Etiket Arşivleri: Moisture Content
Dryer – is an equipment used in removing moisture or solvents from a wet material or product.
Hygroscopic Substance – a substance that can contained bound moisture and is variable in moisture content which they posses at different times.
Weight of Moisture – amount of moisture present in the product at the start or at the end of the drying operation.
Bone Dry Weight – it is the final constant weight reached by a hygroscopic material when it is completely dried out. It is the weight of the product without the presence of moisture.
Gross Weight – it is the sum of the bone-dry weight of the product and the weight of moisture.
Moisture Content – it is the amount of moisture expressed as a percentage of the gross weight or the bone dry weight of the product.
A) Wet Basis – is the moisture content of the product in percent of the gross weight.
B) Dry Basis 0r Regain – it is the moisture content of the product in percent of the bone dry weight.
Continuous Drying – is that type of drying operation in which the material to be dried is fed to and discharge from the dryer continuously.
Batch Drying – is that type of drying operation in which the material to be dried is done in batches at definite interval of time.
CLASSIFICATION OF DRYERS
1. Direct Dryers – conduction heat transfer
2. Indirect Dryers – convection heat transfer
3. Infra-red Dryers – radiation heat transfer
1. GW = BDW + M
2. Xm = [M/GW] x 100% (wet basis)
3. Xm = [M/BDW] x 100% (dry basis or regain)
GW – gross weight
BDW – bone dry weight
M – weight of moisture
Xm – moisture content
HEAT REQUIREMENT BY THE PRODUCT
Q = Q1 + Q2 + Q3 + Q4
Q1 = (BDW)Cp(tB – tA) kg/hr
Q2 = MBCpw(tB – tA) kg/hr
Q2 = MB(hfB – hfA) kg/hr
Q3 = (MA – MB)(hvB – hfA) kg/hr = MR(hvB – hfA)
Q4 = heat loss
Q1 – sensible heat of product, KJ/hr
Q2 – sensible heat of moisture remaining in the product, KJ/hr
Q3 – heat required to evaporate and superheat moisture removed from
the product in KJ/hr
Q4 – heat losses, KJ/hr
A,B – conditions at the start or at the end of drying operation
t – temperature in C
hf – enthalpy of water at saturated liquid, KJ/kg
hv – enthalpy of vapor, KJ/kg
Cp – specific heat of the product, KJ/kg-C or KJkg-K
Cpw – specific heat of water, KJ/kg-C or KJ/kg-K
FE 272 FOOD CHEMISTRY LAB Experiment 1
DETERMİNATİON OF MOISTURE CONTENT
Name of Experiment : DETERMINATION OF MOISTURE CONTENT
Number of Experiment : 1
Submitted by : Kenan ÖZ
Define the moisture content.
The determination of moisture is one of the most important and widely used analytical measurements in the processing and testing of food products.
The moisture content is frequently an index of stability and quality, and is also a measure of yield and quantity of food solids. It is closely concerned with the economics and legal aspects of food processing.
The moisture content of foods varies considerably: for fresh fruits, from 65% in ripe avocados to 95% in rhubarb; for fresh vegetables, from 66% in green beans to 96% in cucumbers; for fresh meat and fish, from 50 – 75%. The moisture content of processed foods varies even more from about 7 – 12% for dried vegetables to 27 -35% for jams and jellies.
What is the relationship between water activity and moisture content?
Water activity is an important means of predicting and controlling the shelf life of food products. Shelf life is the time during which a product will remain safe, maintain desired sensory, chemical, physical and microbiological properties, and comply with nutritional labeling.
The relationship between moisture content and water activity is complex. An increase in aw is almost always accompanied by an increase in the moisture content, but in a nonlinear fashion. This relationship between water activity and moisture content at a given temperature is called the moisture sorption isotherm. These curves are determined experimentally. Moisture sorption isotherms are sigmoidal in shape for most foods, although foods that contain large amounts of sugar or small soluble molecules have a J-type isotherm curve shape. A moisture sorption isotherm prepared by adsorption (starting from the dry state) will not necessarily be the same as an isotherm prepared by desorption (starting from the wet state). This phenomenon of different aw vs. moisture values by the two methods is called moisture sorption hysteresis and is exhibited by many foods. Many disciplines use water content calculations to regulate product quality, however, water content measurement can be inaccurate, time-consuming and require a precision balance.
Write the importance of monolayer value for the foodstuffs.
The importance of monolayer value for the foodstuffs is physically bound as monolayer the surface of the food constituents.
What are the advantages and disadvantages of each methods (drying, distillation, chemical and instrumental methods)?
Advantages: Different temperature of drying may result in a different amount of free water loss, so it is important to compare results obtained using the same condition.
Disadvantages: Weight lost, volatile oils may be lost.
Advantages: It has advantages of needing little attention and do not separate with the water and so are not measured.
Chapter 5. Determination of moisture
Section 1. General
Moisture determiantion is one of important and most widely used measurements in the processing and testing of foods.
Stability and quality of foods
1. Water forms
2. Methods of moisture determination
Direct determinantion: remove the moisture in sample by the methods of drying, distillation and extration.
Indirect detremiantion: using sample’s density, refraction, conductivity or capacitance to measure the moisture content.
Direct determination: good accuracy and repetition, but spending long time.
Indirect determination: fast and automatic, but slightly week on accuracy .
Section 2. Determination of moisture
1. Drying methods
The procedures for determination the moisture content specified in food standards generally involve thermal drying methods.
The material is heated under carefully specified conditions and the loss of weight is taken as a measure of the moiture content of the sample.
Drying methods are:
Simultaneous analyses of large numbers of samples
Preconditions of drying methods
Water is the only volatile material.
Water can be removed drastically.
During heating, weight loss caused by chemical reactions in other components can be ignored.
1.1 Directly drying method
Principle: In certain tempatature (95-105℃) and pressure, samples are heated in oven and then water in samples is vaporized. The loss of weight is moisture content of samples.
Applying range: There is no other volatile materials besides water. furthermore, the sample is stable when heating.
DETERMINATION OF MOISTURE CONTENT THEORY
The moisture content influences the physical properties of a substance such as weight, density, viscosity, refractive index, electrical conductivity and many more. Chemical, thermogravimetric or loss on drying techniques are used to determine this content.
Why measuring moisture ?
Most natural products contain moisture. The water content per se is seldom of interest. Rather, it shows whether a product intended for trade and production has standard properties such as
– Agglomeration in the case of powders
– Microbiolgical stability
– Flow properties, viscosity
– Dry substance content
– Concentration or purity
– Commercial grade (compliance with quality agreements)
– Nutritional value of the product
– Legal conformity (statutory regulations governing food)
There are several moisture determination methods such as
− Moisture determination with Karl Fischer titration
− Moisture determination by thermogravimetric method
− Moisture determination by drying-oven method
− Moisture determination with halogen moisture analyzers
Tray dryers and their developed forms, tunnel dryers are equipments, which found many applications in food operation operations during dehydration of foods. All the drying characteristics of foods can be observed in these equipments. A typical drying procedure was applied with tray dryer to investigate properties of tray dryers, its advantages or disadvantages, drying kinetics of foods that are dried in tray dryers.
For these purposes, equilibrium moisture content, drying rate, mathematical and experimental drying time were calculated with some engineering formulas. Wet pepper was used as sample The result demonstrated that the most important parameters in drying of foods by tray dryer, which affect the time and the quality of food, are temperature and velocity of air, moisture content of food and surface area that is exposed to heated air.
In this experiment we produced malt to produce beer.The main operation is the germination of barley.This operation activates and produces enzymes.We know, m/o’s produce alcohol from simple sugars.The enzymes which are activated during germination convert starch of barley to simple sugars (These enzymes are hydrolitic enzymes.).Also thet effect flavor and foam formation.Germination step is started with soaking to increase the moisture content about 40-45%.When germinated barley was dried , green malt is produced.This determines the type of beer.Low temperature dried malts is the raw material for pilsner type beer, while high temp. Dried is ale one.
In experiment, we germinated barley during bud reaches to 3/5 of barley.We done germination process two times.In first trial some buds had 3/5 ratio but the others was higher lenght.So, we did calibration in second trial and soaking water was homogen to all part of towel.But we can not calculate moisture content and amount of water which is used.Unless they are controlled, enzymatic action will not be controlled.
Then some spoilages can be occur at high capacity productions. Also heating conditions are the other important parameters of malt quality, especially Pilsner type beer. Consequently, temp. Of heating step,amount of water at soaking step,calibration must be carefully done during malt pocesses.Also, air condition must be satisfy.
In this experiment we will determine the moisture content of foods by using the methods of moisture determination.The quality of dried food often depends on the levels of moisture left in them. We must determine moisture content for the quality of food.