development. I think it is key to apply as much heat energy at the beginning of the roast from green to yellow transition without causing roast defects like scorching and tipping. How you apply this energy isn’t that straight forward. What charge temperature will you start with? When should you back off the gas? These are also two major factors when trying to set up a successful roast. Charge too high and the roast will end too quickly and possibly be underdeveloped, roast too slow and you end up underdeveloped. Airflow will impact also how the energy you are delivering is applied to the bean. Too higher airflow and you will strip the roaster of thermal energy and struggle at the end of the roast and potentially impart roast defects from too much convective heat early on. Too lower airflow and you will potentially underdevelop the coffee again by not penetrating the core of the coffee and also struggle to remove the chaff from the drum.


The most common ways I ended up with underdeveloped coffee in terms of energy were

  1. Too little heat at the beginning of roast
  2. Dialling back the gas too early in the middle phase (Yellow to the first crack)
  3. Going into the first crack with too little energy ( a slow start to the first crack )
  4. Pulling energy off too quickly during first crack resulting in ROR dipping down suddenly




My interpretation of a light roasted coffee is something ideal for filter or hybrid espresso (Put through a EK43). So dropped during the first crack and maybe just after. If the first crack occurred at 200 Degrees Celsius a light roast for me would be between 206c to 213c

Like I referred to in my last blog about loading a clothes washer you want to find the balance of how much coffee you should load into your machine so it has plenty of time to experience convective heat. I always struggled to get well developed lightly roasted coffee ( dropped during the first crack ) with charge close to the specified manufacture capacity. I found charging at maximum 60% or less ideally of what the drum can usually handle. For example, 3kg in a 10kg Toper, 4kg in a 12 kg Probat and 700g in a 2kg Mill City. As soon as I used this approach 90% of troubles had gone. Gone were those grainy light roasts. Sure it wasn’t easy at first controlling those small batch sizes in a big roaster but using thin fast thermocouples gave me great insight into how the roast was progressing in the later stages. I know there are roasters out there that can roast light coffee close to the drum specs but every machine is different and I found out what worked in my situations.


My interpretation of a medium roasted coffee is something ideal for espresso. So dropped not long after the first crack and maybe a little further depending. If the first crack occurred at 200 Degrees Celsius a medium roast for me would be between 215c to 220c

I felt always comfortable roasting around 70-90% capacity when roasting to this degree. The coffee drops at a higher temperature and the total roast time typically is longer 11-13 mins meaning the coffee has a better chance of being evenly roasted. Not always true I must admit but worked most of the time for me.


My interpretation of a dark roasted coffee is a coffee that has mostly roast flavour imparted on it ideal for your Italian grandad who wants a “strong coffee” and lost his taste buds in his sixties. So dropped well after the first crack and maybe entering the second crack and further depending. If the first crack occurred at 200 Degrees Celsius a dark roast for me would be between 220c to 230c

So your thinking to yourself oh shit my medium roast is tasting grassy I should go dark that’ll fix it! Ahhh no don’t even think about it, if you have underdeveloped medium roast you’ve fucked up somewhere and going darker is just going mask that shit you’ve done at the beginning of the roast and worst case you get underdeveloped dark coffee. It tastes like shit I’ve been there it's not pretty, bitter and sour in one cup... ewww. Game over don’t be here nobody will be your friend. This coffee is not for consumption but better in your compost or make a super hipster body scrub. 


Using a slow thick probe is not ideal at least in the last 2-3mins of a roast. When using a slow probe your roasts may have changed dramatically towards the end but since the probe is still catching up you don't see it happen or too late and the roast is over.  I found this out the hard way roast looked like they still had a positive ROR “Rate of Rise” but in reality, it was actually stalling. ( Stalling: The roast temperature is going in reverse /losing temperature ) . such a simple cost-effective fix to change to a thinner probe. $20 at max! If you are unsure what rate of rise is, click on this link:


Extremely dense coffee with a tight cell structure is the unexperienced roasters worst nightmare. So if you are just starting out it may pay to try roast something a little easier in the beginning.

Rwanda/Burundi: I have had a love/hate relationship with Rwandan coffee.

Love - Some high-grade red bourbons from Rwanda and Burundi are hands down in the top list of my most memorable and enjoyable coffee’s.

Hate - These little buggers are so easy to roast wrong and get disappointing results. The extremely dense nature of these coffees means they need that little bit more convincing when applying energy to them. It made me reconsider my roasting strategy to be able to evenly roast this coffee to a light degree and gain awesome tasting coffee. I lost sleep over these coffee’s and it hurt my wallet.

Extremely dense to Low dense you must roast them differently and find a way to penetrate the core of the bean as efficiently as possible. Reducing my charge size solved most of my issues. The beans were then exposed to higher amounts of convective energy. The other things that caught me were smaller but were to do with development percentages “DTR” and final drop temperature. This something you will discover on your own roaster with experience.


I hardly ever had an issue with underdeveloped coffee with the following origins

  • Ethiopia
  • Colombia ( high dense coffee from here are still troublesome at times )
  • Brazil
  • Costa Rica
  • Peru
  • PNG

There will be more but I haven't roasted them.

Choosing a coffee that has some leeway while you are learning will also be a good purchasing strategy. Ending up with underdeveloped coffee while you are learning can be extremely stressful and upsetting so please choose wisely. At times I felt like I wanted to give up on certain coffee’s but eventually go there with persistence.



Roast too fast the coffee will not have enough time to absorb the energy evenly and leave you with unevenly roasted coffee with an undercooked centre. I have learnt over the years that roasted coffee does have a roast colour gradient from the exterior to the centre. The faster you roast the larger this gradient will be and potentially so large the centre was unable to cook. For example, you are frying some delicious chicken in your deep fryer. Yes, I am hungry… The oil is way too hot and the exterior of the chicken becomes overcooked and centre is still raw when you take it out. Now you might give yourself salmonella in the process but this is similar to roasted coffee roasted too quickly.


Roast too slow and the bean may end up undercooked as the centre never felt enough heat energy and couldn’t travel to the centre. Just as bad you can also roast the coffee so slow it is fully cooked but you have baked the coffee in the process. (BAKED COFFEE = Flat, Dull and Dry ) meaning you have destroyed all that was good about that coffee. Its similar to frying chicken in a fryer set at a low temperature and setting a long cook time. The chicken is cooked yea sure! But its tasteless dull and dry with a nasty texture.



This subjective is hot debate amongst roasters and will be a little controversial. My Approach to finding the correct roast duration is by considering the following...

  1. What am I roasting for Espresso or Filter?
  2. What charge size am I working with?
  3. How dense is the coffee?

This all comes down to experimentation and seeing what direction the coffee wants to go. For a filter, I will start out with fast/ish roast around the 11min mark. I know you can roast great filter coffee at roasts times longer than this but in my experience, it wasn’t ideal.  Slowly reducing the roast times until I start to have issues with underdeveloped coffee. At this point, I now know where I can not go. I found with fast roast times for filter coffee I was able to obtain superior flavour clarity and less roast imparted flavours. Remember not too fast!



Doing your best to make sure your BT(bean temperture) curve through the whole roast has a nice declining rate from start to finish without a hard crash at the end is key to gaining well-developed coffee. If you want to know all the details about this read Scott Rao’s “Coffee Roasting Companion” I won’t go into detail here… leave it to the master.