Page 72 - FoodFocusThailand No.244 August 2026

begun once again to pay attention to the coffee’s origin (terroir), down the mucilage. The beans are then washed and dried
variety, and processing method. Roasting has shifted toward to a moisture content of 10–12% before roasting or sale.
light-to-medium roasts to prevent heat from destroying the Traditionally, this process relies on spontaneous fermentation
volatile organic compounds (VOCs), allowing consumers to by naturally occurring microorganisms from the coffee
experience the true flavor of the bean, such as bright fruity cherries, drying patios, and fermentation tanks. Because
acidity or floral aromas. This is also accompanied by a growing these microbial communities consist of diverse bacteria,
preference for more meticulous brewing, namely filter methods molds, and yeasts, their composition and activity are difficult
such as pour-over or drip, which require precise control of to control, often resulting in inconsistent coffee quality.
water temperature and extraction time to draw out the greatest Seasonal changes, together with variations in weather,
complexity and cleanliness of flavor. humidity, and temperature, further influence microbial growth.
Specialty coffee is the term used for Arabica coffee that In the worst case, the coffee may develop undesirable odors,
receives a quality-evaluation score of 80 points or higher, an such as fermented or musty notes caused by the growth of
assessment defined according to the international standard set unwanted molds or bacteria. One widely studied approach to
by the Specialty Coffee Association (SCA). This differs from address this challenge is the use of microbial starter cultures
Robusta, whose specialty grade is called Fine Robusta and is during coffee fermentation, particularly yeast starter cultures.
overseen by a partner organization named the Coffee Quality International research in recent years has found
Institute (CQI); because of the natural differences between the that adding various yeast starter cultures — such as
species, the quality-evaluation methods used differ as well. This Saccharomyces cerevisiae, Kluyveromyces lactis, or
article, however, will discuss only Arabica specialty coffee. The Torulaspora delbrueckii — benefits coffee fermentation in
SCA governs the criteria for evaluating specialty coffee, from several dimensions. 1) It improves product consistency,
assessing green bean quality before roasting to conducting because yeast starter cultures are usually added in quantities
sensory evaluation (cupping). Green beans are lightly roasted large enough to make yeast the dominant microbial
and taste-tested according to protocol by certified tasters known population in the fermentation tank and to prevent other
as Q Arabica Graders, or Q-Graders, who assess the coffee’s microorganisms from growing. 2) It enhances the desirable
cleanliness (free from undesirable odors such as mustiness, flavor of the coffee, because yeast helps break down the
earthiness, or fermented/spoiled notes) and the complexity of mucilage attached to the beans, causing it to decompose
its aroma and flavor (such as fragrance, acidity, body, and so faster, and yeast can also produce a diverse range of volatile
on), with a total score of 100 points. organic compounds that benefit the coffee’s flavor — for
In coffee production, farmers must attend to every detail example, esters, which impart fruity aromas, and certain
of the process from the very start — what is known as “From higher alcohols, which impart floral aromas. 3) It improves
Seed to Cup.” For example, harvesting must collect only fully safety from mycotoxins in the Ochratoxin A (OTA) group,
ripe red cherries to maximize sugar content. Then, in the sorting a carcinogen affecting the kidneys and urinary tract and
and cleaning stage, farmers wash and soak all the cherries in also toxic to the nervous system and liver. Because OTA
water and select only those that sink, because floating cherries is highly heat-resistant, it cannot be destroyed by roasting.
are mostly shriveled, borer-damaged, or underripe. After that, The European Union standard (Regulation (EU) No.
farmers separate the parchment and seeds from the cherries 2022/1370) limits OTA content in roasted coffee beans and
using three popular methods: the Washed Process, the dry ground roasted coffee to no more than 3.0 micrograms per
process (Natural or Dry Process), and the semi-washed process kilogram of coffee (µg/kg). This OTA arises when coffee is
(Honey Process). This article will focus on the washed process, contaminated with molds of the genus Aspergillus, such
as it allows the easiest control of microbial fermentation. as A. ochraceus. One of the most effective ways to reduce
OTA is the use of yeast starter cultures. Yeasts compete with
Yeast Starter Cultures: The Role of Yeast in Coffee molds for nutrients and space, inhibiting their growth, while
Fermentation their cell walls can also adsorb OTA, thereby reducing OTA
In the washed coffee process, the cherry skin is removed, and levels in coffee beans.
the mucilage-coated beans are fermented in clean water for Adding yeast starter cultures during coffee fermentation
12–36 hours to allow microorganisms or enzymes to break is a comprehensive solution for the specialty coffee
industry — from ensuring product consistency and
elevating flavor profiles to make it creating distinctive and
unique characteristics, to improving consumer safety by
reducing contamination with the mycotoxin OTA. Applying
microbiological knowledge with a genuine understanding of
fermentation processes not only adds value to coffee beans
but also represents an important step toward advancing
Thailand’s specialty coffee industry and strengthening its
competitiveness on the international stage.

More Information Service Info C012

72 FOOD FOCUS THAILAND AUG 2026

25/7/2569 BE 16:50
68-72_��������� 3_������.indd 72 25/7/2569 BE 16:50
68-72_��������� 3_������.indd 72