The Chemistry of Chocolate Part 2: General Cocoa Bean Chemistry

Chocolate doesn’t just grow on trees. Well, actually it does…kind of. Chocolate is made from the fermented and dried seeds–often called cocoa beans–of a fruit, a large berry in fact, that grows on a tropical tree between approximately 20ºN and 20ºS. It was once commonly thought that two subspecies of cacao trees existed, Theobroma cacao ssp. cacao—commonly called Criollo—and Theobroma cacao ssp. sphaerocarpum—commonly called Forastero. However, more recent research suggests that the idea of two separate subspecies is incorrect, since though Criollo and Forastero populations certainly have differing phenotypes, they are sometimes far more similar than different, with some Criollo and Forastero populations being much more alike than either is similar to various hybrid populations. We will touch on this issue more in this installment of The Chemistry of Chocolate, as it is quite relevant to the chemistry-based role that genetics can play on the flavor of cacao. First, however, let it be noted that it is common in the chocolate industry, and especially in chocolate marketing within the industry, to talk about the following three categories of cacao: Criollo, Forastero, and Trinitario.

We have already seen the terms Criollo and Forastero, and the name “Trinitario” stems from the hybridized trees of Criollo and Forastero parentage in Trinidad following a “blast”—either disease-based or hurricane-based—in the first half of the 18th century. Because the name Trinitario had relevance in speaking of the first well-known hybrids of cacao, it gradually also came to be used in a generic sense by many people, for almost any hybrid, despite the fact that many hybrids have nothing to do with Trinidad as their origin. Therefore, though in Trinidad there is still said to be true Trinitario cacao, in the sense of it being closely genetically related to the original, and though some of this cacao was spread to other geographical regions, the term is generally more confusing than it is helpful. For this reason, I will not use the term Trinitario, but will use the more generic term “hybrid,” which, though leaving much to be desired, since it lacks the specificity needed to delineate the hundreds—at least—of cacao hybrids that now exist, will serve the purposes of the Chemistry of Chocolate series just fine. Finally, then, for ease of discussion, we can generally say that there are three main categories of cacao: Criollo, Forastero, and hybrids, and within each group there are certainly countless populations with divergences in phenotypes and flavor profiles of prepared samples, and this means that none of these categories can be seen as a single homogeneous “variety.” However, there are also some general rules that can be stated, which are gleaned from a study of the various populations that are generally seen as fitting within the three categories listed above. Let us first discuss Criollo.

We know that Criollo cacao was historically cultivated by the Olmecs–perhaps as early as 1000 BCE– and then the Maya in Central America and Southern Mexico, and it is likely that these Central American cacao populations had originally come from populations in western Venezuela and the surrounding areas, where such Criollo populations continue to exist, though often in slightly hybridized forms. Interestingly, Criollo matures more slowly, produces fewer fruit, and has low disease and pest resistance. With all of these seemingly negative qualities related to Criollo, one might wonder why the Olmecs and those pre-historic peoples who came before them even bothered to propogate it. The answer is likely in the flavor, in that the Criollo cacao populations are generally particularly nutty, mild, lacking bitterness and astringency, and therefore are often more subtle and pleasing as regards flavor. This being the probable case, despite the drawbacks of such cacao, it gradually came to be favored by certain indigenous peoples of Central America, finally making its way from its likely origin in Venezuela, up to Guatemala, Belize and southern Mexico. The underlying chemical reasons for the flavor of the Criollo cacao, which are related to the genetics of this type, are also quite interesting, and will give us a foundation for dealing with the chemistry of the other cacao types.

One clue that helps to unlock the mystery of the general flavor differences between categories of cacao, is that while Criollo seeds have white interiors prior to fermentation and drying, Forastero seeds have purple interiors. The missing purple chemical in Criollo is the same one that colors polyphenol-rich blueberries: a flavonoid bound to a sugar that, when taken as a whole, is called an anthocyanin glycoside. Though this compound itself is not thought to be bitter or astringent, it has been noted that where it is present in cacao, certain other flavonoids are present as well, and in higher amounts than in cacao with no purple pigment. These other flavonoids, such as catechin and epicatechin, tend to be bitter in their simpler non-complexed form, and in their complexed forms, somewhat less bitter but more astringent. Astringency is a dry/puckery feeling in the mouth caused by the higher molecular weight flavonoid polymers–often referred to as tannins–reacting with protein in the saliva and on the tongue, and though always present in cacao, in excess, the sensation can be quite unpleasant.

Interestingly, not only does the relative lack of these particular flavonoids lead to a less harsh product in the case of Criollo, which has about 2/3 of the amount that Forastero has, but the balance of flavor is shifted even further, as other flavor notes within the cacao become more noticeable in the absence of the flavonoid harshness. Therefore nutty, fruity and other positive qualities of the cacao tend to be more noticeable. However, flavonoids aren’t the only bitter chemicals that are present in Forastero. Theobromine, an alkaloid related to caffeine, is also quite bitter, and present in perceptible quantities in Forastero. We will touch upon theobromine in more depth when discussing roasting later in the series, where it will have a large role to play. Another potential difference between Forastero and Criollo cacao, though the amounts of data present to support it are still limited, is that Criollo or Criollo-heavy hybrids may generally have more free amino acids in their composition. This could well play a role regarding flavor differences between Criollo and Forastero during roasting, a possibility that we will also discuss later in this series.

As for hybrids, they can have many different combinations of the above Criollo and Forastero traits. They can seem remarkably similar to Criollo, with only slightly bitter and astringent, very light, pink cotyledons, or they can seem far more like Forastero, with purple, more bitter seeds, and sometimes hybrids can actually include many more bitter and astringent compounds than even average Forastero populations. Hybrids can, thus, not be lumped into one category for the sake of flavor description or internal seed chemical composition, especially since the degree of variation within the whole range of hybrid populations far exceeds variation within Criollo and Forastero populations. This is one reason why, though all three terms–Forastero, Criollo, and hybrid–can be tricky in terms of usage, almost always requiring a bit of supplementary definition, the aforementioned term “Trinitario” is almost useless unless very clearly defined. That said, Criollo also risks becoming a useless term as some people have tended to refer to any hybrid with some amount of noticeable Criollo parentage as Criollo, when, as a hybrid, it obviously cannot be. It is reasonable, therefore, to want to know the whole story behind someone’s usage of the terms Criollo or Trinitario before taking them at face value.

Moving on–so far we have taken a brief look at what role genetics can play in terms of determining cacao chemistry and flavor, but though genetics play a large role regarding cacao flavor, due to flavonoid, theobromine, and, potentially, free amino acid levels, the environment and climate in which the cacao trees grow also substantially impact the chemistry of the cacao seeds and therefore their flavor. As with all fruit trees, the health of the tree itself is important, and so weather patterns that impact temperature, rainfall, humidity and solar radiation levels all play a role in the flavor of the seeds within the cacao fruit. In addition to these various climactic conditions, soil-type, other plant species growing in close proximity–for example shade trees or leguminous atmospheric nitrogen-fixing plants–and even mycorrhizal fungi in the soil that have a symbiotic relationship with cacao, all make substantial impacts on the health, and therefore the cellular chemistry, of the tree and its fruit. In fact, all of these conditions could arguably be combined underneath a single umbrella-term that the French call “terroir”, a word that one normally hears used in relation to grape vineyards and wine. However, it is equally applicable to other crops, and cacao among them. Terroir is responsible, to quite a degree, for the flavor of cacao that comes from different regions, origins, or even given plots of land within regions. Additionally, the various impacts that terroir can have on cacao stretch beyond the growing location and reach into post-harvest processing, as each location, or origin, has different microbial populations that impact the chemistry and flavor of the cacao in dramatic ways. The next part of the Chemistry of Chocolate series, therefore, will delve into this realm of post-harvest processing, as we cover harvest, fermentation, and drying.

3 replies
  1. Anonymous
    Anonymous says:

    As always I enjoy your blog and look forward to your postings. Check your Trinidad “blast” dates. I think it should be mid 18th century (1727?) and not the 19th. The earlier date would make more since why we aren’t sure if blast refers to a disease or a hurricane.

Comments are closed.