Marula brew: community brewing to benefit from biotechnology?
Dr Liz Goyvaerts
 South
Africa is home to some of the world's most biodiverse regions with an abundant
variety of microorganisms, plants and animals. Just one of the country's assets
is its many wild fruit trees; some of these are edible, some not, and some like
the marula, are literally a goldmine.
The marula tree (botanical name: Sclerocarrya birrea subsp. caffra)
grows in semi-arid frost-free areas from Ethiopia to Kwazulu Natal in South
Africa. Humans have learnt how to create products from virtually all parts of
the tree; its wood for furniture and making drums, its bark for medicinal
purposes and even its leaves for fodder. And then there are its fruits. The
fleshy fruits are high in vitamin C and are eaten fresh or used in the
preparation of jam, pickles, juice, fermented to beer and distilled to make
liquors and brandies. Marula trees produce several hundred kg per tree on
average but certain trees have been known to produce up to an incredible three
tons of fruits during the season from January to May in South Africa. The dried
fruit skins are ground and provide a cheap alternative to coffee. The two to
three edible nuts of the seed are eaten raw or roasted; from these, a stable oil
is pressed for use in cosmetic creams and as a meat preservative.
 But
wait: there's more. Its benefits do not end there. Marula is the source material
of the famous South Africa Amarula liquor, one of the largest single-product
export earners of South Africa. It is also the source material of the very
popular marula beer sold throughout the season along the Mpumalanga and Limpopo
national routes and taxi ranks. While the Amarula liquor has been successfully
marketed, the limited shelf life of the indigenous marula beer prevents its
market expansion, let alone export. Scientists are now conducting research to
see how biotechnology can work with indigenous technologies to solve this
problem and increase rural income.
Fermentation: an age-old tradition with a new twist
Biotechnology has been around for many centuries. The earliest documented
evidence is the use of fermentation in making breads and  brews
in ancient Egypt and soy sauce in Asia. These early scientists either used
spontaneous and back-slopped fermentation methods. Back-slopping refers to the
process where a little of the fermented product is kept and added to jump-start
the fermentation of another batch of bread or brew. It is the tiny
microorganisms such as yeast and bacteria which do the work, fermenting the
sugars present in the fruits into alcohol and acids.
Community brewers have exploited this process for decades in fermenting
fruits such as marula into marula beer. Marula fruits are first collected and
ripened. Some brewers prefer fruits from specific trees, whereas others are
indiscriminate in their fruit selection. Juice is extracted and left to ferment
for two to four days when the beer is ready for consumption. In addition to the
starting fruit material, the taste of the brew is determined by the particular
set of microorganisms involved in the fermentation and varies from brewer to
brewer and even from batch to batch.
After four days, the beer however deteriorates and develops a vinegary and
pungent smell and taste. Can biotechnology help?
Better bacteria, better beer
Biotechnology allows the set of microorganisms involved in the process to be
rapidly characterized and purified. Pure cultures of bacteria or yeast are
easily isolated using modern technologies and these can each be tested for their
ability to produce a good marula beer. The best cultures can be added to start
the marula brewing process, which will ensure consistency in the fermentation
process as well as the final taste.
The vinegary taste most likely occurs when certain types of bacteria
contaminate the brew. So, changing the process from the present semi-aerobic
(partially open to the air) process to an anaerobic (closed to air) process will
limit the growth of certain types of bacteria, that are responsible for the
production of the vinegary taste and, thus reduce this smell and taste observed
in aging marula beer. The pungent smell most probably results from the death of
valuable microorganisms and the breakdown of proteins in the brew. This problem
can be solved by adding nutrients which actually support the growth of the yeast
and bacteria.
Modern understanding of biotechnological processes such as fermentation means
that just these small interventions can have a large effect. But this is not
possible without the indigenous brewers who have mastered the scientific art of
brewing marula beer for many decades. In the end, a more stable beer can be
bottled and sold over longer periods of time to a larger market, empowering
rural people to participate in the modern economy. So, bringing modern
technology and indigenous methods together is a recipe for success, not just for
better tasting, longer lasting brew!
More information:
See www.pub.ac.za the S.A Public
Understanding of Biotechnology Site for biotechnology news, views and insight.
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