Sugars in roasted coffee – a conversation

August 6th, 2010

I’m posting this (with consent of the other conversants) in an effort to kickstart some more open discussion about roasting. Right now there is very little out there when it comes to roasting speciality coffee. I am aware that most of the studies quoted below were probably done on C-grade coffees.

I hope we can get to a place where we can discuss profiling, roast development, densities and the like with a view to understanding what we do better and to reduce the time we put into trial and error profiling. Undoubtedly lots of great roasters aren’t just heating and hoping – they are applying a lot of what they’ve gained from previous experience and other knowledge.

Below is an email exchange between Deaton Pigot, Chris Kornman (both roaster with Intelligentsia) and myself. It had come about after a comment I’d made on someone else’s blog about there being no sugars in roasted coffee.

As becomes evident in the exchange – there really is a need to better define what we are talking about when we use the term sugars.

I wish I could say that all my emails are like this, that every day is an in depth discussion of theory combined with our experiences.

Unfortunately this conversation didn’t get any further – work has a terrible way of getting in the way of things like this. I can only speak for myself here, but feel free to pick apart things I’ve gotten wrong or misunderstood. If people would like to contribute anything – please post in the comments.


From: Chris Kornman [mailto:xxx@xxx.com]
Sent: Thursday, January 21, 2010 11:43 AM
To: Deaton Pigot
Cc: xxx@xxx.com
Subject: Re: This is interesting

So we got interested in this “no sugars” claim by JH below, and Josh &
I did some digging.

Sucrose (aka white table sugar, chemical formula C12H22O11) has a
melting point at around 370F (so sucrose, if present in coffee, would
caramelize at or before 1st Crack.) It breaks down into water vapor
(H20) and carbon dioxide (C02).

According to our colleagues Henry Schwartzberg (Professor Emeritus,
University of Massachusetts) and Joachim Eichner (Praxis International
Inc), during the roast, Polysaccharide (Starch chains containing sugar
polymers) Hydrolysis (water breakdown that splits polymers) in the
cell walls of roasting coffee results in the creation of sugars and
oligosaccharides (simple sugar chains). Also, sugars break down to
form Aliphatic (fatty) acids.

So roasting both creates and decays sugars.

Rapid decay begins later in the roast, (11min according to HS & JE),
so likely during or after first crack. The decay of sugars also
produces alcohols & furfural (“…an aromatic aldehyde… Its chemical
formula is C5H4O2. In its pure state, it is a colorless oily liquid
with the odor of almonds, but upon exposure to air it quickly becomes
yellow” – Wiki).

It seems unlikely that full degradation would take place before the
end of 2nd crack, however.

So, yes, there are sugars in roasted coffee.

-ck


On 21 Jan 2010, at 20:11, Deaton Pigot wrote:

Hey James,

I am emailing you because of your comment on the Double shot blog about
sugars left in coffee after roasting. I am sure all of us would love to hear
your thoughts on our mail chain. That is of course if you have the time to
answer.

Hope you are well!

Kind regards

Deaton

Chris and Josh that is a great read! Out here we (or at least I) have bought
into the Staub theory of developing sucrose. IE Polysaccharide split into
monosaccharide, creating a foundation of sucrose that would essentially be
dug into the later stages of the roast.

I went into it in some detail here

http://deaton.wordpress.com/2009/07/12/balancing-act-sweetness/

Plus some of it here as well.

http://deaton.wordpress.com/2009/05/07/how-sweet-is-your-cup/

I know that in James comment he stated;

“Nothing to do with sugars – of which there are none left in roasted coffee,
certainly not simple sugars which react away through maillard, caramlisation
and strecker degradation reactions.”

So it leaves me wondering what sugars he believes are left in the bean after
roasting, as we all know we do perceive varying levels of sweetness.


From: James Hoffmann [mailto:xxx@xxxx.com]
Sent: Thursday, January 21, 2010 2:13 PM
To: Deaton Pigot
Subject: Re: This is interesting

Hey Deaton,

I could well be wrong – it’s usually the case.

I will dig out the reading I’d done on this – by sugars I meant simple sugars, rather than long chain complex carbohydrates.
No doubt there is sweetness, but more things than simple sugars create the sensation of sweetness on our tongue. Sweetness reception, like bitterness reception, is complex and only reasonably understood.
I find the sweetness of coffee to be unlike the sweetness of simple sugars. I’ve had very sweet shots, for example, but not ones I would describe as sugary.

Give me a day and I will either get pwned or add something interesting.

Kind regards,
James Hoffmann


From: James Hoffmann [mailto:xxx@xxx.com]
Sent: Thursday, January 21, 2010 3:39 PM
To: Deaton Pigot
Subject: Re: This is interesting

Hi Deaton,

I think the tricky one here is going to be pinning down a useful definition of sugars.
Once polysaccharide chains get longer they are perceived as being less and less sweet. In the past i used an 18-chain multidextrose to make non-sweet syrups.

The simple sugars, as would be perceived as having a strong sweetness, are very reactive during roasting – through maillard, strecker and caramelisation. Certainly there are some longer chain sugars in the mix.
Most of the research has been done on lower quality coffees, which will always leave us a little in the dark I guess.

Having dug through a couple of textbooks I am up to the following to support my initial statement on the lack of sugar in roasted coffee. If you want the full paper titles referenced then let me know and I will dig them out.
When talking about sugars I am talking about low molecular weight carbohydrates (R.J. Clarke’s definition). On a side note – related to the original post – it seems Petracco et al (1999) isolated a polysaccharide that actually increased foam stability. I digress….

Trugo & Macrae (1985) did a study that showed 97% sucrose loss in light roasted coffee, creeping up to 99% in a dark roast. Hughes and Thorpe (1987) came up with 0.24% and 0.34% sucrose in roasted coffees. Sucrose can hydrolise into glucose and fructose but both degrade thermally more readily than sucrose.
Noyes and Chu (1993) found 0.1% sugars in 21 roasted Brazilian coffees – though most of this (0.08%) was sucrose.

My reading implies that most of the polysaccharides in coffee are extremely stable through the roasting process – according to Bradbury and Halliday (1990), and hydrolysis would have to happen at lower temperatures when there was still water available. I couldn’t find data on water activity and roasting temperatures – to understand when hydrolysis would stop. Will keep looking.

I guess what I would look to argue is the breakdown of the polysaccharides – which ones are breaking down, into what size chains? Do these chains have detectable sweetness? What molecular weight do we use to decide a cut of point for sugars?

Food for thought…..

Kind regards,
James Hoffmann

Related Reading

For reference this older post on the Maillard Reaction, Strecker Degradation and Caramelisation may be of interest.

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