Etiket Arşivleri: Coagulation

Cheese Making

Cheese making

Introduction

• Cheese is a generic term for a diverse group of milk- based food products. Cheese is produced throughout the world in wide-ranging flavours, textures, and forms.

• Cheese consists of proteins and fat from milk, usually the milk of
cows, buffalo, goats, or sheep. It is produced by coagulation of the milk protein casein.

Objective of cheese making

 To obtain the optimum cheese composition with respect to moisture, acidity (pH), fat, protein and minerals (especially calcium)

 Establish the correct structure of the cheese at the microscopic level; and

 Ripen to perfection. Grouped according to texture and basic manufacturing procedures there are seven families of cheese.

First Step
• Milk from the evening milking is allowed to stand overnight. By natural processes, this milk will have partially separated during its overnight standing period. The cream is skimmed off, and the partially skimmed milk is combined with whole milk from the morning milking.

Second Step
The milk is gradually heated to 30 to 35 C (86 to 95 F) before acidification and coagulation.

Step 3

• Acidification: Starter culture is added to milk to change lactose (milk sugar) into lactic acid. This process changes the acidity level of the milk and begins the process of turning milk from a liquid into a solid.

Starter culture

• Fermentation starters (called simply starters within the corresponding context) are preparations to assist the beginning of the fermentation process in preparation of various foods and fermented drinks. A starter culture is a microbiological culture which actually performs fermentation.

Step 4

Coagulation: Rennet is added to further encourage the milk to solidify , forming a custard -like mass. rennet

• .Rennet An enzyme used to coagulate milk during the cheese making process. Rennet is derived from one of four sources: the stomach lining of a young calf (the enzyme rennin is found in the stomach lining of animals because it aids in the digestion of their mother’s milk)

• plants (typically thistle)

• microbes in fungus and yeast

• Genetically engineered rennet that imitates animal rennet.

Step 4

Cutting:- It’s then cut into small pieces to begin the process of separating the liquid (whey) from the milk solids (curds).Large curds are cooked at lower temperatures , yielding softer cheeses like Mascarpone and Ricotta. Curds cut smaller are cooked at higher temperatures, yielding harder cheeses like Gruyere and Romano

Step 5

Stirring, Heating & Draining:- Cheese makers cook and stir the curds and whey until the desired temperature and firmness of the curd is achieved. The whey is then drained off, leaving a tightly formed curd.

Here you can see the cheese maker taking some of the whey out of the vat.

Step 6

• Salting: Salt adds flavour and also acts as a preservative so the
cheese does not spoil during long months or years of ageing. It also
helps a natural rind to form on the cheese. There are several ways to use salt. Salt can be added directly into the curd as the cheese is
being made. The outside of the wheel of cheese can be rubbed with salt or with a damp cloth that has been soaked in brine. The cheese
can also be bathed directly in vat of brine. Concentrated brine. adding the salt directly into the drained curd

Step 7

 Curd Transformation
Different handling techniques and salting affect how the curd is transformed into the many cheese varieties made.

• Shaping:

Step 8

The cheese is put into a basket or a mold to form it into a specific shape. During this process, the cheese is also pressed with weights or a machine to expel any remaining liquid. Pressing determines the characteristic shape of the cheese and helps complete the curd formation. Most cheeses are pressed in three to 12 hours, depending on their size.

Step 9

Ripening: Referred to as affinage, this process ages cheese until it
reaches optimal ripeness. During this process, the temperature and humidity of the cave or room where the cheese ages is closely monitored. For some cheeses, ambient molds in the air give the cheese a distinct flavour. For others, mold is introduced by spraying it on the cheese (brie) or injecting it into the cheese (blue cheese). Some cheeses must be turned, some must be brushed with oil, and some must be washed with brine or alcohol.

Aging should take place in a controlled environment. Different cheeses required different temperatures and humidity’s, however in a small refrigerator temperature is kept at 55°F and 85% humidity. During aging , the cheese should be rotated or flipped periodically to prevent moisture from settling in the cheese and to prevent an inconsistent internal consistency.

Mechanisms of Coagulation ( Paul S. Kindstedt )

What are casein micelles? Calcium phosphate Polar surface Non-Polar interior layer, rich in (rich in Alpha-s1, Kappa-casein Alpha -s2, Beta casein) Adapted from: Horn, D. 1998. International Dairy J. 8:171- 177

Kappa casein nonpolar + + polar AA 169

Calcium phosphate Polar surface Non-Polar interior layer, rich in Kappa-casein (rich in Alpha-s1, Alpha -s2, Beta casein) Adapted from: Horn, D. 1998. International Dairy J. 8:171- 177

Mechanisms of coagulation • Rennet (rapid: 30 – 60 min) • Acid (slow: 5 – 24 hr) • Acid-rennet (slow: 12 -24 hr) • Acid-heat

What is rennet? • General term for enzymes used to coagulate milk • Technically restricted to enzymes derived from ruminant stomachs • All are protein degrading enzymes (proteinase, protease, proteolytic enzyme) • All are members of the aspartic proteinase family

All aspartic proteinases have 2 characteristics in common aspartic aspartic – – Source: after Crabbe, M.J.C. 2004. Rennets: General and molecular aspects In Cheese: Chemistry, Physics and Microbiology, Elsevier Academic Press, London

Kappa casein is uniquely vulnerable to the action of aspartic proteases nonpolar AA 105-106 + (very vulnerable + to aspartic proteinases) polar AA 169

Rennet cleavage of kappa casein Kappa casein chymosin, etc. – + + – – – – – – – – –

Rennet coagulation occurs in two phases 1. Enzymatic 2. Non-enzymatic

1. Enzymatic phase: cleavage of k-casein Rennet enzymes shave off polar surface Adapted from: Horn, D. 1998. International Dairy J. 8:171- 177

1. Enzymatic phase: cleavage of k-casein casein micellecasein micelle Kappa-Casein with exposed polar region

2. Nonenzymatic phase: Ca++ induced aggregation casein micelle ++ Ca Ca++ Ca++ Ca++ VERY Nonpolar surface CMP/GMP (AA106-169)

2. Nonenzymatic phase: aggregation of casein micelles + Ca+ + Permanent bonding Nonpolar micelles (commences after 80-90% cleavage of k-casein)

2. Nonenzymatic phase continued: chain formation/flocculation visible flocs = rennet clotting time

continuous gel – coagulation

Matrix rearrangement Fine matrix – small coarse matrix – large pores, firm gel pores,weak gel

Repercussions of matrix rearrangement • Cheese moisture content • Acid development during cheese making • Cheese yield

Matrix rearrangement Coarse matrix contracts, Fine matrix – small syneresis pressure ­ pores,weak gel

Repercussions of matrix rearrangement 1. Cheese moisture content • Cutting early (weak set) enables much rearrangement to occur after cutting; syneresis ­, cheese moisture content Ø – ex: alpine cheeses • Cutting late (firm set) limits rearrangement after cutting; syneresis Ø, cheese moisture content ­ – ex: traditional Brie, Camembert • Cutting firmness should be consistent from vat-to-vat to reduce moisture variation

Repercussions of matrix rearrangement 2. Acid development • If the amount of time to the desired cutting firmness varies greatly from day-to-day, the subsequent rate of acidification during the rest of cheese making may be affected: – Extended cutting time, ­ starter culture population, ­ rate of acidification – Reduced cutting time, Ø starter culture population, Ø rate of acidification • Therefore, both cutting firmness and cutting time should be optimized and held constant from day-to- day

Bottom line • Cutting should be initiated at a consistent curd firmness that is optimized for the type of cheese being made • The time required to achieve the target cutting firmness should be consistent from vat-to-vat across season • In practice, this can be challenging because several factors may influence coagulation and cause curd firmness at cutting and/or cutting time to vary

Repercussions of matrix rearrangement • Cheese moisture content • Acid development during cheese making • Cheese yield

Repercussions of matrix rearrangement 3. Cheese yield • Weak curds are fragile and tend to shatter during cutting – fat and casein losses ­, cheese yield Ø – however, matrix rearrangement after cutting occurs rapidly, curd particles firm up quickly • Firm curds are more forgiving with respect to shattering during cutting – however, matrix rearrangement after cutting occurs slowly – curd particles firm up slowly and remain vulnerable to shattering for longer time after cutting

Mechanisms of coagulation • Rennet (rapid: 30 – 60 min) • Acid (slow: 5 – 24 hr) • Acid-rennet (slow: 12 -24 hr) • Acid-heat

Acid coagulation 1. Starter culture 3. H+ ions produces lactic acid, neutralize the H+ ions accumulate negative charges on k-casein H+ H+ H+ H+ H+ H+ H+ H+ 2. Calcium phosphate 4. Neuralized dissolves into k-casein collapses water phase

Acid coagulation H+ pH 4.6 Collapsed neutralized Polar k-cn nonpolar surface Surface Micelle rich in Micelle depleted of calcium phosphate calcium phosphate

Aggregation of casein micelles continuous gel – coagulation

Acid coagulation • Acid gels lack the capacity to contract and synerese • Therefore, final cheese moisture content is very high (around 70-80%, depending of the fat content) • In general, acid coagulated cheeses are eaten fresh, not ripened

Mechanisms of coagulation • Rennet (rapid: 30 – 60 min) • Acid (slow: 5 – 24 hr) • Acid-rennet (slow: 12 -24 hr) • Acid-heat

Key parameters of acid-rennet coagulation 1. Amount of rennet added to the milk: – Anywhere from 1 – 30% of the level used in rennet coagulation 2. Coagulation temperature: – Anywhere from 18 – 32°C

Example 1: Quark • Lactic fermentation at ca. 30°C for 16 hr • A small amount of rennet (e.g., 1 – 10% of level used in rennet coagulation) added at around pH 6.3 • Rennet proceeds through enzymatic and non- enyzmatic phases as milk pH Ø • Coagulation occurs at pH 4.8 or 4.9 instead of ph 4.6 • The resulting curd develops hybrid characteristics that fall somewhere between those of rennet curd and acid curd

Advantages of acid-rennet coagulated Quark –Better draining results in a lower moisture content – Lower moisture content along with a firmer coagulation result in a firmer cheese body, improved texture –Higher cutting pH (e.g. from pH 4.6 to 4.8 or 4.9) results in a less acidic flavor

Example 2: soft ripened goat ’s milk cheese • The milk undergoes lactic acidification at around 20°C for 24 hr • Rennet (about 1/3 the level used in rennet coagulation) is added, often around pH 6.3. • The rennet proceeds through enzymatic phase but the non-enyzmatic phase is strongly impeded at 20°C, • Coagulation occurs in 24 hr when the pH reaches around pH 5.3 • The resulting curd develops hybrid characteristics that fall somewhere between those of rennet curd and acid curd

Advantages of acid-rennet coagulation for goat’s cheeses • Syneresis is improved, resulting in a final cheese with ca. 60-70% moisture. • This moisture range is low enough to support controlled ripening • The end result is a group of soft ripened goat’s milk cheeses with a unique lactic acid dominated texture

Factors that affect rennet coagulation • Temperature history of milk • pH of milk during coagulation • Temperature of milk during coagulation • Ca++ ion content of milk • Casein content of milk

Temperature history of milk: 1. Cooling (< 10ºC) H+ Ca++ ß- casein HPO4 = 0.2 – 0.3 pH ­

Repercussions of cooling milk to 4ºC • ­ milk pH – Slower enzymatic phase – Ø attraction between rennet enzymes and casein micelles, ­ cleavage of k-casein needed to induce coagulation – Therefore, longer time needed to attain target cutting firmness • Altered casein micelle structure – Curd matrix less able to undergo structural rearrangement, contraction – Therefore, weaker set, slower syneresis, higher moisture content in cheese (especially in high moisture types, e.g., bloomy rind) • May cause problems when switching from warm milk fresh from the animal to cold stored milk

Compensating for cooling milk to 4ºC • The changes can be largely reversed by normal pasteurization before cheese making • These changes can be partly overcome by adding calcium chloride. • If necessary, increase cutting time to restore the target curd firmness • If necessary, adjust starter usage to restore target acifidification schedule • If necessary, take action during cheese making to enhance syneresis/draining to reduce cheese moisture content

Factors that affect rennet coagulation • Temperature history of milk • pH of milk during coagulation • Temperature of milk during coagulation • Ca++ ion content of milk • Casein content of milk

pH of milk during coagulation pH Ø from 6.7 – 6.0 Ca++ H PO – ß-casein 2 4

Repercussions of milk pH • As milk pH Ø • Rennet enzyme activity increases • Rennet enzymes are more strongly attracted to casein micelles • Therefore, the enzymatic phase occurs more rapidly • Furthermore: • Rennet enzymes adsorb more tightly onto the casein micelle surface, resulting in “patches” of k-casein cleavage • Therefore, the amount of k-casein cleavage needed to induce micelle aggregation Ø • Also, higher Ca++ ion concentration speeds up the aggregation of casein micelles • Therefore, Non-enzymatic phase occurs more rapidly • Consequently, rennet clotting time Ø, cutting time Ø, and curd firmness ­

• Temperature history of milk • pH of milk during coagulation • Temperature of milk during coagulation • Ca++ ion content of milk • Casein content of milk

As coagulation temperature ­ from ca. 25 ° – 40 °C • Enzymatic phase occurs more rapidly: • Rennet enzyme activity increases with ­ temperature • Non-enzymatic phase occurs more rapidly • Rennet enzymes adsorb more tightly onto the casein micelle surface • Therefore, the amount of k-casein cleavage needed to induce micelle aggregation Ø • Consequently, rennet clotting time and cutting time Ø, and curd firmness ­

As coagulation temperature Ø from ca. 25 ° – 15°C • Enzymatic phase gradually slows down but the non-enzymatic phase fails catastrophically – At 20°C, the non-enzymatic phase is severely impeded and casein aggregation/curd formation occurs very slowly (many hours) – This principle is exploited in the production of acid-rennet coagulated cheeses – At 15°C, the nonenzymatic phase is completely prevented; casein aggregation cannot occur even when k-casein has been completely cleaved from the micelle surface • Bottom line: coagulation temperature should be tightly controlled

Factors that affect rennet coagulation • Temperature history of milk • pH of milk during coagulation • Temperature of milk during coagulation • Ca++ ion content of milk • Casein content of milk

Ca++ ion content of the milk casein micelle ++ Ca Ca++ Ca++ Ca++ VERY Nonpolar surface CMP/GMP (AA106-169)

Calcium chloride addition • Supplies Ca++ ions, enables nonezymatic phase (aggregation of casein micelles) to proceed • Decreases the milk pH, thereby stimulating the enzymatic phase • End result: rennet clotting time Ø, cutting time Ø, and curd firmness ­

Factors that affect rennet coagulation • Temperature history of milk • pH of milk during coagulation • Temperature of milk during coagulation • Ca++ ion content of milk • Casein content of milk

As casein content ­: • The frequency of collisions between casein micelles increases dramatically • This causes micelles to aggregate at much lower levels of k-casein cleavage • End result: the nonezymatic phase is greatly accelerated: rennet clotting time Ø, cutting time Ø, and curd firmness ­

General rules of thumb • Cut curd at a consistent firmness (for moisture control) • Cut curd at a consistent time from rennet addition (for maintaining acidification schedule) • If necessary: – Add calcium chloride (up to 0.02% maximum) – adjust cutting time to hold cutting firmness constant – adjust starter usage to maintain target acidification schedule

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