Knowing Your Cocoa and Its Quality Parameters: The pH Factor

By Dennis A. Adomako On Feb 19, 2020

OLAM

Whether a liquid is acidic, basic, or neutral is measured by a quantity called pH. pH is a measure of how much hydrogen, in an ionic form, is in a solution.

pH measurements are put on a scale from 1-14, with 1 being the most acidic and 14 being the most basic. If a solution has a pH of 7 it is said to be neutral.

The pH scale is a “power of ten” scale. In other words, something with a pH of 9 is ten times as basic as something with a pH of 8.

There are several techniques used to measure ph. Litmus paper or pH paper is commonly used when the measurements do not need to be highly accurate. pH meters are used when accurate measurements are needed.

In chemistry, pH is a scale used to specify how acidic or basic a water-based solution is. Acidic solutions have a lower pH, while basic solutions have a higher PH.

At room temperature (25°C or 77°F), pure water is neither acidic nor basic and has a pH of 7.

The pH scale is logarithmic and inversely indicates the concentration of hydrogen ions in the solution that is to say a lower pH indicates a higher concentration of hydrogen ions.

This is because the formula used to calculate pH approximates the negative of the base 10 logarithm of the molar concentration of hydrogen ions in the solution.

More precisely, pH is the negative of the base 10 logarithm of the activity of the hydrogen ion. (Bates, Roger G. Determination of pH: theory and practice. Wiley, 1973.)

At 25 °C, solutions with a pH less than 7 are acidic, and solutions with a pH greater than 7 are basic. The neutral value of the pH depends on the temperature, being lower than 7 if the temperature increases.

The pH value can be less than 0 for very strong acids, or greater than 14 for very strong bases. ( Lim, Kieran F. (2006). “Negative pH Does Exist”. Journal of Chemical Education. 83 (10): 1465. Bibcode:2006JChEd..83.1465L. doi:10.1021/ed083p1465.)

pH IN COCOA

The pH of cocoa liquor and cocoa powder is the pH (negative logarithm of the hydrogen ion concentration) of a suspension of these products in water, prepared and measured (Dezaan cocoa & chocolate manual, 40th-anniversary edition, page 33).

Natural cocoa powder has a light brown colour and an extractable pH of 5.3 to 5.8. The processed (alkalized) cocoa powder is darker in colour, ranging from brownish red to nearly black, with a pH from 6.8 to 8.1.

Cocoa Bean Acidity

Cocoa products processed from some samples of cured cocoa beans are found to have a detestable acid taste.

This is often designated as cocoa bean acidity. Cocoa bean acidity has been reported often from Malaysian cocoa.

It has also been found that the beans giving an acid taste to the products generally have low pH. The low pH of cocoa beans is also strongly related to titrable acidity.

It has been established that the organic acids responsible for cocoa bean acidity are mainly acetic and lactic acids.

These are produced from sugars present in the pulp during the fermentation process. Acetic acid produced during fermentation is an essential component of the fermentation process as the acids contribute to the death of the bean, prevent colonization by putrefactive microorganisms, and create an environment conducive to the formation of flavour and aroma precursors within the cotyledons of the bean.

However, excessive quantities of acetic and lactic acids produce an acid taste in the cocoa products, as these are not adequately dispelled in the roasting and conching processes.

The problem of cocoa bean acidity is reported mostly from Malaysian cocoa. The best chocolates are produced from Ghanaian cocoa, in which the acid taste is almost never observed.

Bean pH ranges from 5.3 to 5.5 for Ghanaian cocoa in contrast to a range of pH from 4.4 to 4.7 in the case of Malaysian cocoa. (K.P. Prabhakaran Nair, the Agronomy and Economy of Important Tree Crops of the Developing World, 2010).

Alkalization

Also known as “Dutching,” alkalization consists of the treatment of cocoa mass, liquor, or powder with an alkali. It can also be achieved prior to roasting (Nair Prabhakaran 2010).

Nowadays, alkalization is carried out to improve the colour and flavour of cocoa and to increase the dispersibility of cocoa powder in beverages (Jolić and others 2011; Kothe and others 2013; Giacometti and others 2015).

It reduces astringency by complex polymerization of polyphenols (Afoakwa and others 2008), decreases bitterness, and it darkens cocoa products (Jolić and others 2011).

EFFECTS OF PH ON COCOA

PH in itself helps to reduce the microbial activity in the cocoa as microbes such as Salmonella which cause typhoid fever (Ryan I KJ, Ray CG, eds. (2004), Sherris Medical Microbiology (4th ed.), McGraw Hill. pp. 362–8. ISBN 978-0-8385-8529-0.) find conditions of neutral PH as conducive.

However, our research confirmed the research by others that, a shift in PH affects cocoa as follows:

Lower PH in cocoa (when in an acid medium) increases its sourness (acidity) and astringent (Astringency is a tactile taste felt as a dry, rough feeling in the mouth and contraction of the tongue tissue. From Encyclopaedia of Food Sciences and Nutrition (Second Edition), 2003) taste.
Higher PH in cocoa (when in an alkaline medium) intensifies the dark colour in cocoa and also tends to influence the flavour and taste of the cocoa depending on the concentration.