Under extracted coffee is sour, over extracted coffee is bitter, in the middle is the sweet spot.
It is easy to over extract a dark roast, it is also easy to under extract a light roast. By measuring the density to determine the Roast Level, you get the correct level of extraction required for every roast level. Now you can find the sweet spot first time, instead of using up most of your bag of beans blindly trying to figure out the right formula.
What is SSDI?
SSDI stands for Sweet Spot Density Indicator. A catchy coffee acronym like WDT and RDT.
SSDI is a VARIABLE coffee recipe system, where each of the 10 extraction parameters are set relative to the 150 point range of measured roasted bean density. You measure the density, then enter it into the density.coffee website. The website does all the calculations for you, providing appropriate espresso and filter recipes along with an aging table to tell you how to handle your coffee.
Compared to a traditional FIXED coffee recipe e.g. (20g in, 40g out, 1:2 ratio, 93c, 25 sec) where the only parameter that gets changed is the grind size. FIXED recipes assume everything is roasted to 2 levels, either espresso or filter. Which apart from being demonstrably not true, also limits what you can use espresso method for.
With a fixed recipe, because grind size is your only tool, you must make quite large changes. Often it takes a lot of trial and error to dial in a new coffee. Many people may never actually experience the sweet spot, and simply get used to quite bitter coffee.
Think of the espresso recipe with all its parameters, as a combination lock with 10 wheels. With a FIXED recipe 9 of them are most likely in the wrong place, and you are turning one wheel (grind) in the hope of unlocking it. Much of the time its just not going to work.
With SSDI, each of the parameters vary relative to the 150-point density measurement. This achieves the right level of extraction for any given coffees roast level. SSDI results in much less dramatic changes in grind size, and much less dialling in, and greater ability to cope with a wider range of roast levels. You would be amazed how often you nail a new coffee first time.
Thinking of the espresso recipe as that combination lock with its 10 wheels. Using the SSDI method puts 9 of the wheels in the correct place, and you are making a minor grind adjustment to the last wheel. It just much easier to crack that combination and achieve the Sweet Spot.
Up until now there really has not been a good tool to measure roast level, so Roast Level has been ignored as something that needs to be factored in. But now there is a cheap tool and good method of measuring it. If you want to be able to reliably handle an endless variety of different coffees, a measuring cylinder is a low-cost thing to try with a great return on investment.
[Note these are paid links, as an Amazon Associate I earn from qualifying purchases, which may help cover site costs]
If you only ever use your one favourite blend that never changes, maybe you don’t need SSDI so much. But even then, todays mid roast is a lot lighter than back when that standard fixed recipe was invented, you too could also benefit from some tweaks.
What is the Sweet Spot?
When we look at the total mass of a coffee bean, only 30% of it consists of solubles. The other 70% of the bean is made of insoluble fibres and carbohydrates that create the beans’ structure.
About 20% of the bean contains good solubles and the other 10% are bad and taste awful. To brew the best cup of coffee we must try and release the good solubles while leaving the bad ones locked up in the cells.
Luckily the bad solubles are larger and take longer to dissolve than the good solubles so we can vary the extraction parameters to try and hit the sweet spot.
Maximising your extraction yield is not something you should do, you will simply end up with bitter coffee.
The optimal guidelines set by the SCAA for extraction are 18 – 22%. So, this means that when we take the total weight of our coffee beans, 18-22% of that mass will be dissolved by water and end up in our cup.
However, the problem is, how easy, or how difficult it is, to extract just the right amount, changes completely with the Roast Level.
What are the Roast Levels?
Coffee beans have some of the strongest cell walls in the plant kingdom. They have external rings that reinforce the cell, increasing its stiffness and strength.
When coffee is roasted, the increased temperature and transformation of water into gas create high levels of pressure inside the beans. These conditions change the structure of the cell walls from rigid to rubbery, creating a physical change in the coffee. This happens because of the presence of polysaccharides (bonded sugar molecules).
The internal matter pushes out towards the cell walls, leaving a gas-filled void in the center. This means that the beans expand in volume as they decline in mass. Much of the gas build-up is carbon dioxide that will be released after the roast.
Roasting also increases porosity, making the beans less dense and much more soluble.
A very lightly roasted coffee bean remains very hard. If you have every tried to hand grind lightly roasted coffee you will know this. You can barely turn the crank, its like grinding rocks. It is very difficult to extract enough without the coffee being sour and under extracted. All your tools and parameters need to be dialled up to the max.
On the other hand, a very darkly roasted coffee bean has become very brittle, you can easily crush it with your fingertips. It is very easy to over extract and end up with bitter coffee, you need all your tools dialled right down.
There is a whole Roast Spectrum, it is very cheap, quick and easy to measure where your coffee falls on it, by measuring the density.
What is Density?
Volume/weight=density. You weigh 100mls of your roasted coffee beans in a good quality (+/-0.5ml) Graduated cylinder with good scales (+/-0.1g) . The Acaia Pyxis are awesome because they are accurate to 0.01gms and have a very fast refresh rate, or Acaia Lunar. But there is a good range to suit every budget, such as TIMEMORE Coffee Scale Black Mirror Basic Plus 2021 .
For the process see Measuring Coffee Density.
The density has a direct correlation to the Roast Level.
The real world range you see is from very dark roast 100mls weighing as little as 34.0g i.e. 0.340 g/ml; up to very light roasts where 100mls weighs as much as 49.0g i.e. 0.490 g/ml. That gives us 490-340=150 different roast levels measured in 0.1g steps.
Where your coffee falls on that 150 point density/roast spectrum dramatically changes the level of extraction required to hit the sweet spot.
Espresso is a wonderful method of making coffee. It gives you a great set of tools/parameters to manage the degree of extraction. You need to actually vary each of these parameters according to the roast level, not fix them.
In addition, there are supplementary parameters
- Basket size
- Cup size
- Coffee aging
- Grind size
- Bypass water
Every one of these extraction parameters changes, relative to where your coffee falls on that 150 point roast spectrum.
And then of course, least we forget it, you still have to correct for…
I’ll cover each of the tools in turn, and the ranges they take with changing density/Roast Level.
And remember, Don’t look to the left, don’t look to the right
just follow that strait old line…
Water is a powerful solvent. Using your ratio of water to dose of coffee correctly, is possibly the most powerful tool you have, and typically the most under utilised.
Espresso Ratio ranges from 1:1 for a very dark roast to 1:5 for a very light roast.
If you have a very dark roast and try using a fixed 1:2 or 1:3 ratio you will have put through far too much water, over extracting. No amount of grind adjustment can compensate, and you will make a bitter coffee. Which is why most people put a ton of milk and sugar with dark roasts.
At the other end of the roast spectrum if you have a very light roast and try using a fixed 1:2 or 1:3 ratio you will have put through far too little water, under extracting. No amount of grind adjustment can compensate, and you will make a sour coffee. Which is why most people simply don’t even try light roasts on espresso, and use filter methods. But they are missing out, because you can have some wonderful taste experiences with light roasts when they are extracted properly.
Using the right ratio for the for the Roast Level as indicated by the density can make all the difference between success and failure.
Dose means the weight of dry ground coffee.
When changing the Ratios across the 150 point Roast Spectrum, it is really useful to also change the Espresso Dose.
For example, with a very light roast with a 1:5 ratio, a 14g dose produces a just manageable 70g yield of espresso. If you used a larger 20g dose, you would need a massive 100g which exceeds the brew chamber of devices such as the Flair 58. It is much easier to achieve high ratios when you reduce the dose.
With a very dark roast with a 1:1 ratio, increasing the dose to 25g keeps the yield up at 25g.
Using the right dose for the for the Roast Level as indicated by the density helps getting the extraction right.
Yield means the weight of coffee made.
Yield = dose x ratio. For example if your dose is 20g and your ratio is 2.5 then your yield should be 50g. You should be using your scales under your cup and stopping the shot when it reaches the target yield. The important thing to keep constant is the ratio. So if you need to lower the dose to 18g for example, because you cant fit 20g in your basket, then your yield should be 18×2.5=45g.
Higher temperatures extract soluble compounds much more easily than lower temperatures. For espresso the range needs to be from 95 Celsius for a very lightly roasted hard dense bean, down to 85 for a very darkly roasted, porous, low density bean.
Filter coffee has a much longer contact time than espresso, and temperature drops over this time, so the range is smaller, 95 Celsius for lightly roasted very dense beans, down to 90 Celsius for darkly roasted porous beans.
Your coffee is likely to be roasted somewhere between these extremes. The optimum temperature for your roast level will fall somewhere on this scale.
Using the right temperature for the for the Roast Level as indicated by the density helps getting the extraction right.
The interesting thing to see is the mid roasts which fall around 0.400 g/ml require 89-90c, somewhat below the SCA recommended 93c. People are waking up to this fact that mid roasts tastes better at a lower temp than people have been using in their fixed recipes. You can see this in many winning AeroPress competition results.
The Flair 58 sensibly has three temperature settings.
- 1 light = 85 c
- 2 lights = 90 c
- 3 lights = 95 c
For the most common roast levels, people should be using setting 2 of 90c.
Pressure was initially used with espresso to reduce the time taken to make a cup of coffee. The more pressure the faster the extraction. 9 bars of pressure could produce a coffee in 25 seconds compared to a filter coffee taking 4 minutes. Pressure is a range, for espresso 6 – 9 bars is recommended. If you have a lightly roasted dense bean, maintaining 9 bars or pressure helps cope with a finer grind, and is going to help extract the most sugars.
At the other end of the roast/density spectrum, a very dark roasted brittle fragile bean that is easily over extracted, a gentle 6 bars of pressure helps cater for a coarser grind and helps avoid over extraction.
Your coffee is likely to be roasted somewhere between these extremes. The optimum pressure for your roast level will fall somewhere on this scale.
Increasing the shot time increases the level of extraction, so for a very light roast going up to 40 seconds helps.
Conversely with very dark roasts reducing the shot time as low as 20 seconds helps avoid over extraction.
The time provided is for a standard 58mm basket. Small diameter baskets have a deeper bed, and require more time.
VST Precision Filter Baskets
An important aspect of espresso is using the correct ratio for the roast level, which changes the dose, and consequently the basket.
The extremes are a dark roast requires 1:1 ratio, a 25g dose gives a 25g yield. A very light roast requires a 1:5 ratio, a 14g dose gives a 70g yield.
VST Precision Filter Baskets are optimized for use with specific capacities in dose weight of coffee. The size of the holes, the number, and placement, varies across the basket sizes to to deliver consistent extraction performance.
VST basket hole sizes:
VST baskets produce significantly more consistent results than OEM baskets. See https://clivecoffee.com/blogs/learn/portafilter-baskets-do-they-matter
VST Precision Filter Baskets are available in 7, 15, 18, 20, 22 and 25 gram capacities.
All baskets feature…
- Unmatched Quality Control: 100% of holes are measured on every filter for min/max
range and hard limits on area and diameter to a precision of better than +/- 30 µm
- All holes are measured for circularity, placement, square area and blocked holes.
- Filters are matched for total square area opening to +/- 5% to ensure identical group-to-group
performance. (Typical filters vary from -50 to +100%)
- Hole pattern is centered to +/- 1.0 mm and placement is
oriented for uniform extraction throughout the entire puck.
- Wide outlet angle prevents clogging, anti-wear design
ensures uniform extraction performance for life of product.
- Improved structural integrity, 20% heavier than standard filters,
highly polished inside treatment and profile for clean knock-out
Very lightly roasted coffee has required a low dose and a high ratio of water, and some bypass water (as above). If you use a small 5oz/150ml cup, it will taste better than being washed out in a large cup.
At the other end of the roast/density spectrum, a very darky roasted bean is very ashy and burnt tasting. A large volume of milk helps makes a more palatable drink. A larger 8oz/236ml cup will taste better.
Your coffee is likely to be roasted somewhere between these extremes.
Changing your cup size to suit your roast level is recommended.
Age and degassing
Roasting coffee beans causes a build-up of carbon dioxide gas trapped inside the bean, which is released over time after the roast. This is why good coffee bags have a one-way valve that allows carbon dioxide to escape, while preventing oxygen from entering.
If you attempt to use coffee immediately after roasting, you will probably end up with a very sour coffee. There is so much CO2 being given off on contact with the hot water, that it prevents the water penetrating and extracting soluble compounds adequately.
So, you have to wait to use the beans. But wait too long and the beans go stale and lifeless.
The rate beans degas varies considerably with the roast level. With a very dark roast, which is very porous, the beans degas very quickly, and may reach their peak flavour in as little as 4 days after roasting.
At the other end of the roast/density spectrum, a very lightly roasted bean is very hard and dense, it releases gas very slowly and might not reach peak flavor until a month or more has passed.
Your coffee is likely to be roasted somewhere between these extremes. The optimum age/degas for your roast level will fall somewhere on this scale.
The trouble is there are a great number of different combinations and permutations of espresso machines, grinders, burr sets, basket sizes which makes providing a Grind Size almost impossible.
That’s not to say knowing the density can’t help with grind size. If you start recording your own ideal grind settings with varying densities, you will find you can significantly reduce your dialing in time.
The one thing I would say is if you have set all the other parameters correctly (dose, ratio, yield, temperature, and you know the time you need to achieve, then you will need to make smaller changes to gind size, making getting your grind setting about right is easier.
You should always taste test the coffee, even as you make it. Catch the last few drops in a teaspoon and you will quickly see if they are still too sour and you need to grind finer, or if they are sweet.
The grind setting provided is in microns, for my use with Kafatek Monolith MAX with 58mm VST precision baskets. YMMV !!!
I do recommend you get a Kruve Brewler and measure the microns your grinders produce at each setting. By doing this you will also find out how consistent your grinder is – if it produces a range of boulders and fines or preferably not.
Very lightly roasted coffee has required a low dose and a high ratio of water (as above). If you add a lot of milk, as most people do with flat whites, lattes and cappuccinos, then the light delicate flavour notes, fruits, acidity, and aromas, of a lightly roasted coffee can easily be overwhelmed. By replacing a proportion of the milk with some hot water you will bring out the full range of flavours from your coffee beans. This hot water has bypassed the coffee extraction bed (to avoid over extraction bitterness) – hence the term bypass. Commonly bypass is used with Americanos and long blacks. But with an increasing trend to lighter roasted coffee, bypass should start to be included with milk versions as well.
At the other end of the roast/density spectrum, a very darky roasted bean can be very ashy and burnt tasting. A large volume of milk helps makes a more palatable drink; no bypass hot water is required.
Your coffee is likely to be roasted somewhere between these extremes. The optimum bypass hot water for your roast level will fall somewhere on this scale.
Here is some interesting additional information on extraction: Coffee Extraction and How to Taste It – Over/Under Extracted Coffee (baristahustle.com)
Other fields provided on density.coffee:
This is just to give you an indication of where your coffee falls on the 150 point roast spectrum. If 0% is the lightest roast level you are likely to encounter, and 100% the darkest, where does yours fall.
This is information for the coffee roasters.
You’ve probably heard a few roast names. Some refer to the bean’s appearance (Cinnamon), the region it’s from (Viennese), or when it should be drunk (After Dinner).
Despite this, there’s little naming standardisation. Some terms are used interchangeably, others can describe a range of roast levels, and the names don’t always directly reference the coffee’s flavours or aromas.
- Light City Roast
- Half City Roast
- New England Roast
- American Roast
- City Roast
- Full City Roast
- Vienna Roast
- French Roast
- Italian Roast
You are MUCH better off measuring the density to determine which of the 150 Roast Levels you have.
Milk and coffee are a marriage made in heaven. When milk is steamed to 60 Celsius it reaches its optimum sweetness. Aerate it just enough to produce a thick paint texture.
Most people currently use a fixed 1:2 ratio for espresso.
This ratio evolved back in the 60’s when Robusta proportions in blends sky rocketed to 75% in Italy and France due to widespread coffee rust die back of Arabica. Espresso roasts were very dark to mask Robusta’s low-quality flavor and inherent bitterness. The roasts became known as French Dark and Italian Roast.
The 1:2 ratio was an average recipe with 25s shot time that would do.
In more recent times there is much more use of Arabica, and a desire to roast lighter so you can actually enjoy the terroir differences. There is a trend for baristas to use more of a 1:2.5 to 1:3 ratio.
However, the actual sweet spot remains an elusive rarity, because without actually tailoring all the parameters to the actual roast level and 150 levels of roasted bean density, you are unlikely to hit the sweet spot.
You hear of the God Shot, the once in a lifetime perfect espresso.
When people do get to experience a coffee at the sweet spot, the most often response is one of surprise. I’ve given a black coffee to a person who habitually takes milk and sugar, and they were stunned they could enjoy a black coffee.
The same principles of varying filter parameters relative to Roast Level/density apply to Filter Coffee methods.
Filter ratios vary from 1:13 for a very dark roast needing little water to extract, to a very light roast requiring lots of water at a ratio of up to 1:20
I’m using a 480ml Hario Drip Pot with a cloth filter to let through the coffee oils. If tyou try to make a single cup, the bed depth is not really enough, it works better as a 2 cup.
Because of the longer contact time with filter coffee methods, the temperature range needs to be kept higher than with espresso.
Lighter roasts need more contact time to extract, darker roasts need less.
A day out of the freezer = 200 days in the freezer.
I single dose my coffee and freeze it in reusable 70ml pots
Coffee Tools Comparison
A Coffee Refractometer costs about $730 USD. All it tells you, is the Total-Dissolved Solid (TDS) percentage. Maximizing the TDS does not make a better cup of coffee.
In contrast, a 100ml graduated cylinder is cheap ($9 on Amazon). By measuring the density and using SSDI site, you get a brew guide that tells you temperature, dose, yield, ratio, pressure, contact time, optimum age of the beans, and of can even determine the starting grind size. It helps you optimize for sweetness.
Density.coffee is the result of a great deal of research, testing and ongoing revision. It uses computer modelling, predicting over 5000 data points. The computer model has proven to be very successful, to the point that I personally would now not make coffee without it.
In an ideal world, Coffee Roasters who often do 60kg batch roasts, would measure the density for you. You would find the Roast Date, Density and the QR code on each bag you purchase.
But the reality is the use of roasted coffee density is a brand-new thing, and it might take a while to catch on. But you can start using it right now, by getting yourself a graduated 100ml cylinder.
The benefits of measuring density to accurately determine the coffee sweet spot, are a liberating revelation.
It becomes a safe and enjoyable prospect, exploring the wonderful diverse world of specialty single origin coffee, when you no longer live in fear of handling some really challenging light roast.
Do try it (SSDI).