A Coffee Experiment

Experimenting With Coffee
By Aunt Alice

Coffee Liquor- Quality

The quality of coffee liquor in determining the quality of roasted coffee in Kenya, is as important as the quality of the raw bean. Acidity, body (a solutions thickness or viscosity) and flavour, are the three factors presently recognized as important in determining the quality of brewed coffee.

The soluble content of coffee does greatly influence these quality parameters, and there is no doubt that these factors demand proper understanding, to enable the implementaion of quality oriented practices

As regards quality the Kenyan coffee farmer has always tended to be perfect. Quality production has been encouraged by payment on basis of quality and not quanity. This approach has demanded lots of effort in search of factors, that make a cup of quality coffee, as well as advanced procedures for the assessment of quality.

Presently the liquor qualities are assessed subjectively by experienced tasters. This practice is common with producers concerned with quality and marketability.

Objective methods of food quality measurement are preferable to sensory measurements. Objective tests can provide a precise measure of a subjective quality.

Fundamental instruments allow some basic property measurements to be made in search of a better correlation and explanation of sensory characteristics.

Viscometry which is a measure of behaviour of solutions under stress, may be important as a basis for furthur investigation of coffee brew quality.

Below we take a brief look at Viscometry.

Below is a table showing PH and Temperature of freshly pulped coffee, after being fermented, while drained of water for 48 hrs.

Temperature in degrees centigrade, graph of producton of propionic acid production during fermentation

Study Of Coffee Viscometry

The purpose of this study is:

(A) To establish effects on coffee quality when the fermenting coffee is subjected to the following treatment.

(1) Coffee subjected to dry fermentation for 48 hrs and 72 hrs.

(2)Coffee subjected to wet fermentation for 48 hrs & 96 hrs.
.

(3) Coffee washed every day in the course of fermentation.

(4) Coffee not washed at all in the course of fermentation.

(B) To detect the prescence of propionic bacteria in over fermented coffee. This bacteria has been reported to be involved, in the production of propionic acid. This acid is associated with the presence of onion flavour.

Onion flavour

The taste and smell of onion may develop in coffee during fermentation. It is an off flavour associated with the presence of propionic acid in the fermenting medium. The conditions favouring propionic acid formation may also induce onion flavour these conditions include

Prolonged Fermentation

No propionic acid has been detected in fermentation of less than 40 hrs. Traces are only found after 60 hrs and are too low to induce the taint. fermenataion beyond 72 hrs have been reported to give onion flavour

Propionic Bacteria

This bacteria is involved in the production of propionic acid it has also the folowing characteristics.

1 Gram positive
11 Non motile rods
111 Don't produce endospores (non spore forming)
IV Catalase positive
V Non acid fast
VI Are both aerobic and anaerobic but grow best at 30 c in an atmosphere enriched with5 % carbon dioxide for 7-10 days.

The Experiment

Materials and Equipment

1 Pulper
2 Hulling machine
3 Liqouring cups
4 Analytical balance
5 Spoons
6 Electrical kettles
7 Water baths
8 Ph meter
9 Refractors
10 Moisture analyzer
11 Grinder
12 Roaster and gas
13 Thermometers
14 Autoclave
15 Wash bottles
16 Microscopes
17 Air oven
18 Incubators
19 Colony counters
20 Inoculation loops
21 labels
22 Fermentation basins

Glass Ware

1 Beakers
2 Pipettes
3 Conical flasks
4 Petri dish

Chemicals And Reagents

1 Crystal violet
2 Grams iodine
3 95 % alchol
4 Safranine
5 Molten yeast extract lactate (semi solid medium)
6 3 % hydrogen peroxide
7 Peptone water (diluent)
8 Distilled

Coffee Picking

The first ripe coffee berries were selctively picked from the coffee bush ( ripe cherries have adequate mucilage, which is neccessary for pulping, and natural pecteolytic enzymes which degrade mucilage during fermentation)

The harvested cherries were then sorted to remove the immature and dry berries, stones, twigs and food grains which would otherwise be extraneous to the fully ripe cherries.

The cherries were then mechanically pulped, where the red pulp (skin) was removed resulting in parchemnt coffee.

The freshly pulped parchement was graded on the basis of weight and size, by being placed on vibrating sieves, with the coffee flowing at a constant flow. Unpulped cherries and skin were sorted out and directed to the repasser pulper. Heavy parchment was seperated from the light parchment and the two fermented seperately.

Coffee Fermentation

Dry fermentation

(A) The freshly pulped coffee was allowed to ferment while drained of water for 48 hrs, see the table above for the data on fermentation.

After completion of fermentation, the parchment was then washed with clean water and soaked overnight. The parchment was then cleaned and dried on 4/22/95.

(B) The freshly pulped coffee was allowed to ferment for 72 hours, while not under water ( water drained off).

The results of the experiment were tabulated below.

After the completion of the fermentation, the parchment coffee was thoroughly washed with clean water, soaked overnight, rinsed and then dried on the 23rd

Wet Fermentation

The freshly pulped coffee was allowed to ferment while soaked in water for 48 hrs

The Experiment continued here