Factors effecting quality in cheesemaking

LJW 2009 BUA/HAUC

AP&P

Milk quality

Composition Fat - % in milk effects yield ,fatty acid profile

effects flavours , texture + melting point - spoilage reactions (1) break down of the triglyceride fat structure

releasing fatty acids such as butyric to create a rancid flavor

(2) oxidation of unsaturated fats creating an ‘off’ flavour (cardboard )

Milk quality

Proteins – Caseins + whey proteins , caseins critical to process , whey proteins are a ‘waste’ product

• Alpha-S1 casein - 33% (binds calcium strongly + sensitive to break down by rennet )• Kappa-casein - 11% (stabilizes casein particles

against coagulation + bonds with whey proteins during heating )

Lactose – the fermenting agent for the starter culture , constant in milk @3.6%

Milk Quality cont. Hygienic quality a) Spoilage organisms – Proteolytic bacteria - cause bitterness and putrefaction : Pseudomonas which are

psychrotrophic and produce heat stable lipases + Bacillus which form heat stable spores and survive pasteurization

Lipolytic bacteria - degrade fats and produce lipolytic rancidity : Several psychrotrophic species of Pseudomonas produce heat stable lipases as well as proteases.

Gas producing microorganisms which cause cheese openness, floating curd in cottage cheese, and gassy milk.

Yeasts are common contaminants during the cheese making process. They may cause 'yeast slits' in cheese and contribute to ripening of surface ripened cheese.

Coliforms ( non pathogenic) are always present in milk but should be out competed by the rapidly growing starter culture .

Clostridium tyrobutyricum – is thermoduric + spore forming causing gas formation (carbon dioxide) during the later stages of ripening of Swiss and Dutch type cheeses.Only 500 spores /l milk will cause late gas defect.

(Propioni bacterium produces the desirable gas formation in Swiss type cheese)

Hygienic quality cont.Ropy bacteria cause stringy milk - eg Alcaligenes viscolactisSweet curdling bacteria produce rennet-like enzymes which may coagulate milk. eg

Bacillus subtilis and Bacillus cereus.

b) Pathogenic organisms – heat sensitive organisms should be removed by pasteurisation Surviving thermodurics might include – some strains of Bacillus cereus Listeria monocytogenes –a marginal survivor of pasteurisation - acid tolerant

psychotroph Cheese made from unpasteurised milks are exposed to the full range of spoilage and

pathogenic bacteria present in milk and rely on very high standards in production + the ‘hurdles’ to bacterial growth inherent in the cheese making process

c) Antibiotics – starter cultures are very susceptible to antibiotic contamination - will result in starter and cheese making failure

Hygienic Quality cont.d) Mastitis – effects cheese making in 2 areas ; (i) During production - Mastitic milk contains more plasmin, a

heat stable milk protease which degrades protein and causes more protein to be lost in the whey.

Reduced casein directly affects cheese yield + poor curd formation adds to yield loss

(ii) Cheese quality - Soft, less elastic, sticky and grainy cheese texture. Increased flavour intensity, usually with off flavours

Bacteriophage in starter cultures Bacteriophage (bacterial viruses) - parasites, ( part of their life cycle is dependent

on the host bacteria.)

Basic life cycle (lytic cycle): Phage attaches itself to the bacterial cell wall by its tail, bores a hole in the wall

with the help of enzymes and injects its DNA into the cell. The protein sheath remains outside the cell.

From the moment of invasion the bacteria begins to reproduce phage DNA and protein in addition to its own.

Nucleic acid and protein strands assemble themselves into new phage particles which eventually lyse the cell (break it open) to release the phage particles into the medium. A new generation of phage are now available to repeat the cycle

Culture growth will stop when phage levels reach 103 to 107 per ml.

Bacteriophage – cont. Phage reproduce quickly -every 30 to 50 min and each lysed cell will release

50 to 100 new phage. Phage are quite strain specific which is the reason for culture rotation. As

many as 10 different cultures may be rotated on a daily basis. Culture failure due to phage can be recognized by normal acid development

initially followed by a decrease or termination of culture growth at a later stage.

This is different than inhibition due to antibiotics which can be recognized by no or slow initial growth; if inhibition is not severe, culture growth and acid development by resistant strains or mutants may increase with time.

Summary of phage control measures

• Use aseptic techniques with proper culture room. • Rotate cultures daily and/or use defined phage resistant strains. • Use phage resistant media for culture preparation. • Use direct-to-vat culture to avoid contamination during

transfers. • Use a mixed strain culture of two closely related strains. • Remove and dispose of whey daily • Routinely check for presence of phage using a culture activity

test with the culture currently in use and some whey from the most recent vat

Stirring

Ripening /Maturation

Cheese ripening is basically the breakdown of proteins, lipids and carbohydrates (acids and sugars) which releases flavour compounds and modifies cheese texture.

Ripening processes are broadly classified as interior and surface ripened.

• Flavour and texture development are strongly dependent on: – pH profile – Composition – Salting – Temperature – Humidity – Cheesemakers skills / experience.

• There are three sources of cheese flavour: – Flavours present in the original cheese milk, such

as natural butter fat flavour and feed flavour. – Breakdown products of milk proteins, fats and

sugars which are released by microbial enzymes, enzymes endogenous to milk, and enzyme additives.

– Metabolites of starter bacteria and other microorganisms. These include products from catabolism of proteins, fats and sugars

Protein Breakdown (Proteolysis)

Natural degradation - 'putrefaction‘ especially in high quality /animal proteins containing sulphur A/As

Protein degradation during cheese curing is a desirable / directed process• Protein breakdown causes ‘shorter’ texture - less rubbery/ elastic, more

meltable cheese For example, flavour and texture development in Cheddar are mainly dependent on

protein breakdown and much less dependent on fat breakdown. • Protein breakdown involves three general types of processes:

– Proteases break proteins into smaller peptides, some of which are flavour compounds– Peptidases further break down peptides to amino acids. – Further catabolism of amino acids by cheese microorganisms produces aldehydes,

alchohols, carboxlic acids and sulfur compounds, many of which are flavourful. • The amino acid, tyrosine, forms crystals in aged cheese such as Parmaggiano

regiano, which are readily detected on the palate.

Fat Breakdown (Lipolysis)

Milk fat is a wide source of flavours, as it contains a diverse selection of fatty acids –particularly short chain fatty acids.

Butyric acid ( buttery) is a strong flavour compound.

– Milk Fat acts as a flavour reservoir, so hydrophobic (fat soluble) flavours derived from protein breakdown are stored in the fat and released during mastication in the mouth.

– The state of fat in a cheese is an important component of its melting qualities . • The fat derived flavours associated with cheese ripening result from the

release of fatty acids by lipolysis and further modification of fatty acids by microorganisms to other compounds.

• Varieties traditionally made from goats' milk have higher levels of lipolysis.

• Blue moulds are lipolytic and add to the modification of fats

Lactose

Relative to fat and protein - lactose contributions to flavour are minimal -

Fermentation by the starter culture removes most of the lactose ( converted to lactic acid) , some is lost in whey

However - many organisms, including yeasts and moulds in mould and smear ripened cheeses utilize lactate and produce various flavourful compounds.

Principal Ripening AgentsMilk Enzymes• Plasmin: A milk protease which survives pasteurization and breaks down caseins during cheese ripening. Particularly

important in Swiss type cheeses. Milk Coagulant ( rennet) • Each milk coagulant has its own proteolytic profile (see section on coagulants). • For aged cheese only rennets ( animal or GM) have proven success . Starter Cultures• Lactic cultures contribute to proteolysed flavours but are minimally lipolytic • Heterofermentative cultures ferment citrate as well as lactose and contribute both flavour (diacetyl) and carbon dioxide for

‘mouse hole’ / ’ eye’ development Secondary Cultures• In Swiss types, carbon dioxide production by Propionibacterium is encouraged by exposure to 200C for about 3 weeks after

brining and drying off in the cold room. • For smear ripened cheese, Brevibacterium linens , coryneform bacteria, and yeasts are encouraged by high humidity (90-

95%) and washing to discourage moulds • Penicillium sp. for Camembert, Brie and Blue types require 85-90% humidity and air circulation to provide oxygen

Ripening Conditions

Cheddar types: 8-10⁰c recommended ( lower initially to minimise off flavour development + pH falling below 5.0)

• Most European varieties are stored at 10 - 15C for initial ripening and then 4C until consumed.

• Surface ripened varieties are ripened at 11 - 15C.

Humidity of curing/ripening

Surface ripened cheese require adequate air circulation to provide sufficient oxygen for moulds and yeasts. Humidity requirements in general are:

• Washed bacterial surface ripened: 90-95% • Fungal flora: 85-90% • Dry rinds: 80-85

Ripening Treatments

According surface characteristics, treatments are as follows:• Ripened by surface moulds • Washed rinds with out (or with little) bacterial growth, e.g., St. Paulin types. • Washed rinds with smear, e.g., Muenster types• Dry rinds which may be coated with oil or butter to prevent cracking and desiccation, e.g.,

Edam, Parmesan. • Waxes and resins which may be applied by dipping, brushing or spraying. These provide good

protection but are more permeable than plastic films, so it is still desirable to maintain 85% RH to prevent drying.

• Rindless cheese which are cured in moisture and gas impermeable film or in large blocks (eg., Cheddar)

Waxes and films may be treated with anti-mould agents such as pimaricin, sorbic acid and propionates to prevent mould growth.

Packaging

Vacuum and/or gas flush (N2 and CO2) in gas and moisture proof film are common. – Vacuum alone is not recommended because complete evacuation of oxygen

is difficult and small unsightly mould spots often appear. – Gas flush with CO2 or blends of CO2 and N2 effectively prevent mould growth.

• CO2 is water soluble so it is absorbed into the water of the cheese and the package becomes tight.

• N2 which is not water soluble is useful for applications, such as shredded cheese and cheese curd, where a loose package is desired.

• High density plastic (rigid containers) are used for fresh cheese such as cottage.

• Oxygen permeable wrap such as grease proof paper and foil-laminated but unsealed wraps, are preferred for surface ripened soft cheese

DEFECTS AND GRADING• Body – relates to ’form’

– Crumbly/short: often due to excess salt or acid – Corky: due to overcooking, low fat, low moisture, or excess salt. – Mealy: this defect is felt when massaging the cheese between the thumb and forefinger. It

is usually caused by excess acidity. – Pasty: sticks to the palate and fingers; due to excess moisture. – Weak: breaks down too quickly when worked by hand; due to excess fat or moisture.

• Texture relates to ‘openness’– Holes of irregular shape caused by trapped whey, considered a defect in Cheddar. – Gas holes(desirable in many types of cheese ) but as defects include:

• Early gas defects due to coliforms. These appear as small, sphericle, shiny holes. • Late gas due to Clostridium. tyrobutryricum or perfringens, especially in some European made

cheese. • Yeast slits due to yeast growth.

• Flavour. Most grading systems assign the greatest weight to flavour defects.

– Acidic flavour , causes are : • Too much moisture (i.e., too much lactose). • Too much starter (i.e., too much acid development before dipping). • Salting too late or too little. • Too warm during or immediately after pressing. • Fruity/Yeasty flavours are usually associated with high pH and bitterness, and sometimes with yeast

slits. • Unclean flavours may be associated with coliforms. • Whey taint is due to high moisture and is usually associated with acid defects including bitterness.

• Colour. Most important colour parameter is uniformity , graders do not evaluate colour intensity. : – Mottled: may be an acid defect or caused by mixing cheese from different vats. – Seamy: this is a Cheddar defect where the curd particles fail to knit properly. Causes are:

• Greasy curd from high temperature during pressing • Improper salting, too soon after milling or pH at salting is too high or too low • Hooped too soon after salting

Finish. There is a lot of art and patience required to produce cheese with a good finish. Common defects are:

Checked/Cracked: too dry on surface Greasy: temperature too high during pressing or curing Huffed: gassy

Surface mould is definitely one of the most common defects. Indeed a frequent question to me, is about the safety of eating mouldy cheese.

Unsymmetrical/Rough: poor workmanship

…….What to do with the Whey ?? …..