Coffee and its processing

Coffee Processing

•  Roasting process

It is a time-temperature dependent process, whereby chemical changes are induced by pyrolysis within the coffee beans, together with marked physical changes in their internal structure. The required change takes place with a bean temperature from 190°C upwards; bean temperature up to 240°C may be reached in less than 12 minutes.

Batch operated horizontal rotating drum roaster with either solid or perforated walls, in which hot air from a furnace/burner passes through the tumbling green coffee beans. Green coffee beans under movement are subjected to heat by conduction from hot metal surfaces, or convection from hot air, or more generally a mixture of both methods of heat transfer, together with a contribution by radiation.

A typically sized roaster holds 240 kg of green coffee, with an outturn (charging to discharging) of 15 min. The furnace or burner will be either oil or gas-fired.

Other roasters include:

•       Vertical static drum with blades
•     Vertical rotating bowl
•        Fluidized bed
•        Pressure roasting

The latest roasters have shorter roast times i.e. of the order of 3-5 min. Fast-roasted coffee is advantageous because of lower bulk density and high yield on brewing.

The degree of roast may vary from Very light to very dark.

Consumer preference is usually medium roast.

Physico-chemical changes in coffee

• Chemical Changes 

The chemical changes include Maillard type reactions and caramelization of sucrose. The composition of roasted coffee is furnished below table

The volatile complex comprising of furan derivatives, pyrazines, pyridines, benzenoid aromatics, aliphatics, alicyclic and various sulphur compounds. These are important for the flavour/aroma in medium-roast Arabica coffee.

Some compounds are generated by straight pyrolysis of single compounds e.g. chlorogenic acids in generating phenols; there is an overall 40% residual content for a medium roast. The change in chlorogenic acid content is used as an analytical measure of the degree of roast.

Similarly, coffee oil leads to the formation of small amounts of aldehydes and hydrocarbons. The coffee oil is practically unaffected, as is the caffeine content.

The newly formed residuum of ~ 25% by weight of roasted coffee is melanoidins/humic acids. The loss of mass is 2-3% on a dry basis for Light roast, whereas it is up to 12% on a dry basis for a Very dark roast. The beans lose 15-20% of their weight but increase up to 25% in size.

• Physical changes

The physical changes that occur include:

•        Change in colour.
•        Formation of cavities/cracking of the surface.
•       Void volume is 47% of medium roast bean vs. 0% in the green bean.

• Cooling

In batch operation, the roasted beans have to be quickly discharged at the end of the required roasting period into a cooling car, or vessel, allowing upward passage of cold air.

Also, water may be sprayed from within the rotating drum, just before the end of the roast so-called Water quenching.

Advantages of water quenching

1.   Assists in necessary cooling.
2.  Adds a small percentage of water by weight to roasted beans, thereby assists uniformity of particle size in subsequent grinding.

 Composition of roasted coffee 

Component	Typical average content for (%)
	Arabica	Robusta
Alkaloids (caffeine)	1.3	2.4
Trigonelline (including roasted byproducts)	1.0	0.7
Proteinaceous     Protein      Free amino acids	7.5 0	7.5 0
Lipids (Coffee oil with unsaponifiable)	17.0	11.0
Sugars:     Sucrose     Reducing sugars	0 0.3	0 0.3
Polysaccharides (unchanged from green)	33.0	37.0
Lignin	3.0	3.0
Pectins	2.0	2.0
Acids     Residual chlorogenic     Quinic     Aliphatic	2.5 0.8 1.6	3.8 1.0 1.6
Minerals (oxide ash)	4.5	4.7
Caramelized/condensation products (Melanoidins, etc.)	25.5	25.5
Total	100.0	100.0

 Grinding

Multistage twin horizontal rollers up to 4 stages may be used to ensure more uniform particle size distribution.

1^st and 2^nd stages  Essentially perform cracking or crushing the beans into smaller units.

3^rd and 4^th stages Lead to progressively finer grinding.

The grind size required is related to the subsequent method of brewing to be adopted and whether for home use or subsequent large scale extraction i.e. coarse, medium, fine, very fine. The ground size of roasted and ground coffee beans for different applications is presented below

                                                   Grind size of roasted and ground coffee beans

 

Grind size	Actual size (m)
Fine grind	430 (Europe), 800 (USA)
Coarse grind*	850 (Europe), 1130 (USA)

* for household percolators

The number of different screen sizes numbered by aperture size within the range of 1400 m to 250 m. The newer method performs sizing by laser beams.

Packaging

Roasted and ground (R & G) coffee releases substantial quantities of entrapped CO₂ gas which develops high internal pressure, leading to the bursting of package.

The usual packaging material is laminated.

Packaging under vacuum

It allows a low percentage of oxygen content in the headspace to be established within the package and accommodate the release of CO₂. Alternatively, CO₂ scavenger may be used.

Degas over a sufficient time period

The R & G coffee is allowed in bulk to degas over a sufficient time period to a low level, followed by gas purging whilst individual packages are being filled.

Gas purging is used to ensure that the residual oxygen in the headspace is below 1.0%.

In Europe, the use of plastic packages to which a non-return valve is securely attached allows the release of excess CO_2, when the internal pressure exceeds a certain predetermined level.

A Glance at the Processing Steps

 Green bean treatment

       Cleaning

       Blending

       Storage

   Roasting

 Roast bean treatment

       Storage

       Grinding

       Conditioning

 Extraction

       Fast instant coffee extractors (FIC)

       Conventional batch percolators

       Continuous counter-current extractors (CONTEX)

      FIC extraction unit

It reduces extraction time by 50% compared to batch percolators. Water is directed through the ground coffee in two stages. The process results in two completely separated extract fractions viz., aroma and hydrolysis. After extraction, the extract is filtered and centrifuged.

  Extraction treatment

       Aroma recovery

       Clarification

       Clarification

It is a system consisting of filters and centrifuges to separate insoluble parts from the extract to achieve international standards.

 Concentration

       Falling film and plate evaporators

      Freeze concentration

       Membrane filtration systems

       Concentration: It serves to increase the solids content in extract before freeze or spray drying.

a)      Thermal concentration  Multistage non-recirculating evaporators operating under vacuum in a plug flow model.

b)     Membrane filtration The aroma fraction of the extract can be pre-concentrated using reverse osmosis in a membrane filtration system.

c)      Freeze concentration  By cooling the extract to subzero temperatures, excess water is removed as ice crystals.

Freeze and thermal concentration, membrane filtration, Falling film and plate evaporators are used for the purpose of concentration.

  Drying

       Nozzle Tower spray dryer

       Fluidized bed spray dryer

       Continuous freeze dryers (CONRAD)

       Batch freeze dryers (RAY)

  Agglomeration

       Rewet agglomerators (RWA)

  Packing

  Domestic and Catering Methods of Brewing

Brewing is the extraction of soluble substances contributing to the basic taste plus of volatile substances for overall flavour. Roast coffee must be ground before brewing.

The two main mechanical principles are:

 Steeping/ Slurrying of R & G coffee with water, with or without agitation, followed by sedimentation or filtration or both.

     Percolation in fixed beds of R & G coffee held in an open or closed container. Water may be passed through either in a single pass under gravity or under pressure (including steam, as in Espresso making), or in a multipass.

    Extraction

Extraction of coffee solids can be carried out by

          Fast instant coffee extraction.

          Conventional batch percolators.

         Continuous countercurrent extractors.

  Factors in Brewing

          Coffee-to-water weight ratio

          The appliance used for brewing.

          The temperature employed.

Of the components of roasted coffee, only some will be extracted completely with variable amounts of the others to reach ~ 28% w/w total maximum and 21% optimum under household brewing conditions, by hot or boiling water so-called yield.

The mechanical operation involved is a means of separating the undesired so-called Spent coffee grounds from the required brew formed by sufficient contact with water. The brew should contain as little of spent ground particles as possible and must be presented hot (i.e. 50-55°C).

  Flavour Quality of Coffee Brew

The factors determining the flavour quality of brew include:

       The choice of blend used.

       The degree of roast.

       Brewing conditions.

       Choice of grind.

 Filter coffee

South Indian Coffee, also known as Filter Coffee is a sweet milky coffee made from dark roasted coffee beans (70-80%) and chicory (20-30%), especially popular in the southern states of Tamil Nadu and Karnataka. The most commonly used coffee beans are Arabica and Robusta.

Outside India, a coffee drink prepared using a filter may be known as Filter Coffee or as Drip Coffee as the water passes through the grounds solely by gravity and not under pressure or in longer-term contact.

 Aromatization of Coffee

It is a term applied to a process, whereby essentially the headspace coffee aroma volatiles are made available by plating coffee aroma oil, prepared by expression methods from roast coffee, or other sources onto the soluble coffee, usually at the packing stage. This is a treatment imparted to improve the flavour and aroma. The powder lacks full flavour and aroma of freshly brewed coffee. The flavour and aroma constituents are trapped and recovered during roasting, grinding and extraction and from oils pressed from the coffee bean. The cold CO₂ does not damage the flavour and aroma compounds in coffee oil and it is easily separated from extracted oil for recompression and reuse.

After CO₂ removal of the oil, the Roasted and Ground coffee is still highly suitable for extraction of water-soluble solids in the regular extraction battery operation.

 Aroma recovery

The extract fractions are stripped of their volatiles in an aroma recovery unit. After being stripped from the concentrate in a flash evaporator, the aroma is recovered in a 2-stage condenser system. 

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Processing of butter - How it is made?

Butter- 

Fat separated from the cream 

1. Butter may be defined as a fat concentrate which is obtained by churning cream gathering the cat into a compact mass and then working on it.
2. According to PFA rule, there are certain specification for butter, 

• It should be free of animal fat, wax, mineral oil and vegetable oil. 
• There should be no preservative except salt (NaCl).
• Should not contain less than 80% fat.
• Not more than 1.5% curd. 
• Also NaCl not be used more than 3%.
• Diacetyl may be added but not more than 4 ppm, which gives the typical flavour. 
• In butter, some of the alkalines are added - Calcium Hydroxide, Sodium Bicarbonate.  

Various kind of butter -

1. Pasteurize cream butter
2. Ripened cream butter
3. Unripened cream butter
4. Salted butter
5. Unsalted butter
6. Sweet cream butter
7. Sour cream butter
8. Fresh butter
9. Cold storage butter
10. Dairy butter
11. Creamy butter

The standard composition of butter 

Butterfat - 80.2%

Moisture - 16.3%

Salt - 2.5%

Curd - 1% 

Fat-soluble vitamins - Vit- A, D & K

Method of Manufacturing 

Important points- 

1. Grading of cream based on the quality of cream- 

• 1-grade cream is sweet cream and slightly sour.
• 2-grade cream is sour and coagulated. 
• 3-grade cream is rejected, quite fermented.

    2. Testing - cream is tested for fat, SNF and acidity. 

    3. Preheating - to increase the efficiency of the operation. 

    4. Ripening - Addition of starter culture for fermentation, to enhance the flavour and lesser fat loss in the serum. It is ripened by the starter culture that is streptococcus lactis and Streptococcus cremoris. Some more microorganisms are known as aroma producer- 

• Streptococcus diacetylactis
• Leuconostoc citrovorum
• Leuconostoc dextranium

1. These microorganisms produce diacetyl which gives the typical aroma.
2. Inoculated at 21°C for 15-16 hours.
3. Acetic acid or propionic acid also gives some flavour.
4. Set range for standard diacetyl content is 0.2 to 0.6 ppm gives a mild flavour to butter.
5. More than 2.55 ppm and 4 ppm rise in butter could be rejected. 
6. Mother substance from which diacetyl is produced are acetyl, methyl and sometimes citric acid is added before fermentation.  

Churning - 

Separation of fat from cream. Agitation of cream at a suitable temperature until the fat globule adheres to forming a larger and larger masses until the complete separation of fat and serum occur.

• Cream in a form of emulsion - stable in nature
• fat - skim milk emulsion 
• churning breaking out the stability of fat and milk 

Force for making stable

Surface Tension - 

- Cream and fat globule retain their individuality

- Prevent butter formation 

Phenomena of adsorption - 

- Fat globule in milk or cream, they are in a layer which is phospholipid layer. 

- This membrane resists de - emulsification 

- Adsorb at the surface of fat globule

- They make the charge stabilize. 

Electric Charge - 

- Fat globules are negatively charged. 

- result all of them repel each other.

Viscosity - 

- higher the viscosity more stable is an emulsion 

- Resist Churning 

During the churning, the temperature is above the melting point of the fat 31-38°C. Agitation results in the subdivision of fat and serum.

Churning operation - 

1. It starts with the preparing of churning by cleaning, sanitization and deals with all the types of pre-treatment.
2. Filling cream into the churn, slightly above the capacity. 
3. Addition of butter colour- carotene and annatto, 250 ml of colour is added to 100 kg of butter. 
4. Operation of churning - 

• Initial rotation (5-10 times)
• liberate any gas present in the cream. 
• the rise in temperature of 1-3 °C of the cream
• Foaming
• addition of water to lower the temperature
• after the foaming, breaking stage occurs when the cream breaks away, the formation of butter grains of pea-size.
• Churning is stooped and fat is collected
• washing of butter - to remove every adhering particle of serum or buttermilk.

The procedure of washing - 

Buttermilk is drained, then water is added to butter which has the temperature 1-2 °C lower than churned butter, the amount is equal to the amount of buttermilk separated from fat. Then churned is again switched on after few rotations then water is drained out. Washing is followed by salting and working (kneading of butter)

Reason for adding salt - 

• To improve the keeping quality 
• to enhance the taste 
• to increase the overrun 
• Salt must not be exceeded to 2-2.5%, maximum 3%. 

The objective of kneading or working - 

1. To complete dissolve, uniformly distribution and properly incorporate the salt. 
   To expel the buttermilk and to control the moisture content of the butter.
2. To bring the butter raise together into the compact mass, convenient to handling and packaging.

Packaging of butter - 

Packaging material for butter should have excellent barrier properties such as

· It should be moisture-proof

· It should be greaseproof

· It should be impervious to light

· It should have good strength (to prevent tampering during transportation etc.).

Some of the packaging materials used for butter packaging are

i) Parchment paper – also known as butter paper.

ii) wax-coated paper

iii) cellophane

iv) cardboard boxes and teak wood drums lined with food-grade plastic

v) Aluminium foil laminates

vi) Lacquered tin cans (it is costly but is advantageous in tropical countries and prevents de-shaping during storage and transportation.)

Techniques of packaging

1. Manual moulding and wrapping

2. Mechanical moulding and hand wrapping

3. Fully automatic units which mechanically moulds, patts and wraps. It reduces labour cost, handling losses and is suitable for large scale operation. The machine can be reset for different size viz. 10, 15, 100, 250 and 500g. Some of the well-known brands of fully automatic butter packaging machines are Kustner, Benhill (both are German) and SIG (Swiss). In these machines, after wrapping, the pat goes to carton machine for packing in card boxes and transferred to cold storages (5°C) for 24-48 h and then shifted to low-temperature storage (-23 to -29°C).

Storage of Butter

For the sake of consistency and appearance, butter should be placed in cold store as soon as possible after wrapping and should be chilled to 4°C for 24 to 48 h. Unless this is done, fat crystallization is very gradual and the butter retains its freshly churned consistency and appearance for several days. However, once it has been sufficiently chilled, a subsequent rise in temperature will not make it as soft as it would have been at the same temperature prior to its chilling. The initial freshly churned, somewhat ointment like consistency is transformed to that typical for butter. This change is known as the setting of butter. The butter cannot be considered finished until it has been chilled or set. A low storage temperature also improves its keeping quality and reduces the risk of the package being deformed.

As butter is essentially a perishable product it should not be stored longer than necessary. However, when production exceeds demand and also quite often to level out the fluctuation between high flush season production and low summer production, storage of butter becomes unavoidable. For a short period, butter can be stored at about 4°C but if longer storage is involved it must be deep-frozen at -23°C and only best quality butter should be selected for deep freezing. Since the solubility of salt is low (35.7% at 0°C), some salt crystallization may occur during storage but the crystals re-dissolve on thawing.

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Pasteurization

Pasteurization 

Pasteurization is a relatively mild heat treatment, in which food is heated to below 100ºC. In low acid foods (pH > 4.5, for example, milk) it is used to minimise possible health hazards from pathogenic micro-organisms and to extend the shelf life of foods for several days. In acidic foods (pH 4.5, for example, bottled fruit) it is used to extend the shelf life for several months by the destruction of spoilage micro-organisms (yeasts or moulds) and/or enzyme inactivation. In both types of food, minimal changes are caused to sensory characteristics or nutritive value. Processing containers of food, either which have a naturally low pH (for example fruit pieces) or in which the pH is artificially lowered (for example pickles) is similar to canning. It is often termed pasteurization to indicate the mild heat treatment employed.

The process was named after the French microbiologist, Louis Pasteur, whose research in the 1880s demonstrated that thermal processing would inactivate unwanted microorganisms in wine. Spoilage enzymes are also inactivated during pasteurization. Today, pasteurization is used widely in the dairy industry and other food processing industries to achieve food preservation and food safety.

Purpose of pasteurisation for different foods

 Pasteurization process

Pasteurization is a mild heat treatment of liquid foods (both packaged and unpackaged) where products are typically heated to below 100 °C. The heat treatment and cooling process are designed to inhibit a phase change of the product. The acidity of the food determines the parameters (time and temperature) of the heat treatment as well as the duration of shelf life. Parameters also take into account nutritional and sensory qualities that are sensitive to heat.

Equipments-

Food can be pasteurized in two ways: either before or after being packaged into containers.

Batch method

The batch method uses a vat pasteurizer which consists of a jacketed vat surrounded by either circulating water with added steam or heating coils of hot water or direct steam. In the vat the milk is heated and held throughout the holding period while being agitated. The milk may be cooled in the vat or removed hot after the holding time is completed for every particle. As a modification, the milk may be partially heated in tubular or plate heater before entering the vat. This method has very little use for milk but some use for milk by-products (e.g. creams, chocolate) and special batches. The vat pasteurizer is used extensively in the ice cream industry as it allows for dissolution and blending of ingredients during the heating stage.

Continuous Method

Continuous process method has several advantages over the vat method, the most important being time and energy saving. For most continuous processing, a high temperature short time (HTST) pasteurizer is used. The heat treatment is accomplished using a plate heat exchanger. This piece of equipment consists of a stack of corrugated stainless steel plates clamped together in a frame. There are several flow patterns that can be used. Gaskets are used to define the boundaries of the channels and to prevent leakage. The heating medium can be vacuum steam or hot water.

Temperature	Time	Pasteurization Type
63ºC (145ºF)*	30 minutes	Vat Pasteurization
72ºC (161ºF)*	15 seconds	High temperature short time Pasteurization (HTST)
89ºC (191ºF)	1.0 second	Higher-Heat Shorter Time (HHST)
90ºC (194ºF)	0.5 seconds	Higher-Heat Shorter Time (HHST)
94ºC (201ºF)	0.1 seconds	Higher-Heat Shorter Time (HHST)
96ºC (204ºF)	0.05 seconds	Higher-Heat Shorter Time (HHST)
100ºC (212ºF)	0.01seconds	Higher-Heat Shorter Time (HHST)
138ºC (280ºF)	2.0 seconds	Ultra Pasteurization (UP)

Effect on foods

Pasteurisation is a relatively mild heat treatment and even when combined with other unit operations there are only minor changes to the nutritional and sensory characteristics of most foods. However, the shelf life of pasteurised foods is usually only extended by a few days or weeks compared with many months with the more severe heat sterilisation. Minimising postprocessing contamination is essential to ensure adequate shelf life.

Colour, flavour and aroma

In fruit juices, the main cause of colour deterioration is enzymic browning by polyphenol oxidase. This is promoted by the presence of oxygen, and fruit juices are therefore routinely deaerated prior to pasteurisation. The difference between the whiteness of raw milk and that of pasteurised milk is due to homogenisation, and pasteurisation alone has no measurable effect. Other pigments in plant and animal products are also mostly unaffected by pasteurisation. A small loss of volatile aroma compounds during pasteurisation of juices causes a reduction in quality and may also unmask other ‘cooked’ flavours. Volatile recovery may be used to produce high-quality juices but this is not routinely used, due to the high cost. Loss of volatiles from raw milk removes a hay-like aroma and produces a blander product.

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