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Food Physical Systems > Physical Systems Karwe > Flashcards

Physical Systems Karwe Flashcards

1
Q

Density of a simple mixture

A

Simple mixture ignores the chemical reactions

Calculations are on slides

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2
Q

Brix scale

A

Sugar content of an aqueous solution that is purely based on sucrose.

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3
Q

Plato or degrees plato

A

Measure weight of solids dissolved in water measured in %

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4
Q

Density of water-ethanol mixture

A

Adding two liquids of same polarities is not a simple mixture so net volume will be less

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5
Q

Non-Ideal Density of Water-Ethanol mixture

A

Water and ethanol do not mix ideally

Volumetric contraction occurs when mixing water and ethanol leading to a higher-than-expected density at intermediate ethanol concentrations

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6
Q

Alcohol by Volume (ABV)

A

Measured by hydrometers that measure specific gravity of liquid before and after fermentation

Use temperature and ethanol weight % to find density

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7
Q

How to calculate ABV

A

Measure original specific gravity and final specific gravity of ethanol
ABV = (OSG-FSG)x131.25 in %
131.25 is a constant

Density decreases as sugar is converted during fermentation

Specific gravity decreases

Sugar solution of alcohol before fermentation has a density is higher than water

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8
Q

Boiling of Water-Ethanol mixture graph

A

Boiling alcohol at certain temperature results in a different composition of vapor

Ex: 10% alcohol at 90 degrees results in vapor composition of 58% alcohol

Alcohol is more volatile

Alcohol vapor pressure at given temperature is higher than water vapor pressure

If you condense vapor, it will have a composition different from the starting position and the vapor position (move down on the graph to obtain this %)

If boiling move to the right to obtain new ration

Beyond a point (95.6% alcohol) you cannot purify it more through distillation

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9
Q

Bulk density

A

Total volume is the volume of bulk + volume of feed
The air space has no mass
Mass of solid/volume of hole

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10
Q

Density of solid part of porous material

A

Mass of solid/volume of solid
(Vb-Vs)/Vb = 1- (Vs/B) -> 1- ((M/rho solid0/m/rho bulk) = 1 - Rho(bulk)/Rho(solid)

Tells you how much air is in product

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11
Q

Different porosity foods

A

High porosity foods
Meringues, marshmallows, whipped cream

Medium porosity foods
Most meats, fruits and vegetables

Low porosity
Hard cheese chocolate

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12
Q

Overrun

A

Used in manufacturing of productions involving whipping or aeration

Density is important to consider for foaming

Volume increases far beyond original volume
A = (Vfoam - Vliquid)/Vliquid

Mass of foam is also the mass of the liquid

A in % = (Density of liquid/Density of foam)-1 x 100

Air pockets are necessary for ice cream

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13
Q

Density Measurement of Non-standard shape object by pycnometer

A

When valve 1 is open and valve 2 is closed

Measures porosity

Vcell - V sample is volume of the gas

P1(Vcell - Vsample) =n1RT

Fill sample with pressure

Gas expands

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14
Q

Solid Fat Index (SFI) and Solid Fat Content (SFC)

A

SFC: direct measurement of solid fat at various temperatures

SFI: determined by volume changes resulting from melting or crystallization

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15
Q

Dilatometer

A

Measures volume change caused by physical or chemical process
SFI calculation method adopted as convention

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16
Q

SFI

A

Solids and liquid fats expand with temperature

Melt liquid fat as a function of temperature (x axis) to see change in specific volume

Look at the distance between the liquid fat and solid fat

Mixture of two fats should be in between this line

Spreadability is directly a function of SFI (you want a more linear line with temp and SFI)

17
Q

Tortuosity

A

Measures how complicated path is

Higher number, higher tortuosity

Tortuosity characterizes paths of particles transported through the medium

Resists mass transfer

Depends on internal structure and ingredients

18
Q

Porosity

A

Porosity is fundamental number that describes fractions of voids in medium

19
Q

Permeability

A

Permeability defines ability of medium to transport fluid

Mass transfer property

Gas has to adsorb to package via Henrys Law

Diffuses through because of concentration gradient and governed by Fick’s Law

Finally desorbs

20
Q

Particle Size, Shape and distribution

A

Affects production and handling of ingredients and formulation
Particle size affects reactivity, solubility, and flowability of ingredients, and the texture, mouthfeel and processing of products

21
Q

Surface topography

A

Primary waviness with valleys and peaks

Roughness is microscopic

Asperity is highest point on surface and two surfaces touch as asperities

22
Q

Surface roughness

A

Subtracting the waviness from the primary profile results in roughness

Observe fluctuation around mean line

Integrate curve and square the number and divide this by the length

23
Q

Why is surface roughness so important?

A

Microbes can get into surface and detergent can have issues getting into these surfaces

Control surface tension so water can penetrate surface

Little surface tension as possible

Resistance to flow is higher when surface is rougher

Use CLSM to quantify surface roughness

As surface roughness increased, maximum microbial survivor increased

24
Q

Rheology

A

How and why the material flows and deforms

25
Q

Rheological data needed for what reasons

A

Ingredient functionality
Shelf-life prediction and testing
Evaluation of food texture
Process engineering calculations

26
Q

Stress and Strain

A

Normal stress: Force/Area
Normal strain: Fraction of elongation/original length

Relationship between normal stress and normal strain is a straight line and relationship is e

Slope is Hookes Law and the higher value of e, higher stiffness/elasticity

Young’s modulus of elasticity

Newtons/M^2 (PA) for stress

No unit for strain

E has as a unit of Pascals as well

27
Q

Viscosity in relation to rheology

A

Viscosity is shear stress divided by shear rate

As viscosity increases, the time for air bubble to travel increases

Smaller bubbles take longer to go away

28
Q

Shear

A

Shear stress is also Force/Area
Perpendicular
Different than stress
Shear modulus can be graphed

29
Q

Shear Strain

A

Delta X/Delta Y

Y is surface not being strained and x is surface being strained

30
Q

Strain rate

A

First derivative of the ratio of change in length

When y is a constant, it measures how fast top surface moves in relation to time

Velocity/gap is the strain rate

31
Q

Elastic Solid

A

Finite proportional deformation
No flow
Returns to original shape upon removal of stress

32
Q

Plastic Solid

A

Residual strain can occur where material may not return to its original shape

Some recovery upon removal of stress

33
Q

Application of normal stress

A

Compressible materials show a decrease in volume when pressure increases

Water at 690 MPa compresses by 15%

If volume and mass doesn’t change, density is constant

34
Q

Relationship between shear stress and shear rate

A

Shear stress/shear rate is viscosity

Should be a linear relationship

G is shear modulus and gamma is shear strain

G is how spring like substance and is measured in

Mu resents fluidity of substance and is measured in Pascals*seconds

35
Q

Newtonian vs Non-Newtonian

A

If Mu is constant at a given temperature, it is Newtonian

Newtonian: water, air, oil, honey
Viscosity is glycerin is about 1 Pas while viscosity of water is around 0.0018 Pas

Non-Newtonian materials do not show a proportional change in viscosity while Newtonian materials do
Shear thinning or shear thickening can occur

36
Q

Viscosity divided by density is kinematic viscosity

A

Mu/rho in M^2/s
How fast a disturbance will travel through fluid

Mu controls the property of the signal of disturbance traveling through fluid

Use depth to determine the time it takes for disturbance to reach inhabitants
Depth^2/Mu
If Mu is lower, the time it takes for signal to reach is higher

37
Q

Mu decreasing as temperature increases

A

Corn syrup is Newtonian but highly temperature dependent: More starch is broken down into dextrose, dextrose equivalent number increases and viscosity decreases

Sucrose vs invert sugar: Invert sugar is formed from when glycosidic bond between fructose and sucrose is broken
Molecular weight decreases and thus viscosity is lower in invert sugar
Both temperature dependent

Food Physical Systems (5 decks)

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