Ripening and packaging

Ripening processes: chemical and physical changes

Cheese ripening is basically about the breakdown of proteins, lipids and carbohydrates (acids and sugars) which releases flavour compounds and modifies cheese texture. The biochemical and biophysical processes involved have only partly been elucidated. Here we include only a few practical principles of ripening.

General Principles

  • Ripening varies from nil for fresh cheese to 5 years for some hard ripened cheese. Like a good wine, a good aged cheese should get better and better with age.
  • Ripening processes are broadly classified as interior and surface ripened.
    • Cheese which depend mainly on interior ripening (most hard ripened cheese such as Cheddar and Italian types) may be ripened with rind formation or may be film wrapped before curing. Having said that, I hasten to add, that traditional Italian types are always rind ripened. Cheddar and American varieties are the only ripened cheeses which (in my view) are not drastically altered by film wrapped curing.
    • Cheese which depend mainly on surface ripening include smear ripened and mould ripened
  • In the broadest terms 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.
  • Flavour and texture development are strongly dependent on:
    • pH profile
    • Composition
    • Salting
    • Temperature
    • Humidity
    • EXPERIENCE.
  • As a general rule factors which increase the rate of ripening increase the risk of off flavour development, and reduce the period of time when the cheese is saleable.

Protein Breakdown (Proteolysis)

Natural degradation of protein is called 'putrefaction' and results in 'rotten potato' type odours, especially if high quality proteins such as animal proteins are involved. That's because animal proteins contain the essential sulfur amino acids. These 'putrefactive' components are also the stuff of which good flavours are made. Protein degradation during cheese curing is a directed process resulting in protein fragments with desirable flavours.

  • Some off flavours associated with undesirable or excessive protein breakdown in cheese are bitter, stringent, putrid and brothy.
  • Protein breakdown causes shorter body which is less rubbery, less elastic, more meltable. 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. For example, bitter and brothy flavoured peptides are well known to occur in cheese.
    • 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)

Dairy fat is a wonderfully rich source of flavours, because it contains an extremely diverse selection of fatty acids. In particular, butter fat is the only natural fat which is rich in short chain fatty acids. Butyric acid for example is a potent flavour compound. As with all potent flavours the trick is to add just the right amounts in balance with other flavours. Here are a few principles:

  • Dairy fat without any ripening during cheese making is an important contributor to cheese flavour and texture:
    • Fresh dairy fat has the well known 'buttery' flavour associated with extremely low levels of free fatty acids.
    • Fat also 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.
    • Finally, fat is an important component of cheese softening and melting.
  • 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 generally quite lipolytic

Lactose

Milk contains no starch or fibre or any sugar other than lactose so all carbohydrate compounds in cheese are derived from lactose or produced by microorganisms. Relative to fat and protein lactose contributions to flavour are minimal. Here's a few principles:

  • At Day 1 following cheese manufacture most of the milk sugar has been removed in the whey by or by fermentation, that is converted to lactic acid by the cultures.
  • Residual lactose depends on the type of cheese and other factors. For examples:
    • High salt in the moisture phase of Cheddar slows lactose metabolism so lactose content is .3 to .7%% at one day after manufacture and slowly declines to less than 0.1%.
    • Residual lactose in Camembert cheese is used by Penicillium camemberti so it decreases quickly, especially on the surface, when the mould begins to grow.
    • In well drained cheese such as Swiss types, lactose is completely used up in a few hours.
    • In washed cheese varieties, lactose not leached by washing is quickly used up by the culture, especially for Dutch type cheese where salting is delayed. In Colby, early vat salting reduces the rate of utilization of residual lactose.
  • Many organisms, including yeasts and moulds in mould and smear ripened cheeses utilize lactate and produce various flavourful compounds.
  • Calcium salts of lactic acid may form white precipitates on the surface of aged cheese.

Principal Ripening Agents

Milk Enzymes 

  • Plasmin: A milk protease which survives pasteurization and breaks down caseins during cheese ripening.
    • Particularly important in Swiss type cheese.
    • Inhibited by Beta-lactoglobulin, so it has minimal activity in cheese made from ultrafiltered milk.
  • Lipoprotein lipase is the principal milk lipase
    • Inactivated by low heat treatment but is important to flavour development in raw milk cheese

Milk Coagulant

  • Each milk coagulant has its own proteolytic profile (see section on coagulants).
  • Purified extracts produce more consistent flavours but lack character.
  • For aged cheese no enzyme other than calf rennet and recombinant calf rennet has proven fully acceptable.
  • Rennet and recombinant rennet actively break down alpha-casein but do not break down beta-casein in cheese.

Lactic Cultures

  • During the early days and weeks of ripening, LAB numbers decrease while the numbers of nonstarter bacteria decrease. For example, in Cheddar cheese, LAB counts reach a maximum (up to 500 million per gram) within 3-4 days and then decrease to about 20 million at 4 weeks. However, the dying cells release enzymes which continue to ripen the cheese.
  • 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 small 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

Non-starter Microorganisms

Microorganisms present in the milk due to environmental contamination are important contributors to milk ripening. Some important facts are:

  • Bulk cooling and storage of raw milk selects for cold tolerant (psychrotrophic) bacteria (see Process and quality control procedures).
  • Heat treatment selects for thermal stable spore forming bacteria
  • Non-starter bacteria commonly present in heat-treat Cheddar include Lactobacillus sp. and Pediococci sp.
  • Many other bacteria and yeasts may be present and may or not grow depending on complex symbiotic relationships with other bacteria.
  • Heat treat is really a process of standardizing the nonstarter microorganisms, namely, eliminate proteolytic psychrotrophic bacteria but retain a range of useful ripening microbial agents.
  • Non-starter bacteria in cheese milk can be reduced by microfiltration.

Added Ripening Agents

Addition of lipases as noted earlier is common for Italian and other cheese varieties. The principal areas of continuing development are:

  • Accelerated ripening agents for all ripened cheese, especially Cheddar
  • Ripening agents for low fat cheese, again especially Cheddar.
  • The principal approaches are:
    • Direct addition of single enzymes of dairy or non-dairy sources
    • Enzyme cocktails which are mixtures of proteases and lipases. Other than in the preparation of enzyme modified cheese pastes, enzyme cocktails have had limited commercial success.
    • Enzyme capsules which release trapped enzymes during ripening.
    • Attenuated (freeze shocked or heat shocked) proteolytic cultures
    • Genetically modified cultures hold lots of promise for future success.
    • Culture adjuncts such as Lactobacillus helveticus in Cheddar cheese hold much promise to replace the normal diverse microflora of raw milk.

Cheese Composition for Optimal Curing

Cheese composition is critical to yield optimization, and both flavour and texture development. This section gives some detail on several critical composition parameters, with special reference to Cheddar cheese. New Zealand export Cheddar cheese is all graded by composition analysis as indicated in Figure A on the right. Figure B on the right indicates the ranges which are typical of good Canadian Cheddar.

MNFS

  • Moisture: higher moisture means faster ripening which means more potential for off flavours and over ripening.
  • water activity (aw) decreases with age because ripening results in many soluble breakdown products of acids, sugars, proteins and lipids
  • fresh Cheddar aw = 0.98 which is conducive to most bacteria
  • aged Cheddar aw as low as 0.88 which is too low for most bacteria
  • MNFS is a better index of cheese ripening potential than % moisture
  • Optimum MNFS depends on expected date of maturity and curing temperatures:

examples for Cheddar: 100C, 6-7 months MNFS = 53%

100C, 3-4 months MNFS = 56%

  • MNFS is controlled mainly by pH at dipping and cooking treatments. Subsequent curd treatment such as cheddaring and salting also influence MNFS
  • MNFS is also influenced by FDM. Other conditions being kept constant, MNFS increases with increasing FDM, because fat inhibits syneresis.

S/M

  • Determines rate of acid development during pressing and early curing and, therefore, influences the minimum pH
  • Affects bacterial profile, eg., high S/M will discourage contaminating bacteria such as coliforms.
  • Critical to rate of proteolysis and the type of protein derived flavours
  • Acceptable range is broad (3.6 - 6.0), fortunately because S/M varies widely even within a single cheese.
  • Salt uptake is affected by quantity of added salt, size of curds, moisture content of curds, and acidity

FDM

  • Higher fat restricts syneresis, so MNFS tends to increase with FDM
  • Fat shortens and softens cheese texture because the fat globules physically disrupt the protein matrix.
  • Adjusted by milk P/F (See Treatment of milk for cheese making)

pH

  • The pH profile is the single most important trouble shooting tool. Critical points are: cutting, draining, milling, 1 day and 7 days
  • Most cheese including Cheddar should reach a minimum pH of 5.0 to 5.1 during the first week after manufacture; obtaining a final pH in this range is greatly helped by increased buffer capacity of milk proteins in the pH range 5.4 - 4.8.
  • Factors determining the pH at one day are amount of culture, draining pH, washing, curd treatment such as cheddaring and salting.
  • Draining pH is most important to cheese texture and also determines residual amounts of chymosin and plasmin in the cheese.
  • pH increases with age due to release of alkaline protein fragments. This is especially true of mould ripened cheeses. Camembert pH increases from 4.6 to 7.0, especially on the surface.
  • Increasing pH during curing encourages activity of both proteases and lipases.

Temperature of Curing

  • Cheddar types: 4 - 10C, 8-10C is the recommended range. It is desirable to initiate ripening for several weeks at 4-6C and then increase the temperature to 8 - 10C. Low temperature initially, minimizes early growth of starter and non-starter bacteria and reduces the risk of too rapid ripening and off flavour development. It also minimizes the risk of the minimum pH reaching levels 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

Surface ripened cheese also 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 to the type of surface characteristics, cheese treatments are grouped 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 and Oka
  • Dry rinds which may be coated with oil or butter to prevent cracking and desiccation, e.g., Edam, Scamorza, and 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., 640 lb 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.