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The perfect coffee .
That is, to extract and put into solution , the coffee oils and the soluble (and semi-soluble compounds) that are formed when the coffee bean is roasted.18%-22% is the optimum extraction rate for good coffee.
Under Extraction occurs when the brewing time is too short and not enough coffee soluble are extracted into solution. This can occur if the water is not hot enough or if the water passes through the ground coffee too quickly. An insipid, thin brew lacking in body and flavour will result .
Over Extraction occurs when the water is in contact with the ground coffee for too long and too much of the coffee soluble are extracted than is desirable. A harsh tasting bitter brew will result.
Freshness – Coffee is best enjoyed as soon as it has been brewed. Oxygen in the atmosphere causes the taste to rapidly deteriorate and the beverage loses its aromatic oils and may soon become sour , flat and lifeless. Freshly brewed coffee should be consumed within 30 minutes if left on a hotplate and should never be reheated.
The quality of the brewed coffee beverage will depend on several factors, all of which are important to produce the perfect cup of coffee:
1) Grind size of the coffee
2) Quantity of coffee used
3) Water quality
4) Water temperature
5) Contact (infusion) time
6) Type of brewing method used
7) Hygiene and cleaning practices
* Grind size:
Over-extraction can occur if the grind is too fine for a particular brewing method and under-extraction can occur if the grind is too large. The important thing here is the brewing method used, as different methods require different infusion times and consequently a different grind size.
Clearly coffee brewed in a simple coffee pot where hot water is merely added to the ground coffee in a pot a coarse grind should be used as the hot water is likely to be in contact with the coffee for a long time.
Inversely in an espresso machine the water is only in contact with the grind for 20-25 seconds ( although under pressure) so a very fine (or espresso) grind is needed for optimum flavour extraction to occur.
In a similar vein drip filter coffee machines require a medium to fine grind as the filter paper restricts the flow of hot water into the jug but even so the infusion time is quite short.
The cafetiere (or French Press) method requires a medium grind as the coffee may infuse for a while before the customer decides to end the infusion process by depressing the integral strainer to trap the used grounds at the bottom of the pot.
* Quantity of coffee used:
It is imperative to use the correct amount of coffee appropriate to the equipment used to brew it.Using less coffee than recommended by compensating by using a longer brew time will not result in a standard brew but just produce an over-extracted beverage. By the same token using more coffee than recommended and using a quicker infusion time will just result in an under-extracted coffee.
Approximate measures:
1 ounce of coffee to 1 pint of water
60 grams of coffee to 1 litre of water
¼ ounce of espresso grind for a typical espresso
8 grams of espresso grind for a typical espresso
1 heaped teaspoon = 2.5 grams of coffee
1 rounded tablespoon = 7.5 grams of coffee
4-5 tablespoons of coffee for 1 pint of water
* Water quality
In a good cup of coffee approximately 98.5% of the beverage is water.
Steep and Strain – The simplest method of all. Hot water (just off the boil ) is added to coarse to medium ground coffee in a container and the mixture left to ensure extraction (steeping). The coffee liquor is strained off or the steeping halted in some mechanical way prior to serving. This methods is best suited to domestic or light commercial use.
Examples include the coffee jug, percolator, French Press, Ibrik
Filter Infusion – Medium to fine ground coffee are placed in a basket or container which is lined with a filter paper or other material designed to let the hot coffee liquor slowly filter through to a holding pot or container.
Hot water is a added from above it steeps with the coffee grinds in the basket and falls through into the container below.
This method is suitable to both domestic and commercial use. Examples include, drip and filter pots, pour and serve machines and commercial bulk brewers.
Pressure Infusion – Hot water if forced under pressure through a small compacted bed of finely ground coffee held inside a small metal basket. This is known as the espresso process and is generally suited to preparing individual cups of beverage rather than a jug or container.
* Hygiene:
All parts of coffee brewing equipment should be regularly cleaned and sanitised and areas that come into contact with the beverage kept clean .In addition the coffee beans or ground coffee should be kept fresh in air tight containers away from damp areas and out of direct sunlight.Coffee beans contain a high percentage of oils and the residue on un-cleaned equipment can quickly form black sticky tars which can easily contaminate the next brew. All coffee brewing equipment and surrounding areas should be washed down with hot water containing a mild detergent and thoroughly rinsed.To produce great tasting coffee is is crucial to have clean brewing equipment.