Puffing

Question 1

what happens to the bulk density of a product that has been puffed

Answer 1

reduced

Question 2

how is bulk density reduced

Answer 2

moisture is removed and structure becomes more porous

Question 3

whhy puff?

Answer 3

prevents shrinking that occur with traditional dehydration which makes rehydration difficult

puffing keeps the product expanded and makes structure more porous so rehydration is easier

Question 4

classifications of puffing processes

Answer 4

phase change puffing
puffing induced by chemical reaction
absorption puffing
adsorption puffing

Question 5

describe phase change puffing

Answer 5

the water in the material is ‘superheated vapour’ = temp higher than 120C
water flash vapourises into a gas which takes up more space creating pressure inside the food

Question 6

explain puffing induced by chemcial reactions

Answer 6

reactions in which the product is gas
CO2 during fermentation
baking soda

Question 7

describe absorption puffing

Answer 7

caused by the reduction of pressure in a saturated system
-soda: has carbonic acid under pressure, release turns it into CO2

Question 8

describe adsorption puffing

Answer 8

gas is adsorbed on the external or internal surface of a product
-used in tobacco processing

Question 9

the organisation of the structure relies on (20

Answer 9

increasing the plasticity of the food surface
rapid phase change of moisture inside the food (flash vapourisation)

Question 10

how can plasticity be improved

Answer 10

blanching followed by light pre-drying

Question 11

what happens to the starch in food products as it undergoes the puffing processes

Answer 11

becomes gelatinised and makes the product more plasticised
-no longer looks like deposits

Question 12

what is ocmmercially used as solid particles on fluidised bed

Answer 12

salt, traditionally sand

Question 13

types of rheological models

Answer 13

spring, linear elasticity: applying force to the string expands, spring will return to normal upon removal of straining
dashpot/linear viscous model : applying force will permentantly change, materia has no strain memory

Question 14

describe the rheological nature of fresh potato

Answer 14

really strong springs that require a lot of force to change

Question 15

describe the rheological nature of blanched/intermediate temp of potato

Answer 15

modified to material be able to respond to any pressure/ improved plasticity

Question 16

describe rheological nature of puffing temp potato

Answer 16

pressure created by flash vapourisation creates pressure on plastiicised material and it expands which creates dashpots
-potato cube is dehydrated which fixes the expansion

Question 17

how many stages to puffing expansion are ther

Answer 17

3
1: strong spring
2: weaker springs, yeilds to force, strong dash pot
3: dashpot

Question 18

how to reverse dashpot formation

Answer 18

applying force in the equal and opposite direction
-crushing the product is an example

Question 19

factors that effect expansion

Answer 19

pre-drying time: there is an optimal time
puffing time/ how long material is kept at puffing temp: increases with time
puffing temp: increases with the temp
sample size: optimal size

all different for different products

Question 20

describe physical conditions required for the production of puffed potato

Answer 20

increase plasticity through blanching
rapid phase change of water to vapour through flash vapourisation

Question 21

describe the thermal conditions required for puffing

Answer 21

blanching >70 but <90
flash vapourisation >120