Lektion 31/3 - principles of cheese making

Question 1

Vad är det första som görs med ost mjölken?

Answer 1

Separation and fat standardisation

Question 2

Vadför temp och tid för thermisation och partösisering

Answer 2

• (Thermisation 63°C for 10-15 s)
• Pasteurisation 72°C for 15-20 s
(not always employed)

Question 3

Hur kan man mekaniskt ta bort bakterier

Answer 3

– Mechanical reduction of bacteria

• Bactofugation, microfiltration

Question 4

Vad tillsätts i ostmjölken för att få smak och stelna. Safety?

Answer 4

Conditioning of cheese milk: additives
– Calcium chloride (reduces pH)
– Inhibition of spores: Saltpetre, sodium nitrate (if permitted by law)

• Lysozyme
– Starter bacteria, appropriate to cheese type
– Coagulant (rennet)

Question 5

Hur mycket procent fett måste man ha i mjölken för att få 60% i osten

Answer 5

5.5-6.0%

Question 6

After 24 hours of storage at +5°C påverkan på ost mjölken

• med ca
• caseinerna
• microflora

Answer 6

– 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)

Question 7

Vad sker med ca och beta carein när man värmer mjölken

Answer 7

Calcium re-dissolves (går tillbaka) and ß-casein migrates back into micelle almost completely upon heat treatment

Question 8

Varför therminiseras långkyld mjölk?

Answer 8

Thermisation introduced to arrest growth of psychrotrophic microflora when milk was stored for another 12-48 hours after arrival at the dairy

Question 9

Role of calcium chloride konsentration (CaCl2) in

cheese making

Answer 9

• 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

Question 10

Vad sker vid Pre-ripening of cheese milk

Answer 10

Inoculation of starter culture (mesophilic,

thermophilic, mixed strain cultures)

Question 11

Role of starter culture:

Answer 11

– 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

Question 12

varför pre-ripe the cheese

Answer 12

• Aim: to initiate growth of starter culture

Question 13

Renneting - varför

Answer 13

• 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

Question 14

när börjar the cutting av ostmassan

Answer 14

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)

Question 15

Hur skärs ostmassan?

Hur påverkar det osten?

Answer 15

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

Question 16

Vilka krav finns det på stirring? Varför görs det?

Answer 16

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

Question 17

Hur påverkar labs syneresen?

Answer 17

Starter bacteria continue to produce lactic acid during this step, favours syneresis

Question 18

Hur mycket whey tas bort i första steget?

Varför görs det?

Answer 18

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

Question 19

hur värms ostmassan upp?

Answer 19

Heating
– by steam in tank jacket
– by addition of hot water into curd/ whey mixture

Question 20

vad sker med startekulturen vid uppvärmning?

Hur påverkar det osten?

Answer 20

• Starter culture continues to produce acid

* Heating also regulates the amount of acid-producing bacteria, controlling pH of the cheese curd

Question 21

Varför är man försiktig med uppvärmning o omrörning?

Answer 21

• 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)

Question 22

hur är aktiviteten av starterkulturen påverkad av temp

Answer 22

Activity of starter cultures
– At 37-38°C greatly inhibited
– At 44°C completely inhibited
– Thermophilic bacteria will not be ihibited at 55°C

Question 23

Final (Post-) stirring

• vad sker
• hur lång tid är det här steget?

Answer 23

• 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

Question 24

Hur fås Granular-eyed cheese

vad innebär detta?

Answer 24

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.

Question 25

Hur fås Round-eyed cheese vad innebär detta?

Answer 25

• 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
disappear.

Question 26

Hur fås Closed-texture cheese vad innebär detta?

Answer 26

• 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

Question 27

Purpose of pressing

Answer 27

– Give cheese its final shape
– Assist final whey expulsion to obtain a certain moisture content
– Provide texture, knit the curd together

Question 28

Crucial prameters during pressing

Answer 28

Crucial moments during pressing include pressure, time, temperature of curd and curd acidity

Question 29

Different ways to press cheese

Answer 29

– Self-pressing
– Short-term pressing (3-4 hours
– Long-term (16-24 hours

Question 30

NaCl is added for different purposes:

Answer 30

– 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

Question 31

Salt can be applied to cheese in different ways:

Answer 31

– In the whey
– In the curd
– On the surface (dry salting)
– In brine (most common)

Question 32

Ratio of casein to the combination of fat and water (ripening of cheese)
Vad sker om denna är låg resektive hög

Answer 32

• 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)

Question 33

Granular-eyed cheese ripening

• time
• coating
• eyeformation

Answer 33

Granular-eyed cheese
– 15-16°C for 2-3 weeks (development of eyes)
– Waxing or plastic coating
– Ripening store, 11-14°C, 2-24 months

Question 34

Round-eyed cheese ripening

• time
• coating
• eye formation

Answer 34

– 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

Question 35

Close-textured cheese ripening

• time
• coating

Answer 35

– wrapped in cheese cloth, which is then waxed

– Ripening store, 3-8°C, 6-18 months

Question 36

Hur kan man få komjölk att fungera istället för sheep milk

Answer 36

To imitate the flavour, cheese milk from cows should be homogenised to make fat more sensitive to lipase from the inoculated Penicillum roqueforti mould

Question 37

Ripening of white-mould cheese

Answer 37

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

Question 38

Hur länge ska rennetost lagras?

Answer 38

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

Question 39

Vad bryts cassein ner till att bli i osten

Answer 39

cassein - peptid - Aa - Aromatics, organic acids, alkohol, aldehyder
pp

Question 40

Vad bryts triglycerider ner till att bli i osten?

Answer 40

TGA - Fa- esters, secondary alkohols

pp

Question 41

Vad bryts lactos ner till att bli i osten?

Answer 41

pyrovat -diacetyl- acetonin, acetat, ethanol,

pp

Question 42

Hur bryts protein ner i osten?

Hur cotribudes detta till osten?

Answer 42

genom Proteolysis

– 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

Question 43

Lipolysis and fatty acid catabolism during cheese ripening

- hur påverkar lipiderna ostkvaliten?

Answer 43

• 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

Question 44

Origin of lipolytic enzymes in cheese during ripening

- vilka finns?

Answer 44

• Milk lipoprotein lipase (LPL)
• Starter lactic acid bacteria
• Secondary starter microorganisms - mögel
• Non-starter lactic acid bacteria (NSLAB)
• Exogenous lipase preparations

Question 45

Fatty acid catabolism and formation of flavour compounds in cheese
- vad för komponenter bildas

Answer 45

• FFA acids are precursors of many important flavour and aroma compounds
– Methylketones
– Lactones
– Esters
– Alkanes
– Secondary alcohols

Question 46

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

Answer 46

• 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
– Ethanol
• 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

Question 47

Role of starter bacteria

Answer 47

– 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

Question 48

Autolysis of starter bacteria

• varför viktig
• när sker det

Answer 48

– 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

Question 49

Can starter autolysis in cheese be controlled?

Answer 49

– Use of highly autolytic strains
– Deliberate addition of phage
– Salt concentration
– Sub-lethal heat treatment
(cooking temperature)

Question 50

Accelerated cheese ripening?

• skillnad soft hard cheese mognad
• vad sker med osten om man skyndar på mogningen?

Answer 50

• 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

Question 51

Non-starter lactic acid bacteria (NSLAB) betydelse

Answer 51

– 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
and enterococci
– Certain strains may survive pasteurization
– Manufacturing equipment important source (”House flora”

Question 52

Hur påverkar NSLAB ostkvaliten?

Answer 52

– 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

Question 53

Propionic acid bacteria

• varför vill man ha denna?
• Vad metaboliserar den?

Answer 53

PAB metabolize lactate till propionate (smak)+ acetate (smak)+ CO2 (stora hål) + H2O

Question 54

Moulds

• påverkan på osten
• vilka 2 typer finns

Answer 54

• 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)