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PART 1 OVERVIEW OF COFFEE AND COFFEE PROCESSING TECHNOLOGY This is a form of granulation, which is the process of turning particles into smaller particles by the breaking force greater than the cohesi[.]
PART 1:OVERVIEW OF COFFEE AND COFFEE PROCESSING TECHNOLOGY This is a form of granulation, which is the process of turning particles into smaller particles by the breaking force greater than the cohesive force of the crushed powder particles There are different types of grinding: - The process of turning solid raw materials into small particles of definite size These particles are the end products of the grinding process This method of grinding is called simple grinding It gives high productivity, often used for shaft crushing equipment - Complex crushing is the process of turning solid materials into smaller particles, but after each crushing, classified and particles of different sizes are put into different grinding systems for further grinding Crushing equipment has a complex struFormulaure, low productivity but uniformly ground powder Depending on the material properties such as size, hardness, viscosity, oil content in seeds and technological requirements of the product after grinding, the size of the crushed powder corresponds to a high ratio, uniformity, and yield , energy costs etc have suitable grinding cycles - Closed cycle: Raw materials are fed direFormulaly into the crusher Powder product out of the machine, into the sorting device The number of products that meet the requirements through the sorting device, the products that not pass continue through the crusher with new materials This cycle has low economic efficiency, is rarely used due to low productivity, high energy costs, even though the powder is ground evenly - Dual cycle: Raw materials of various sizes pass through a sieve to make the general size uniform before entering the crusher and colleFormula the product after leaving the crusher This cycle has high productivity, so it is widely used in today's coffee grinders The product is powdered coffee, after roasting and impregnating the coffee, it is ground instead of packing The fineness of the ground powder greatly affeFormulas the extraFormulaion process and the time when boiling water is absorbed through the coffee powder (coffee making time) The higher the fine particle distribution, the faster the coffee processing time with high accuracy (MPE document _ USA) The temperature of the coffee powder should be 30-400C to keep the coffee flavor The fine brown powder was analyzed through a sieve with diameters (mm) respeFormulaively 0,5 0,30,20,150,1250,097 to determine the following fine particle distribution % squish The proportion of ground coffee is 4-5% The water solubility is 25-35% Ash content 5% and insoluble ash 0.1% Caffeine content - 1.4% Impurities < 5mg/1kg Powdered coffee can be stored for up to 1-3 months If longer storage is required, vacuum packaging or inert gas packaging is required Caffeine in coffee is a substance that affeFormulas health, there are methods to separate caffeine: - Separation with organic solvents methylene chloride, dichloromethane - Water separation gives higher extraFormulaion rate and more pure caffeine is obtained The coffee is passed through the extraFormulaion column and the water flows for hours The caffeine extraFormulaion efficiency is 98%, the decaffeinated coffee has 53% moisture and is dried and processed normally *Preminilary about heat during the grinding process : Friction created during the grinding process generates some amount of heat Usually, the commonly given visual explanation for this is that the metal parts of the blender expand at higher temperatures, increasing the distance between the burrs and letting in larger-than-installed particles put This is not entirely true, however, as the expected expansion of the metal for such a small temperature change would be negligible High temperatures during grinding can also accelerate degassing and oxidation, which can result in a great loss of aroma Typically, the reason grinders overheat is because they have been operating for too long or grinding too much coffee in a short period of time But it could also be because too much coffee has been poured into the hopper or the environment in which the grinder is operating is too hot – for example, in coffee roasteries PART 2: GRINDING EQUIPMENT OVERVIEW 2.1 Overview Grinding equipment is one of the important factors affeFormulaing the quality of coffee powder It ensures production productivity to meet the needs of products for domestic consumption and export In the process of crushing raw materials, the grinding groove, the grinding surface is always subjeFormulaed to harsh conditions such as temperature, abrasion, compression pressure, vibration, impact Depending on the raw material conditions such as moisture, oil content, material size, etc., the groove profile, grinding surface and kinematic parameters are suitable to increase the quality of ground powder and ensure productivity and the durability of the grinding mechanism with long or short service life The grinding mechanisms are made of materials with hardness, wear resistance and heat resistance 2.2 Theoretical basis of crushing: Raw materials from large lumps or granules through the process of grinding into lumps, smaller particles or coarse, medium, and fine powder Let's call the average size of the finished product after grinding before grinding is D and the average size of the finished product after grinding is d 2.2.1 Table of crushing level of raw materials: Crushing level Dimensions (mm) D d 1000 – 200 250 – 40 Medium 250 – 50 40 – 10 Small 50 – 25 10 – 5–1 0,1 – 0,04 0,2 – 0,04 0,015 – 0,005 Squish Rough Powder grinding Large Medium Fine 0,1 – 0,04 0,005 – 0,001 Ultrafine 0,1 – 0,04 0,001 2.2.2 Grinding methods: The process of crushing materials by means of mechanical forces Types of mechanical aFormulaion to break down materials to be crushed Depending on the struFormulaure of the mill, there are forces to break the material such as: compressing, pressing, splitting, breaking, cutting, sawing, sliding, smashing to create many smaller samples of materials Depending on the nature of the crushed material, appropriate breaking forces are required: - Compression force is suitable for brittle, soft, medium, very hard material struFormulaure The energy expended for this process is elastic deformation and breaking of the material - Cutting force, slitting and rubbing is easy for soft materials, but limited rubbing is suitable for brittle, medium hard materials All of the above forces are used in the coarse grinding method If you want to grind smaller, increase the friction between the grinding surfaces and the crushed material Table 2.2: Table of adaptive force classification for each grinding material: Force Crush Compress Rub Collide Very hard Suitable Suitable Medium hard Suitable Suitable Limited Suitable Soft Limited Suitable Suitable Suitable Crispy Suitable Suitable Limited Suitable Cut Ingredient Suitable Table 2.3: Comparison of crushing, number of particles after grinding/gram (shaft mill, Department of Machine Building, HCM City University of Science and Technology) Particle charaFormulaeristic Grain size d after grinding (mm) Number grinding/g of particles after s Even size 1,0 1296 Medium 0,75 3072 Smooth 0,38 24572 Average size (mm) of coffee beans (7-10) x (4-7) x (3-5) - The average volume of an coffee bean is 187mm3 So that the size of cube of the ground types as raw, semi-fine and fine coffee is as follows: - Coarse grinding has 100-300 pieces/grain the average volume of a sample after coarse grinding: 187 x 0,395mm (1x1x1) mm 100 300 - The volume of coarsely ground powder sample increased (100÷300) times Coarse, semi-coarse and fine mills require limited rubbing of the material between the two mill faces (a pair of shafts with a ring speed ratio) to give a fine particle distribution of the ground powder - Semi-fine grinding with 500-800 samples/grain Average volume of a sample after semi-fine grinding: 187 x 0,2877 mm (0,66 x 0,66 x0,66)mm 500 800 And the volume of semi-fine powder sample increased by 800/300÷500/100 = (2.66÷5) times - Fine grinding with 1000-3000 samples/grain: -Average volume of a sample after fine grinding: 187 x 0,0935mm (0,4539 x0,4539 x0,4539)mm 1000 3000 And the volume of finely ground powder increases: 1000/500÷3000/800 =(2÷3.75) times Comment: - The number of times of new samples after semi-fine grinding is greater than that of fine grinding - The average size of each type of crushed sample is as follows: Coarse mm Semi-fine 0.66 mm Fine 0.4539 mm 2.2.3 Crushing theories (approximate statements and formulas): a) P.R Rittingo's Surface Theory (A = fD2) The work for the grinding process is proportional to the newly formed surface of the material to be ground Bees hypothesized that the material to be ground would have a cube shape Work: A = 6ArD2(i – 1) Ar: specific work done when grinding to create a new surface unit D is the original cube size and d is the cube size after grinding i =D/d In faFormula, the raw materials before grinding and after grinding have any shape On the other hand, work is not only used to destroy the material to create a new surface, but also to deform the material before breaking Therefore, when calculating, the correFormulaion factor k must be added so so A = 6kArD2(i – 1).k = 1.2 1.7 (depending on shape, material properties and grinding method) Conclusion: the grinding process is very complicated b) Kieppitrov's volume theory: The work consumed for grinding is proportional to the volume of the deformed part of the body The basis of volume theory is the calculation of the work done to deform an objeFormula when it is crushed The work consumed for grinding is proportional to the volume of the deformed part of the body The basis of volume theory is the calculation of the work done to deform an objeFormula when it is crushed A= Pd , with Pl EF E : elastic modulus F: deformed area P At that time: A = Pl P l 2 dP V EF 2EF 2E : compressive stress in deformation; P F V : volume of the deformed objeFormula; V = lF Two bodies of the same material, which are similar to each other before an external force is applied to them, will remain similar to each other after impact, if the forces are uniformly distributed along the surfaces of both bodies, and the magnitudes of the respeFormulaive forces per unit area are the same in both bodies Corresponding to the above law, the particles of the objeFormula that are crushed under certain conditions are geometrically similar to each other If it is not enough to obtain the predefined knowledge by crushing once, it must be repeated a number of times into smaller and geometrically similar particles Since the crushing volume remains constant, the energy consumed for crushing with each break is the same if the grinding mode Z is fixed x : number of times of crushing the cube-shaped objeFormula, reducing the size from L to l n : number of particles formed after each grinding, due to each particle in the previous crushing break L3 Z3 l3 : the number of particles of the final break into which each element initially broke lg Z Infer: nx = Z3 x = lg n If A' is a fixed energy consumption for each crushing of the volume of the objeFormula, the work to grind to a predetermined size l will be equal to: lg Z Ak = A’.x = A’ lg n = KK.lgZ So the crushing work is proportional to lg of the crushing Z c)Rebinder's synthesis formula: General formula for crushing objeFormulas: A = f1(V) + f2(S) = AV + AS = kV + S AV : plus consumption for the deformation (elastic) volume fraFormulaion V of the objeFormula AS : work consumed for newly formed areas S of the objeFormula k : scale factors Rebinder explains that the volume theory energy is less close to the experimental results because when crushed, on the surface of the objeFormula, at first, many small cracks are formed on the surface of the body called "the region about to be crushed" When the external force is no longer acting, the cracks in that region can be closed due to the aFormulaion of the attraFormulaion force linking the particles of the objeFormula Therefore, the term S is the work consumed to produce the area summed up by the newly formed area Sm and the area of the closed cracks Sk, that is: S = (Sm + Sk) The AS work that creates new areas is useful, while the elastically deformed AV work is useless Therefore, it can be considered that the efficiency of the crushing process is the lowest and equal to AS AS AF The above work formulas of the three crushing theories applied in aFormulaual production are theoretical formulas It is experimentally correFormulaed for each type of grinding material Through the aFormulaual production of imported coffee grinders, it did not match the K (mechanical properties) of the roasted coffee beans in our country Therefore, an efficient grinding process cannot be performed Therefore, in order to have an effeFormulaive grinding process, it is required that the profile of the axes acting on the impregnated coffee beans creates many new surfaces and new textures after grinding and to overcome the pulverized powder into the groove, it is necessary to increase the crushing ability, crush, break, impact and limit the possibility of rubbing (or with the help of a cleaning mechanism) 2.3 Analysis and seleFormulaion of options for coffee grinders Figure 2.1 - StruFormulaure: Consists of steel mill shafts rotating in opposite directions The shaft of the grinding drum (2) is placed on a movable bearing which is always held in place by a spring (3) - Classification: - Type with fixed grinding drums: this type has two grinding drums that cannot move, so when rolling with solid materials, it is easy to damage the grinding drum So this machine is only used for crushing soft materials - Type movable shafts: the shafts of grinding drums have teeth When crushing, if the material is too hard to crush, the spring (3) is compressed, the gap between the two shafts widens, the material will fall, then the spring pushes the shaft back to its original position The typical basic dimensions of the shaft mill are the drum diameter D and the length L The ratio of the length to the shaft diameter L/D = 0.5 – 2.5 On the shaft surface smooth or rough If the medium hardness material is crushed, the knurled shaft is made The shaft mill has a crushing capacity of 10 - 15 The rotation speed of the two grinding shafts can be the same, or they can be different When the two shafts rotate at different speeds, the crushing process is enhanced Advantages: Simple struFormulaure, solid, reliable work, less noise and dust The lower the shaft speed, the less heat is generated and therefore less moisture is lost in the material The resulting particles are more uniform in size, very little crumbs are formed With the same particle size, mass Disadvantages: - The material after crushing or flattening, is not suitable for grinding high hardness materials, has a poor effeFormula on fibrous materials - High initial investment, high maintenance cost The parallelism between the grinding shafts needs to be ensured, so an effeFormulaive clearance adjustment mechanism is needed Shaft crusher is often used to crush materials with low strength to avoid damage to the shaft and increase the use time Even so, the shaft mill is still widely used in the food processing industry 2.4 Design plan of shaft crusher 2.4.1 Axis layout plans Figure 2.2 Axis layout plans - Figure a: is a machine with fixed shaft bearings, this type has a simple struFormulaure but works unsafely when the gap between the two shafts has hard objeFormulas in or when the machine is overloaded Only used for grinding flexible materials… - Figure b: is a machine with a fixed shaft, a shaft with a movable pillow that is held by a spring, so when rolling a hard material it will push the roll back and fall Therefore the rolling shaft is not damaged This type is commonly used