Let's get down to business

Dear readers,

It has been such a long time! But here we are again, continuing the most interesting blog on the internet. Coffee! Here I am, sitting behind my desk with a cup of coffee, thinking about what you guys would like to read. And you are going to read a lot, that I promise. Before I will talk to you about the fun part of coffee, I think it is best if I give you guys some background information. You never know, it can come in handy one day.

The scientific name of the coffee plant is Coffea and is a genus (which is a taxonomic rank used in the biological classification of living organisms) of flowering plants. Coffea is a perennial plant which means that it persists for three or more years or growing seasons. They typically flower each year but may reamin vegetative throughout their lives. The seeds that we call the coffee beans are used to make the coffee. The scientific name of the coffee bean is Coffea Arabica. Coffea Arabica grow on shrubs (medium-sized woody plant) or small trees that are originaly growing in tropical conditions.

I will show you quickly the Scientific classification:
Kingdom: Plantea
Order: Gentianales
Family: Rubiaceae
Subfamily: Ixoroideae
Tribe: Coffeeae
Genus: Coffea L. 

The picture below shows you what coffee trees look like. You thought they were bigger didn't you? Luckely you have me, I'll explain you everything ;)

Coffee trees

Morphology
First we are going to take a look at the Morphology of the plant. The morphology deals with the form and structure of plants. The typical features of the plants morphology are the flowers, roots, stems and leaves.

Monocots and Dicots

Coffee flower

Monocots and Dicots are two important groups crop plants. The names are derived from the numbers of cotyledons in a plant. Cotyledons are the first leaves formed in a seed. Monocot stands for one and Dicot for two.  A coffee bean is dicot and this means it has two cotyledons.

Dicots

The picture on the left explains what a dicot excists of. If you look closely to the picture with the coffee flowers you can count five floral parts. When looking at the coffee

Coffea cherries

bean you can see that it is split in two, which shows you the two cotyledons.

                           

Coffee Beans

Root morphology
A plant species can be organized in having either a taproot or fibrous root system. A taproot system is usually a large main root that has small lateral roots. A fibrous root system consists of several main roots that each branch and develop many lateral roots to form an interwoven mass. Grasses typically have highly branched fibrous root systems. The coffee plant consists of a tap root system. The tap roots can extend no further than 30-45 cm. The lateral roots can extend 2m from the trunk. The coffee plant consists 80-90% of fibrous roots.

Indeterminate growth
A coffee plant keeps producing vegetation and new flowers after the first flowers are produced. This means that we do not have to cut the coffee plant after we have harvested the coffee beans. Lucky us. Would have been a lot of work to plant a new coffee tree everytime we would have harvested it.

Anatomy

Coffee Bean
 
First I will explain how a coffee bean is build up.

Coffee Berry

1. center cut
2. bean (endosperm)
3. silver skin (testa, epidermis)
4. parchment (hull, endocarp)
5. pectin layer
6. pulp (mesocarp)
7. outer skin (pericarp, exocarp)

A coffee bean is the seed of the coffee plant which is the pit inside the red or purple fruit. These fruits are called the coffee berries. It contains two stones with their flat sides against eachother. Most of the coffee bean consists of endosperm which contains the most important thing of the coffee bean, the caffeine!

The flowering of the coffee plant
 It takes about three to four years for a coffee plant to grow, before it starts producing coffee beans. When the trees start flowering, you can smell something very sweet. The flowers start growing in clusters in the axils of the coffee leaves. Fruit will be produced in the new tissue only. The Coffea Arabica plant is self-pollinating which means it can fertilize itself. When all the coffee flowers are fertilized, it takes about 6-8 weeks before cell devision will occur and the coffee fruit will remain as a pin head for a period that is dependent on climate. Then the ovaries will develop into drupes in a rapid growth period that takes about 15 weeks after flowering. During this period the integument takes on the shape of the final coffee bean. The endosperm will stay very small up to 12 weeks after the flowering. During this time it will suppress, consume and replace the integument. The endosperm will have completely filled the cavity made by the integument 19 weeks after flowering. During the next several months the endoserm will gain dry matter and will attract more than 70% of the total photosynthesis produced by the coffee tree. The coffee cherry will in the end change from green to red about 30-35 weeks after flowering.
If you click the following link it will be explained again: http://www.coffeeresearch.org/agriculture/beandevel.htm

Carbon Fixation
Where does a coffee plant gets it's energy from? Right, from photosynthesis. This is the process by which plants convert energy from sunlight to chemical energy. This energy is used for all other metabolic processes. So it is pretty important. What is needed for this photosynthesis? First of all you need sunlight! and to add up to that you need carbondioxide and water.

Photosynthesis can be divided into two types of reactions: the light reactions and the carbon fixation (dark) reactions. I will only talk to you guys today about the dark reaction, because coffee is dark.
So, carbon fixation... If we want this reaction to occur in a coffee plant CO2 needs to diffuse in the air through open stomata into the chloroplast within the mesophyll cells of a leaf. Gee, that were a lot of difficult words in one sentence. But after that is done it get's easier. Before the dark reaction we first have the light reaction, and during that reaction ATP and NADPH are made which will be used in our dark reaction to convert CO2 into simple sugars. This we call the Calvin Cycle, or C3 cycle.

Photosynthesis in C3 plants is most effective at temperatures from 10 - 25 degrees celcius thereafter. But as I told you before the coffee plant does it's photosynthesis in an effective way because the coffee beans take care of 70% of the total photosynthesis in a coffee plant.

 Nitrogen fixation
Nitrogen is one of the most important elements for plants and is the most limiting nutrient in terrestrial environments.  I wanted to teach you guys all about it, but it was hard to find information about it looking at the coffea plant. The only thing I found was this.

It was observed in free-hand section, that Coffea arabica L., showed an abundant symbiotic bacterium in the parenchyma cells of the stem, petiol, leaf and root. The bacterium was characterized by its motility. The culture always showed a white pellicle below the surface of the Na-malate agar. The bacterium was catalase positive and showed ability to reduce triphenyl tetrazolium chloride. Coffea arabica L. roots showed a very active triphenyl tetrazolium chloride reducing ability that could be associated with the capacity of the tissue for fixing nitrogen!

So to conclude, they think that the Coffea arabica L. is able to fix nitrogen.

I think I have talked enough for today, and that there is enough information to process. You will hear from me soon, and I want to wish you all a very happy new year (in advance). See you guys next year.

Kind regards,
Suzanne