L3B Milk Processing (products) Flashcards
How is yoghurt made?
Converting lactose to lactic acid by the addition of starter culture under the right temp. and moisture conditions.
What is starter culture?
Starter Culture
Contains typically a mixture of two symbiotic bacteria (mixed culture)
Streptococcus thermophilus
Lactobacillus delbrueckii ssp. Bulgaricus
What is the difference between set type yoghurt and swiss type yoghurt?
The two styles of yogurt commonly found in the grocery store are set type yogurt and swiss style yogurt. Set type yogurt is when the yogurt is packaged with the fruit on the bottom of the cup and the yogurt on top. Swiss style yogurt is when the fruit is blended into the yogurt prior to packaging.
How much SNF must yoghurt contain?
at least 8.25%
What is the difference between staphylococcus thermophilous and lactobacillus delbrueckii ssp. bulgaricus?
Streptococcus thermophilus
Heterofermentor – bacteria which produce >1 compound e.g. lactic acid or ethanol
Non-proteolytic – i.e. does not secrete a protease to digest proteins to get amino acids
L. delbrueckii ssp. bulgaricus
Homofermentor – bacteria which produce only 1 compound e.g. lactic acid
Proteolytic – secretes a protease to digest proteins to get amino acids
Explain the process of yoghurt formation.
Step 1:
ST grows exponentially while LD does not as ST uses the amino acids and peptides that are readily available in milk and has fewer nutritional requirements hence growing faster than LD. Amino acids eventually become a limiting factor as ST does not secrete protease.ST also produces formic acid which is later used by LD.
Step 2:
ST growth slows down and LD grows exponentially.ST produced the metabolites necessary for LD. (Formic acid which is required to synthesise purines in DNA. LD lacks pyruvate-formate lyase necessary for formate synthesis whereas ST produces large amounts.
Step 3:
The second exponential growth of ST. LD expresses a protease PrtB anchored on the cell wall. PrtB breaks down casein proteins into peptides, uptake of peptides and release of amino acids. LD also produces lactic acid which lowers the pH eventually causing milk to coagulate.(pH=5.5). The lactic acid and amino acids are what stimulate the growth of ST.ST also secretes an exopolysaccharide that forms a matrix with milk proteins to give a gel like structure.
Step 4:
ST produces more formic acid till pH drops to 5.5 and LD resume its growth causing the pH to drop further to 4.3-4.5.Fermentation process is then slowed down by cooling yoghurt to 4 degrees celsius and the final pH drops to 4.2
What is the general yoghurt making process flow?
Adjust Milk Composition & Blend Ingredients
may be adjusted to achieve the desired fat and solid content.often dry milk is added to increase the amount of whey protein for texture and ingredients such as stabilizers are added.
Pasteurize Milk
Pasteurized at 85 degrees Celsius for 30min or 95 degrees for 10min. High heat treatment is used to denature whey proteins allowing them to form a more stable gel which prevents separation of water during storage. High heat treatment also further reduces the spoilage microorganisms numbers in the milk to provide a better environment for starter culture to grow. Yoghurt is pasteurized before starter cultures are added to ensure they remain active in yoghurt after fermentation as probiotics. If pasteurisation happens after fermentation culture will be inactivated.
Homogenize
Done to improve yoghurt consistency
Cool Milk (42 degrees Celcius) bring the yoghurt to the ideal temperature for starter culture
Inoculate with Starter Cultures
Hold
Milk is held at 42 degrees Celcius until pH 4.5 is reached. Allows fermentation to progress to form a soft gel and the characteristic flavours of yoghurt. Can take several hours.
Cool
Cooled to 7 degrees celcius to stop the fermentation process
Add Flavors & Fruit
Package
What is ice cream?
Ice cream is a complex colloidal system of dispersed and clustered fat droplets in a concentrated mixture of sugars and proteins, with the additional presence of dispersed ice crystals, and air bubbles.
What is the purpose of fat, proteins and emulsifiers in ice cream?
Fats are important for the creaminess of the ice cream.
Proteins from milk form a membrane around fat droplets making them hard to come into contact with one another.
Emulsifiers replace some milk proteins on the surface of the fat droplets.
As ice cream is made some of the fat in the droplets solidify, and the fat “needles” that form help droplets to cluster. These clusters along with milk proteins, help stablise air bubbles in the ice cream.( Membrane consists of emulsifiers and milk proteins that enclose liquid fat which is mixed in with some solid fat crystals)
How do the emulsifiers affect fat droplets?
Replacing some of the proteins with emulsifiers leads to a thinner membrane meaning they are more likely to coalesce and cluster during whipping. This makes them more likely for fat droplets to mix with each other instead of creating an emulsion.
Why do fats need to be de-emulsified in ice cream?
Some of the fat needs to be de emulsified because it plays an important role in trapping air.
What is the structure of ice cream and how is it formed?
The structure of ice cream is 30% ice crystals,15% liquid syrup,5% fat globules and 50% air bubbles.
During freezing, most water is frozen into ice. Small ice crystals are needed for smooth ice cream. Beating and aeration occur at the same time as freezing to form small air bubbles, stabilised by the de emulsified fat. Air makes up 30-50% of the ice creams final volume. Sugar sweetens the ice cream and lowers the freezing point of water, reducing the amount of ice. Soft ice cream contains less ice.
How are the fat globules formed in ice cream?
Fat is forced through a small valve under high pressure to break into small droplets, milk proteins stick to the surface of these droplets creating a membrane. This membrane of proteins helps prevent fat from coalescing back into bigger droplets as the proteins coating individual fat droplets repel each other when they come into close contact.
Why is the melting temperature of fat important in ice cream?
Melting temperature of fat used in ice cream is important as fats that melt at too high temperatures give a waxy feel in the mouth whilst its difficult to make stable ice cream with those that melt at too low temperature.
Dairy falls into the right range, pal oil and coconut oil can also be used as they have similar melting points.
What substances help incorporate air into products?
Fats and proteins. eg sobert do not have dairy products.
How does air content affect ice cream quality?
Better ice creams tend to have lower air content and hence a higher density while higher air density ice cream tends to melt more quickly.
What is the freezing process in ice cream?
Freezing adds the ice itself to the ice cream, modern facilities use liquid ammonia to produce low temperatures before that, mixtures of salt and water were used. Adding salt and water can lower temperatures to -21.1 degrees Celsius whereas liquid ammonia is used at around -30 degrees celsius. The quicker the refrigerant used the quicker the ice cream is made. Ice cream is made in a barrel with rotating scraper blades, when the ice cream touches the sides of the barrel, it freezes but is immediately scraped off by the blades. The very small ice crystals will then be dispersed throughout the mixture. We want thecrystals to be as small as possible as the smaller the crystals the smoother the ice cream.
How are stabilisers used in ice cream?
Stabilisers are added in small amounts about 0.2% into ice cream. They are often extracted from plants (sodium alginate) the sodium salt of alginic acid is extracted from brown seaweeds.
Stabilisers reduce the rate at which ice cream melts, add smoothness and increase the viscosity of liquid phase of ice cream. Using multiple stablisers can produce synergistic effects.
Another stabiliser is carrageenan (less frequently used due to its cost)
How are flavours and colourings incoporated into ice cream?
Natural ice cream flavours contain a number of flavouring contributing compounds. Flavouring can usually be achieved artificially, artificial flavouring often called vanillin other can be more complex. Other compounds like skatole also found in feces which has a flavoural and odour at low concentrations. Colours can be added artificially, anthocyanins from plants among other colouring agents are used.
What are the general percentage of ingredients used for ice cream?
Milkfat: >10% - 16% Milk solids-not-fat (snf): 9% - 12% Sucrose: 10% - 14% Corn syrup solids: 4% - 5% Stabilizers: 0% - 0.4% Emulsifiers: 0% - 0.25% Water: 55% - 64%
Note minimum milk fat in ice cream is 10%
What is the difference between soft-serve ice cream and hard frozen ice cream?
Soft serve ice cream has less milk fat and more air than harder ice cream. Hard ice cream is usually served at -12 degrees Celsius. Soft serve ice cream is served at -6 degrees Celsius. A difference of only 6 degrees makes soft serve ice cream much softer and creamier than its harder cousin.
What is fat destabilization?
Fat destabilization or fat agglomeration refers to the process of clustering and clumping (partial coalescence) of the fat globules which leads to the development of a continuous internal fat network or matrix structure in the product.
What is the purpose of milkfat or butterfat in ice cream?
Milkfat (or “Butterfat”) / Fat
- increases the richness of flavour in ice cream
- produces a characteristic smooth texture by lubricating the palate
- helps to give body to the ice cream, due to its role in fat destabilization
- aids in good melting properties, also due to its role in fat destabilization
- aids in lubricating the freezer barrel during manufacturing
What is the purpose of SNF in ice cream?
The serum solids or milk solids-not-fat (MSNF) - lactose, caseins, whey proteins, and minerals (ash content)
- improve the texture of ice cream, due to the protein functionality
- help to give body and chew resistance to the finished product
are capable of allowing a higher overrun without the characteristic snowy or flaky textures associated with high overrun, due also to the protein functionality
