Molecular Flavour profile of Chocolate

Photo credit: Geoseph Domenichiello

This is a summary and discussion of the following article:

Ascrizzi, Roberta, Guido Flamini, Cecilia Tessieri, & Luisa Pistelli. "From the raw seed to chocolate: Volatile profile of Blanco de Criollo in different phases of the processing chain." Microchemical Journal. 133 (2017): 474-479. 

 

The words Esters and Pyrazines are more likely to elicit feelings of apathy rather than appetite.  However, these volatile aroma molecules contained in our food are crucial to our existence.  These aromas lead to flavour, and flavour is what drives us.  World cultures are defined by it.  Our daily life revolves around it.  It unites and divides groups.  It's subjective, and it's fact.  Even a decreased sense of flavour occurring from brain injury or dementia correlates with a decreased quality of life.  Flavour is important. 

Today, a great deal of chocolate in the world often contains what we can describe as one flavour: chocolate.  The rise of monoculture food and agriculture  throughout the world has lead to the acceptance of foods muted in flavour and satisfaction, chocolate included.  However, with the rise of fine & craft chocolate around the world, many can now experience more than just the chocolate flavour from their chocolate.  Today, fine chocolate can be described in a manner similar to fine wine and coffee.  Words such as raspberry, hazelnut, and bread are more frequently being used within our chocolate vocabulary.

There are many skeptics when it comes to this idea of fine chocolate.  Some may feel intimidated because they can't taste these aromas they are told they should taste.  Others discredit the whole idea, and frankly don't care that these aromas may or may not exist.  This idea of highly aromatic chocolate isn't important to everyone, but it does exist.  Nevertheless, appreciating this idea doesn't somehow elevate you above those who don't, but it can heighten your satisfaction with chocolate beyond your expectations. To one individual, chocolate tastes like chocolate, and it's wonderful.  To another person, chocolate tastes like so much more, and that's also wonderful. 

 

analysing the chocolate 

What level of truth is there to these other aromas existing in fine chocolate? Where is the proof? Some may need more than just an "experts" opinion on the flavours contained within a fine chocolate bar. A 2017 study from the University of Pisa analyzed Blanco de Criollo chocolate at the molecular level.  Blanco de Criollo is a dark chocolate bar made by Amedei. Amedei is a well known fine chocolate maker in Italy, established in 1990.  Amedei states the Blanco de Criollo is a rare variety of cacao from Peru.  What's interesting here, is a study that analyzed the specific volatile aroma molecules in a chocolate, and at 8 different stages during its processing.  They then list a profile of the major molecules, and their associated flavours.  

The aromas contained within fine chocolate come from the cocoa beans from which it was made.  These cocoa beans contain the required elements to produce these aromas, which are derived from the tree's genetics and growing environment.  However,  it's the process of chocolate making (properly executed) which determines the final aroma profile.  The 8 stages from which samples in this study were taken are:

  1. Raw fermented & dried cacao beans
  2. Roasted cocoa beans with husk (shell)
  3. Unhusked cocoa nibs (shell removed)
  4. Cocoa liquor (ground up cocoa nibs)
  5. Refined chocolate (processed through 3 or 5 roll refiner)
  6. Conched chocolate
  7. Moulded chocolate
  8. Packaged final product (Which confirmed the packaging didn't alter the aroma profile in any way)

Aroma molecules are categorized into families of molecules depending on their properties.  Each molecule within that family holds specific properties (aroma being one) which are associated with it.  For instance, an ester is a family of molecules that contain many aroma molecules such as ethyl octanoate.  Ethyl octanoate is said to give off a pineapple-like aroma.  This study categorized the identified aromas into 6 families:

  1. Acids (associated with sour/tart/cheese/sweat)
  2. Alcohols (candy, herbs)
  3. Aldehydes & Ketones (fruity/flowery, & musty)
  4. Esters (fruity)
  5. Monoterpene compounds (sweet & floral)
  6. Pyrazines (toasted, burnt, nutty)

In this study, the cocoa beans and chocolate aroma molecules were separated, identified, and explained, offering us an aroma profile of the Blanco de Criollo chocolate bar. The researchers identified the major aroma molecules as well as their quantities.  They observed how at each stage aromas increased and decreased until reaching their final level at stage 7 and 8.  For instance, they observed high levels of acids (cheese- and sweat-like aromas) during stage 1 (fermented unroasted cacao beans), but were eventually undetectable by stage 7 and 8. 

 

The tools utilized

These aroma molecules were identified using 2 techniques:

  1. Gas Chromatography 
  2. Mass Spectrometry

Gas Chromatography (GC):

A tool that essentially separates a mixture into its components.  As you know now, chocolate contains a mixture of aroma molecules from different families.  Each family of molecules are categorized by their unique properties such as molecular size, shape, and weight.  They were analyzing volatile aromas, which are easily evaporated into the air at normal temperatures.  For this reason, they used Gas Chromatography, since the molecules being separated were in their gaseous phase. 

Mass Spectrometry (MS):

This often goes hand in hand with GC.  Once the volatile aromas are separated, they are identified and quantified.  This is where mass spectrometry comes in.  It identifies these molecules based on their mass-to-charge ratio.  It measures the masses, which is unique to each of the molecules.  This will help identify the molecules the GC is separating, and how much of them exist in each sample.  

After these two processes are complete, the researchers have a list of the major aroma molecules contained within the chocolate, as well as how many are contained within the product at each of the 8 stages. They go on to list the major molecules identified, and describe the aromas that we experience when we smell or eat foods that contain them.  

 

What to take from this study

The aroma profile of the chocolate changes at each stage of the process due to heating or mechanical forces.  This suggests that although the variety of cacao and the origin of where it grew is important to flavour, the processes of turning the raw cacao beans into chocolate has a huge impact on the final flavour as well.  This is what a chocolate maker, big or small, must understand if they are to make delicious chocolate products. 

Don't get too hung up on the chemistry jargon used here.  You don't need to understand what a ketone is, or remember that ethyl decanoate is associated with a pear & grape aroma in order to appreciate the following information.  Understand that there are different categories of aroma molecules.  Appreciate that the aromas we describe in our daily lives are associated with particular molecules.  Understand that the way we grow and manipulate our food has a great impact on these "flavour" molecules.  The better we understand this relationship, the more satisfaction we can get from our food. 

That said, if you wish to understand what these terms mean in depth, I won't discourage you from looking them up yourselves.  However, I won't take the time here to define what they are.

 

What was identified in this study

The following will discuss the list of the major aroma molecules identified in Blanco de Criollo chocolate, and categorized according to the family they belong to.  Although all these aroma molecules were identified, their quantity rose and fell throughout the process.  The table below is only part of what was included in the study.  The 8 stages, listed A to H, are at the top, and the aroma molecules are listed on the left.  The numbers under each column are the relative percentages of that specific aroma at each of the 8 stages.  Notice how for instance, 3-Methylbutanoic acid is at 1.7 during the first stage, falls, rises at cocoa liquor stage, and falls again afterwards. 

Keep in mind, that although some of the more favorable aromas appear to be very low by the final stage, those small amounts have a profound influence on our sense of flavour.  For instance, the majority of all the aroma molecules in a fresh strawberry don't give us the perception of the flavour "strawberry."  Those aroma molecules that actually give strawberries their distinct flavour are at almost trace amounts.  So although some fruity-smelling alcohols below may be below 1%, they still can have a huge impact on our perception of their aroma.  

Flavour Aromas de Criollo.png

1) Acids

Cocoa beans are highly acidic, particularly after they are fermented. This acidity is not usually a favourable flavour in chocolate.  Many craft chocolate makers these days are not shy to create chocolate that is tart or acidic.  However, quality flavour is determined by a balance of these acidic flavours, and an overpowering acidic flavour could be more an indication of poorly processed chocolate.  

Often craft chocolate is described as fruity because it tastes tart or acidic.  It's true that some chocolate can be described as citrus, which is often associated with a sour taste.  However, chocolate being sour doesn't necessarily mean it's fruity.  You can enjoy the aromas of raspberry, citrus, and strawberry in your chocolate without the chocolate being too sour.  The tartness should aid and encourage the aromas, not mask them. 

Acidic chocolate often indicates hiccups during processing.  The acid aroma molecules are biosynthesized by the bacteria during fermentation of the cocoa bean.  The bacteria lowers the pH of the cocoa bean from 6.3 to 4.5-5.8.  However, over or improper fermentation will increase the acidity beyond prefered levels.

The acids evaporate during the drying and roasting stages.  Roasting influences the evaporation of these acidic aromas.  However, if dried to quickly, the husk (or shell) of the cocoa bean can dry too quickly and become less permeable.  This doesn't allow acids to evaporate from the kernel.  These acids are also released after the husk is removed, confirming the idea that the husk, although thin and permeable to acids, can also restrict their release dried too quickly.  Heap fermentation in particular (a form of fermenting that differs from box fermentation) tends to increase the level of these acids. 

Acids identified by Ascrizzi et al. were:

Flavour Aromas de Criollo.png

3-methylbutanoic acids = described as rancid and cheesy

2-methylbutanoic acids = rancid and sweaty aroma

Luckily as mentioned, these acids are released and drop to very low levels in the final product. 

2) Alcohols

These are produced when the carbohydrates in the kernel (cocoa nib) are broken down during fermentation.  High amounts of volatile alcohols tend to give off candy and flowery aroma notes.  

The amount of volatile alcohols increase from the raw cocoa bean to their highest point in cocoa liquor (when cacao beans are ground up into a paste), then levels begin to drop afterwards. 

Alcohols identified were: 

Flavour Aromas de Criollo.png

2-heptanol = citrus and lemon grass

phenylethyl alcohol = flowery, spicy, and honey-like

These two are relatively stable during the process.

 

3) Aldehydes & Ketones

Aliphatic aldehydes tend to be associated with fruity and flowery notes. 

The molecules detected were:

Flavour Aromas de Criollo.png
flavour aromas de criollo 2.png

2-methylbutanal = malty & chocolate 

Benzaldehyde = bitter (luckily is unstable, and decreases during processing)

2-phenyl-2-butenal = sweet, roasted, rum, & cocoa

5-methyl-2-phenyl-2-hexenal = sweet, roasted, rum, & cocoa.  This molecule i the major odour compound in cocoa powder.

acetophenone = sweet, flowery, almond- & must-like.  This molecule is increased during the roasting stage. 

2-heptanone = cheese-like & unpleasant.  However, this is undetectable after conching, as that process turns it into the alcohol 2-heptanol (citrus/lemon grass) mentioned above.

 

4) Esters

Esters are a major component to the flavour of chocolate. They are the second most important chemical group to cocoa after pyrazines.  They generally elicit a fruity aroma.

The main aromas found were:

flavour aromas de criollo 2.png

Ethyl octanoate = pineapple like

Ethyl phenylacetate* = honey (*considered one of the most important components in the cocoa aroma)

Ethyl decanoate = pear and grape

These first three are fairly stable throughout the processing of chocolate, and tend not to increase or decrease too greatly.

2-phenylacetate = rose & honey.  This molecule is quite unstable, yet gives off a delicate favorable aroma.  

It was noted that it's desirable to have high concentrations of ethyl phenylacetate and 2-phenylacetate in chocolate. 

 

5) Monoterpene compounds

These molecules give off a sweet and floral like aroma, especially the oxygenated ones.  

The aromas identified were:

flavour aromas de criollo 2.png

linalool = flowery

trans-linalool oxide = floral, evident in all 8 stages

 

6) Pyrazines

Pyrazines are the most represented flavour in foods which are characterized by toasted, burnt, and nutty aroma notes.  They are contained in foods processed under high temperature & low humidity, which are favorable to the Maillard reaction.  The Maillard reaction is where proteins and sugars mary and produce an incredible array of flavours in our foods.  The browning of baked goods, seared meats, and vegetables, are evidence of the Maillard reaction.  

In chocolate, pyrazines are the most represented flavour.  Up to 84.8% as seen in this study at the conching stage.  

The aroma molecules identified were:

flavour aromas de criollo 3.png

Tetramethylpyrazine (TMP, 26) = green aroma with coffee & cocoa-like attributes.  Significant levels of this within chocolate often identify the criollo variety.  It is derived from fermentation (via bacteria), not from heat treatment (Maillard reaction) as other pyrazines are (as stated above).  This is aroma is often achieved after a medium roast. 

2,3,5-trimethylpyrazine (TMP, 16) = green, earthy, cocoa, & roasted nuts

2,5-dimethylpyrazine (DMP, 10) - cocoa and caramel.  DMP, 10 is a good indicator of the degree of roasting.  This aroma is often only achieved after a darker more extreme roast. 

 

Let's Sum it up

You now have some evidence of the aromas contained within fine chocolate.  You can see from the data in the tables that the levels of these molecules are constantly shifting due to how the cacao beans and chocolate are processed.  Although anyone can grind up cacao beans and make chocolate, not everyone has the skill involved to do it well enough to allow for these array of aromas.  

Faults in processing chocolate, such as over fermenting (acidic flavour or mould), over roasting (burnt), under roasting (acidic), and over conching (bland), can lead to higher levels of unwanted aroma molecules listed above, and lower levels of the favorable ones.  It's very important to understand how to process chocolate, and what to look for (and taste for!) when processing.  Although as a consumer you likely won't be making the chocolate, understanding why your chocolate tastes the way it does can help you become a better judge of chocolate makers out there.

Remember, this was just one specific variety of bean, from one origin (Peru) by one maker (Amedei).  Other chocolates made from Amedei, or the same beans processed by another maker would result in a different aroma profile.  There are countless varieties, origins, and makers out there to bring you an incredible array of delicious aromatic chocolate.

Hopefully dissecting this study has helped you understand the complexity of fine chocolate, some aspects that dictate flavour and quality in chocolate, and more importantly has raised new questions for you to take on your quest of understanding chocolate!

Salute!