Vad är det första som görs med ost mjölken?
Separation and fat standardisation
Vadför temp och tid för thermisation och partösisering
• (Thermisation 63°C for 10-15 s)
• Pasteurisation 72°C for 15-20 s
(not always employed)
Hur kan man mekaniskt ta bort bakterier
– Mechanical reduction of bacteria
• Bactofugation, microfiltration
Vad tillsätts i ostmjölken för att få smak och stelna. Safety?
Conditioning of cheese milk: additives
– Calcium chloride (reduces pH)
– Inhibition of spores: Saltpetre, sodium nitrate (if permitted by law)
– Starter bacteria, appropriate to cheese type
– Coagulant (rennet)
Hur mycket procent fett måste man ha i mjölken för att få 60% i osten
After 24 hours of storage at +5°C påverkan på ost mjölken
- med ca
– 25% of the calcium precipitates with phosphate
– ß-casein dissociates from the casein micelle
– Adaption and growth of psychrotrophic
microflora (Pseudomonas, decomposition of fat and protein by their lipases/ proteases)
Vad sker med ca och beta carein när man värmer mjölken
Calcium re-dissolves (går tillbaka) and ß-casein migrates back into micelle almost completely upon heat treatment
Varför therminiseras långkyld mjölk?
Thermisation introduced to arrest growth of psychrotrophic microflora when milk was stored for another 12-48 hours after arrival at the dairy
Role of calcium chloride konsentration (CaCl2) in
• Addition of CaCl2 (5-20 g/ 100 kg of milk)
– CaCl2 supports action of rennet (lowering pH)
– Less rennet needed
• A too low CaCl2 concentration in milk causes
– Soft coagulum
– Losses of casein and fat in whey
– Poor syneresis
• A too high CaCl2 concentration in milk causes
– Hard coagulum
Vad sker vid Pre-ripening of cheese milk
Inoculation of starter culture (mesophilic,
thermophilic, mixed strain cultures)
Role of starter culture:
– Production of lactic acid from lactose, lowering pH
– Production of CO2(not all cultures)
• CO2 produced by action of citric acid fermenting bacteria
• Essential for production of cheese with a round-eyed or granular-eyed texture
– Protein degradation
• Combined effect caused by endogenous milk proteases, bacterial proteases and rennet whereby milk protein is degraded to peptides and amino acids
varför pre-ripe the cheese
• Aim: to initiate growth of starter culture
Renneting - varför
• All cheese manufacture depends on action of rennet or similar coagulants
– Exceptions are fresh cheese types, e.g. cottage cheese, quarg, in which milk is clotted by lactic acid
när börjar the cutting av ostmassan
Cutting starts at a certain firmness of the gel, a point which is difficult to define, and the decision is taken by the cheesemaker
(typically after 30 minutes)
Hur skärs ostmassan?
Hur påverkar det osten?
Curd is cut in three dimensions, gently broken up into cheese grains with a size of 3-15 mm. The finer the cut, the lower the moisture in the resulting cheese
Vilka krav finns det på stirring? Varför görs det?
Immediately after cutting, the grains are very sensitive to mechanical treatment
– Stirring must be gentle, but
– Stirring must be fast enough to keep grains suspended in the whey and avoid formation of lumps on the bottom of the tank
Hur påverkar labs syneresen?
Starter bacteria continue to produce lactic acid during this step, favours syneresis
Hur mycket whey tas bort i första steget?
Varför görs det?
Normally 30-35% of the initial batch is drained off, sometimes as much as 50% depending on cheese type
– This contributes to a faster syneresis, since the mechanical pressure on the curd will increase during stirring
– Sometimes water is added to decrease the lactose concentration and regulate pH of the cheese curd
hur värms ostmassan upp?
– by steam in tank jacket
– by addition of hot water into curd/ whey mixture
vad sker med startekulturen vid uppvärmning?
Hur påverkar det osten?
- Starter culture continues to produce acid
* Heating also regulates the amount of acid-producing bacteria, controlling pH of the cheese curd
Varför är man försiktig med uppvärmning o omrörning?
- Gentle heating at first to avoid contraction of grain surfaces, which would hinder syneresis
- Combination of stirring, heating and acid development has profound effect on syneresis (moisture) and dissolution of calcium phosphate (texture)
hur är aktiviteten av starterkulturen påverkad av temp
Activity of starter cultures
– At 37-38°C greatly inhibited
– At 44°C completely inhibited
– Thermophilic bacteria will not be ihibited at 55°C
Final (Post-) stirring
- vad sker
- hur lång tid är det här steget?
- More whey is exuded from the grains, due to elevated temperature, continuous lactic acid development and mechanical effect of stirring
- time is depending on the desired acidity and moisture content of the cheese curd, finalising syneresis
Hur fås Granular-eyed cheese
vad innebär detta?
The grains are separated from the whey and exposed to air before being collected and pressed
• A large number of interstices, tiny air pockets, remain in the interior of the cheese • CO2 formed during ripening will fill and gradually enlarge these pocket.
Hur fås Round-eyed cheese vad innebär detta?
• Curd grains are collected, formed and pressed below the surface of the whey to avoid air between the
individual grains. The newly made cheese will be almost entirely closed with only few invisible cavities.
• Gas-producing starter bacteria accumulate in the microscopic, wheyfilled cavities in the curd.
• Formed gas is first dissolved in liquid however later, small holes are formed. Finally, gas diffuses and enlarges some of the holes, while the smaller holes
Hur fås Closed-texture cheese vad innebär detta?
• Grains are collected in a layer for a final acidification period after whey drainage to allow all lactose to be
fermented to lactic acid.
- Curd forms a solid mass of cheese which is milled into pieces (”chips”), which are salted during stirring.
- Finally, cheese curd is formed and pressed
- Since no fermentation takes place during ripening (all lactose fermented) the texture will be closed
Purpose of pressing
– Give cheese its final shape
– Assist final whey expulsion to obtain a certain moisture content
– Provide texture, knit the curd together
Crucial prameters during pressing
Crucial moments during pressing include pressure, time, temperature of curd and curd acidity
Different ways to press cheese
– Short-term pressing (3-4 hours
– Long-term (16-24 hours
NaCl is added for different purposes:
– Flavour of the cheese
– Influence development of the starter culture of the cheese and thereby many of the cheese characteristics
– Influence consistency of the cheese
– Improve keeping quality of the cheese
Salt can be applied to cheese in different ways:
– In the whey
– In the curd
– On the surface (dry salting)
– In brine (most common)
Ratio of casein to the combination of fat and water (ripening of cheese)
Vad sker om denna är låg resektive hög
• Ratio is low: proteolysis cause the cheese to become very creamy and soft
– Soft, creamy, smooth, pasty or sticky (more so if fat decreases)
• Ratio is high: cheese tends to become crumbly or short
– Splits or cracks if gas production after proteolysis
– Poor sliceability, the slices fraacture (Parmesan)
Granular-eyed cheese ripening
– 15-16°C for 2-3 weeks (development of eyes)
– Waxing or plastic coating
– Ripening store, 11-14°C, 2-24 months
Round-eyed cheese ripening
- eye formation
– 10-12°C, 10-14 days
– Waxing or plastic coating
– 16-20°C, 2-3 weeks (development of eyes)
– Ripening store, 11-14°C, 2-24 months
Close-textured cheese ripening
– wrapped in cheese cloth, which is then waxed
– Ripening store, 3-8°C, 6-18 months
Hur kan man få komjölk att fungera istället för sheep milk
To imitate the flavour, cheese milk from cows should be homogenised to make fat more sensitive to lipase from the inoculated Penicillum roqueforti mould
Ripening of white-mould cheese
after the suply of latateis exhaused
1) surface flora produce CO2 och NH3
2) pH increase in the surface
3) calcium phosfate percipates the surface
4) ca2+gradienten - hög vid ytan och låg i mitten
5) osten mjuknar på insidan pga mindre ca2+
overall increase in pH over time increase the plasmin-induced proteolysis
ripening driven by pH and ca2+ gradients from the outside in
Hur länge ska rennetost lagras?
Rennet coagulated cheeses are ripened for a period of 2 weeks to ≥2 years during which flavour and texture characteristic of the cheese variety develop
Vad bryts cassein ner till att bli i osten
cassein - peptid - Aa - Aromatics, organic acids, alkohol, aldehyder
Vad bryts triglycerider ner till att bli i osten?
TGA - Fa- esters, secondary alkohols
Vad bryts lactos ner till att bli i osten?
pyrovat -diacetyl- acetonin, acetat, ethanol,
Hur bryts protein ner i osten?
Hur cotribudes detta till osten?
– Development of cheese texture
• Hydrolysis of protein matrix of cheese
• Decrease in aw (pp)
– Flavour (perhaps also off-flavour) of cheese
• Directly by production of short peptides and amino acids, some of which have flavours
• Indirectly by the liberation of amino acids
Lipolysis and fatty acid catabolism during cheese ripening
- hur påverkar lipiderna ostkvaliten?
• Lipids play a major role in cheese quality :
– They affect cheese rheology and texture
– Affect flavour (perhaps also off-flavour) of cheese
• Lipids act as source of fatty acids which may be catabolized to other flavour compounds
• Many reactions occur at the fat-water interface
• Fat absorbs bitterness of hydrophobic peptides, therefore low-fat cheeses tend to develop bitter taste
Origin of lipolytic enzymes in cheese during ripening
- vilka finns?
- Milk lipoprotein lipase (LPL)
- Starter lactic acid bacteria
- Secondary starter microorganisms - mögel
- Non-starter lactic acid bacteria (NSLAB)
- Exogenous lipase preparations
Fatty acid catabolism and formation of flavour compounds in cheese
- vad för komponenter bildas
• FFA acids are precursors of many important flavour and aroma compounds – Methylketones – Lactones – Esters – Alkanes – Secondary alcohols
Metabolism of residual lactose, lactate and citrate during cheese ripening
- hur fermenteras laktos?
- Varför är lactate viktigt?
- var bildas frå lactate?
förstår ej vad jag menar
• Residual lactose is fermented to lactate by LAB
• Lactate is an important substrate for a series of reactions in cheese during ripening, mainly converted to ”secondary” lactose metabolites by LAB, e.g.
– CO2, acetic acid, ethanol, propionic acid
– Acetic acid
• Gives added sharpness
• Reacts with methane thiol to produce cheesy thiomethyl ester
• Reacts with FFA to produce fruity esters
• Non-aerobic metabolism of lactate to butyric acid by Clostridium tyrobutyricum (+CO2, H2)
• Citrate is only metabolized by certain (cit+) strains of lactococci, producing diacetyl, acetate, acetoin and CO2
Role of starter bacteria
– Primary function production of acid during fermentation
– Also contribute to cheese ripening, with enzymes participatingproteolysis and amino acid catabolism
– Only significant contribution to microbial biomass of LAB in curd
Autolysis of starter bacteria
- varför viktig
- när sker det
– Essential parameter to control and accelerate cheese ripening
– Due to enzymatic degradation of cell wall peptidoglykan by endogenous peptidoglykan hydrolases (autolysins)
– Generally occurs under unfavourable
conditions, including starvation
Can starter autolysis in cheese be controlled?
– Use of highly autolytic strains – Deliberate addition of phage – Salt concentration – Sub-lethal heat treatment (cooking temperature)
Accelerated cheese ripening?
- skillnad soft hard cheese mognad
- vad sker med osten om man skyndar på mogningen?
- A soft cheese has a high eating quality during a short time
- A long-ripened cheese takes takes longer to produce but has a high eating quality during a long time
- Use of accelerated ripening, e.g. by use of a more proteolytic starter culture, will give a shorter time with high eating quality
Non-starter lactic acid bacteria (NSLAB) betydelse
– Significant proportion of the microflora in all ripened cheese varieties
– Normally not deliberately added but adventitious contaminants
which grow during ripening
• Typical non-starter bacteria include lactobacilli, leuconostocs, pedicocci
– Certain strains may survive pasteurization
– Manufacturing equipment important source (”House flora”
Hur påverkar NSLAB ostkvaliten?
– Inclusion of adjunct NSLAB results in improved flavour intensity, increased aroma and accelerated ripening
– Presence of adventitious NSLAB introduces variability in the ripening process that can not be controlled by the cheesemaker
Propionic acid bacteria
- varför vill man ha denna?
- Vad metaboliserar den?
PAB metabolize lactate till propionate (smak)+ acetate (smak)+ CO2 (stora hål) + H2O
- påverkan på osten
- vilka 2 typer finns
• Mould ripened cheese divided in two groups:
– Ripened due to presence of Penicillum roqueforti
• Spores added to cheese milk, cheese pierced before ripening.
• Ripened due to growth of Penicillum camemberti on the surface of the cheese (e.g. Camembert, Brie)
– White felt of P. Camemberti develops on surface of cheese within first week. Lactate converted to CO2 and H2O, surface de-acidified and become basic due to NH3 production.
• Moulds associated with a range of other cheese varieties as well
– Mucor on the surface of Taleggio (It), Gammelost (N)