Plants & Human Affairs - Introduction
Cherries.wmf (7140 bytes) Plants & Human Affairs (BIOL106)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321;;

Beverage Botany

I.  Introduction
            Do you stumble out of bed and immediately reach for a cup of coffee or tea?  If so, you’re not alone.  Millions of people around the world start their day with a cup of coffee.  This class takes a look at some of our important, non-alcoholic beverages.

II. The importance of plants
   Virtually all of our culturally-important beverages, with the exception of milk, are derived from plants.  Although many plants are used to prepare beverages, few are of major significance. 

III.  Preparation of beverages
   Two main techniques are used to prepare non-alcoholic beverages:  

  1. Juice - the plant material, usually a fruit, is pressed or chopped to release the juice.  Except for a sterilization stage, the resultant beverage usually undergoes no additional processing.  Examples include the juices of apple, cranberry, citrus, pineapple, tomato, and carrots; and

  2. Decoctions - the plant material, typically leaves, is steeped in water.  After a suitable period the liquid extract is separated from the spent plant materials.  In many cases the plant material undergoes considerable processing before it is ready for extraction.   Coffee, tea, and mate are good examples of decoctions.

IV.  Biologically activity
   All of our commercially important beverages are biodynamic.  In other words, they exert a physiological influence on our body.  For example, many are caffeinated (e.g., coffee, tea, chocolate, mate), but only a few are not (e.g., fruit juices).   The former is by far the most commercially important type.  Alcohol is a depressant of the central nervous system.  In contrast, caffeine is a stimulant.   Among its actions, caffeine stimulates heart rate, increases acidity in the stomach, increases metabolic rate, and mimics the effects of adrenaline.

V.  Coffee

A.  Taxonomy

   The word coffee is derived from the Arabic word, “kahwah”, which refers to the bitterness of the beverage.  Coffee belongs to the Coffee (or Madder) Family, Rubiaceae.  There are 3 major species, Coffea arabica; C. canephora (robusta); and C. liberica.  C. arabica is the most important species and accounts for at least 80% of world trade.

B.  Origin

   Coffee is originally native to Ethiopia (mountainous regions of the southwest). 

C.  Growth Conditions
   Coffee prefers cool temperatures and adequate moisture (ca 60 inch/year).  It grows well in the American tropics (Brazil, Columbia, Central America) and Africa.   The environment is important for flavor.   For example, Jamaican Blue Mountain has a reputation for high quality.  As a generalization, the quality of coffee is: Central America > Columbia & Jamaica > Brazil > Africa.

    Coffee in Central America was traditionally grown in shade, under other trees (nurse trees).  In fact, traditional plantations look similar to the native rainforest.  This provided habitat for birds and other wildlife.  Newer, sun-loving varieties of coffee are much higher-yielding than the shade coffees which means that the nurse trees have been removed and the complexity of the forest system has declined.  One adverse effect has been a decrease in our local birds that overwinter in central America.  Peace coffee is a “shade coffee” that is being marketed to address this situation.

D.  Comparison of species

Comparison of C. canephora (Robusta coffee) and C. arabica (Arabica coffee)




Area cultivated

Western Africa

Columbia, Central America

Volume of World Trade



Plant size

Large, robust







Mild, more delicate


Instants, decafs, blends

Fine sipping coffees




Crop production

2 – 3 crops/yr

1 – 1.5 crops/year

E.  Coffee Anatomy
   The seeds, called "beans", are used to prepare coffee.   The beans develop inside a berry, called a “cherry”.  The cherries, each of which has 2 seeds, are harvested by hand, because they ripen non-synchronously.   This is a very labor-intensive process.

     The seeds are surrounded by a whitish seed coat, called the silvery skin.   Surrounding both seeds is a parchment-like layer.  Finally, this is surrounded by the pulp of the berry and the skin of the berry.  This type of fruit is called a drupe and is similar to a cherry or peach.

F.  Coffee preparation
   Cherries are picked.  The layers surrounding the seeds are removed by:

  1. Dry method  - older, traditional method, common in Africa where water is scarce.  The  dry cherries � mechanically abraded to remove layers.  This process is usually considered to produce an inferior product and is used in Indonesian and some Ethiopian coffees.

  2. Wet method (Columbian, Costa Rican, Guatemalan, Kenyan, Mexican, Kona coffees):  berries in water  ripe berry floats, debris & unripe material sink pulping machine frees seeds from pulp  controlled fermentation, 12-24 hour, chemical reactions removes remaining pulp, mucilage, etc.  wash dry  mechanical remove of endocarp in special mills seed coat (silvery skin) removed by polishing  sized, graded → roasted

     About 5 pounds of berries yields 1 pound of seeds, and there are about 2500 cherries per pound.

 G.  Roasting
   Brings out the flavors, develops the aromas, and releases the essential oils by breaking cell walls.  The temperature and length of roasting determines the ultimate flavor.  Dark roasts are heated longer and to a higher temperature than light roasts.    Roasting degrees:  cinnamon roast < American roast < Full City (dk brown, no oils) < Vienna < French < Italian.  Thus, French roast is a darker, more oily bean than, say the American roast. 

H.  Coffee Rust - (Hemileia)
   This is a fungal pathogen of coffee plants.  Arabica plants are susceptible.  This disease has had a major impact on coffee growing.  For example, Sri Lanka was once a major coffee producer but this fungus wiped out the plantations.  The net result is that tea was substituted, and it fueled the British love of tea.    Robusta coffees are resistant to the fungus and are typically grown in areas (i.e., Old World) where the disease occurs primarily in areas where no rust. 

I.  History
    Coffee has had a rapid rise in popularity.  It was little used 2 centuries ago.  Now it is an important beverage for 1/3 of the world's population.  Coffee passed from Ethiopia
Yemen Arabia Syria, Turkey, Egypt by 1500's Europe by 1600's Dutch established plantations in Ceylon (Sri Lanka) / Java in East Indies 1723 to New World (Gabriel Mathiew de Clieu brought plants to Martinique).

J. Decaffeinated Coffee
   Arabica beans are typically about 1% caffeine by weight, but Robusta beans have twice that amount.  The caffeine can be removed from the bean by a variety of methods: 

  1. Direct contact method - in this process the green beans are steamed to soften them, extracted with methylene chloride to remove the caffeine, then steamed and heated and dried to remove the solvent;

  2. Hot water extraction - this removes the caffeine, but lots of other goodies.  The liquid is then extracted with methylene chloride (or ethyl acetate) to remove the caffeine.  The solvent is evaporated and the remaining materials are reunited with beans;  and

  3. Water process - this is similar to the process above, but the caffeine is removed from the extract by passage through activated charcoal/carbon filters.  The remaining extract is added back to beans.

 K.  Instant coffee.
brewed under pressure (seal in flavor) add aromas as necessary freeze dry or spray nozzles from tall tower, dries as it falls.

VI.  Tea -   more people drink tea than coffee, but tea has less global commercial importance.

A.  Taxonomy
   Belongs to the Tea family (Theaceae).  Tea is an evergreen tree in the genus Camellia, or Thea according to some botanists.  There are three commercially important species:  C. sinensis - low growing, China;  C. assamica - high yielding, India, Sri Lanka;  and C. cambodensis - less important

B.  Origin

   Tea is native to SW China and NE India to Cambodia

C.  Growth
Tea prefers a warm climate.

D.  Harvest
By hand, usually by women and children who wear a basket on their back.  The tip of the twigs with 2 leaves is broken off.

E.  Types of tea:  

  1. Green tea.   Leaves harvested and dried immediately leaves are rolled → further drying.  Some familiar examples are Gunpowder and Imperial Hyssom teas.

  2. Black tea (fermented, preferred drink) leaves are withered (indoors on ventilated racks.  This step makes it easier to break the leaf cells and extract chemicals like polyphenols) roller machine crushes cells frees juices, allows enzymes (oxidases) to oxidize polyphenols fermentation rooms (allows for development of color and aroma; several hours fired (heating reduces the water content) is moved on conveyers through hot air chambers turns black → sifted and sorted and packed.   This comprises about 78% of world’s tea and is most familiar tea type in north America.

  3. Oolong tea - this is a semi-fermented tea.  The leaves undergo a preliminary sun drying and are then rolled.  This type is particularly common in Taiwan and S. China.

 F.  Tea quality.
   Depends on cultivation, processing, environment (rainfall, elevation).   Tannins provide body (color and pungency).

G.  Medicinal Properties.
   Recent research has shown that tea has anti-cancer properties.  One of its constituents, epigallocatechin gallate inhibits the formation of free radicals, that can cause cancer.  

VII.  Cocao - Chocolate

A.  Taxonomy
    Cocao is derived from the chocolate tree (Theobroma cacao), which belongs to the family Sterculiaceae.  The scientific name, which literally translates as “god food”,  was given to the plant by Linnaeus in 1753.  The word “chocolate” is derived from the Mayan words for plant - Coahuatl; and drink - Xochatl.

B.  Origin
    The native home of the chocolate tree is the Amazon basin (i.e., eastern Andes).

C.  Growth
    Cocao is now grown in Central America, S. Mexico, N. South America, and Africa (Ghana, Nigeria, Ivory Coast).  In fact, the over one third of the world crop grown in Africa.   Cocao grows best in wet tropical regions within 17 degrees of the equator.

D.  Some history
    Chocolate was originally drunk.  Roasted beans were put in earthenware pots, ground up to a paste with water and spices and then whipped into a frothy consistency.  Spaniards introduced the drink in sweetened form to Europe.  In fact, Columbus brought it back to Spain on his 2nd voyage, but it wasn’t until Cortez returned to Spain in 1528 that chocolate became popular.

E.  Botany
    Cocao is a small understory tree.   The tree produces seeds in football shaped fruits that are attached directly to the trunk (stem) of the tree.  Each pod, which as a hard melon-like rind and a mucilaginous inner layer, has 30-50 seeds.  There are about 20-50 pods per tree.  It takes about 50 seeds to make ca 100 g chocolate bar.

    Other components in the seeds include:   50% cocoa butter; 15% starch; 15% protein; 3% theobromine; and a trace of caffeine. 

F.  Processing
Pods harvested
 opened with machete seeds scooped out (the pulp is sweet and can be eaten, though some are allergic to it) the seeds are fermented in piles (the fermentation is carried out by the naturally occurring bacteria and fungi) for 5-7 days chemical changes develop flavors (and frees seeds from pulp) kernel changes from tan to purplish kernel is dried transported to point of manufacture seeds cleaned roasted to develop flavor shelled (remove seed coat):  (a) The shells are mulched or extracted for theobromine) (b) nibs (cotyledons) ground to paste (heats up and melts) → chocolate liquor can be molded for baking squares (or expressed to release cocao butter and cocoa powder, drinking chocolate).  The cocoa butter can be mixed with chocolate liquor, sugar, and with or without milk, ground further (and agitated, called conching) for several days at 130-200 F to remove acidic and astringent flavors that develop during roasting.  The chocolate powder is often “dutched” - treated with alkali to improve the flavor.  The cocoa butter is mixed with the chocolate liquor and milk sugar to make chocolate. 

VII.  Mate (Ilex paraguariensis)
Mate is in the Holly family, the  Aquifoliaceae.  It is native to south America - Paraguay, Argentina, and Brazil.  The leaves are dried, crushed, are made into a tea.  Mate is traditionally prepared in gourds (a mate) and the resulting infusion is drunk through a silver straw (bombilla). 


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Last updated:  12/10/2008     � Copyright  by SG Saupe