DSCI 231 Final
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Why do we concentrate milk?
- Reduce volume and weight
- Inhibit growth of microorganisms
- preserve food/extend shelf life
- Water Removal
Why is vacuum evaporation used over atmospheric evaporation for milk concentration?
- *Pressure less than atmospheric pressure
- Boiling point lowered due to partial vacuum
- Removal of latent heat of vaporization
What is typical proximate composition of various dairy ingredients?
Describe the basic processes of vacuum evaporation and spray drying? What are the key parts and the function of these parts of evaporators and dryers?
- Vacuum evaporation- Pressure less than atmospheric pressure, boiling point lowered,heat is transferred from the steam to the food, vapors removed from boiling liquid
- Spray Drying- dispersion of the concentrate into very fine droplets, mixing of the concentrate into a steam of hot air which quickly evaporates the water, separate the dry milk particles from the drying air
Why is a falling film evaporator preferred to a batch evaporator for concentration of dairy fluids?
- Minimum temperature differences
- More effects
Concentrate to: 40-50% total solids (milk)
What is cross flow filtration and how does it differ from dead end filtration?
Dead end filtration is used for separation of suspended particles larger than 10um
What is permeate? What is retentate?
- Permeate: the filtrate, the material which passes through the membrane
- Retentate: the concentrate, the material which does not pass through the membrane
What is semi-permeable membrane?
a membrane that allows some constituents of a feed to pass while retaining other constituents
What distinguishes one membrane process from other membrane processes?
- a process for the filtration of solutions and/or suspensions under pressure through a semi permeable membrane
- Molecular or macromolecular sieve
What are the differences in permeate composition when you process milk through RO NF, UF, or MF membranes?
- RO: 0.0001 um, Ionic, Molecular weight=100
- NF: 0.001 um, Molecular
- UF: 0.01 um, Molecular and macromolecular
- MF: 1.0 um, Macromolecular and Cellular+Microparticulate
What is permeate flux?
permeate flow rate per unit membrane area
What are some of the differences in composition of frozen desserts?
- Super Premium: low overrun, high fat, high quality
- Premium: low overrun, higher fat
- Regular: meets overrun required for federal standard
- Economy: meets required overrun, sells for cheaper
- Gelato: no standard, lower fat, more dense
- Frozen Yogurt: varies (acidity, cultures)
- Soft Serve: "Dairy Dessert" ice cream
What are the key components of the legal definition of ice cream?
Ice cream is a food produced by freezing, while stirring, a pasteurized mix…ice cream contains not less than 1.6 lbs of total solids to the gallon and weights not less than 4.5 pounds to the gallon. Ice cream contains not less than 10% milk fat, nor less than 10 percent nonfat milk solids...
What are typical ice cream ingredients and what are their functions in this system?
- Sources of Fat
- Sources of Milk Solids Non fat (protein, lactose, minerals)
- Nutritive and Non-nutritive sweeteners
- Stabilizers and Emulsifiers
- Flavors, Inclusions, Variegates, Colors
What is overrun?
Ice Cream is 50% air by volume or 100% Overrun
Incorporation of air into ice cream mix
What are the steps involved in converting ice cream mix to ice cream and what are the dynamic changes which occur to the product?
Pre-heating-> Formulation Mixing-> Pasteurisation Homogenisation Cooling-> Ageing (>4 hours) -> Continuous Freezing (<-Air) Added Mixture of Dry Ingredients-> Filling Extrusion Moulding-> Continuous Hardening-> Cold Storage -250C, 0-9 months
Why does the concentration of sugar in the unfrozen phase of ice cream increase as the temperature is lowered?
What causes ice crystal size to be the smallest?
- Low Temperature Extrusion (double churned)
- The more water frozen in the freezer barrel, the smaller the ice crystals
- The "sharper" the freezer blades, and the faster their rotation
What contributes to large ice crystals in frozen desserts?
- less water frozen in the freezer barrel, the larger the ice crystals will be after hardening
- dull freezer blades, and slower rotation, the larger the crystals will be when scraped from the freezer barrel
What are the differences in operation of batch freezers and continuous freezers?
- Continuous Freezer:to whip a controlled amount of air into a mix and to freeze the water content in the mix to a large number of small ice crystals
- Freezing process is very rapid
What does "slow churning" produce smoother ice cream texture compared to other freezing processes?
- Smaller Ice Crystals
- Improved foam stability
- Smaller air cell size
- Higher % water frozen prior to hardening
Why does the textural quality of ice cream erode with freezer storage time?
More ice crystals form
What is phase inversion?
- Churning & Fat Concentration
- Salting, packaging and storage
What are dairy examples of o/w emulsion? w/o emulsion?
- Oil in water emulsion= Cream
- Water in oil emulsion= Butter
What are the differences in buttermilk you buy in milk cartons in the store an the buttermilk that is obtained from churning of cream?
- Buttermilk is the liquid left over from churning butter.
- Buttermilk from the store is cultured low fat milk
What is the proximate composition of butter?
- Water- 15.87
- Total Lipids-81.11
- Total Carbohydrate-0.06
*Salt approximatley 1-2%, other minerals 0.7-0.9%
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