Wiki: Microorganisms & Cheese Making

This Wiki Article provides an introduction to microorganisms common in cheese making. Microorganisms are organisms that are unicellular or live in a colony of cellular organisms such as bacteria, fungi, archaea, and protists; microscopic plants (green algae); and animals such as plankton and the planarian. Microorganisms were the first forms of life to develop on Earth, approximately 3–4 billion years ago, the study of microorganisms is called microbiology.

Microorganisms live in all parts of the earth’s biosphere where there is liquid water, including soil, hot springs, on the ocean floor, high in the atmosphere and deep inside rocks within the Earth’s crust. Microorganisms are critical to nutrient recycling in ecosystems as they act as decomposers. Microorganisms are present in raw milk and are used in controlling the fermentation process in making cheese, either natively or by additionally applying, and are critical in developing different cheese types flavours and aromas, and in inhibiting undesirable organisms. Microorganisms are also used in brewing, winemaking, baking, pickling and other food making processes. Historically and in many cases currently cheese has been made in very rustic facilities with many ambient/wild microorganisms, which does not necessarily mean unsanitary, but does result in cheese quality that is too inconsistent for modern cheese factories but good for home and artisan cheese making.

The main types of microorganisms used in making cheese are shown below.

Bacteria

Bacteria are a biological kingdom of simple single-celled, prokaryote (lacking a cell nucleus) microorganisms. They are typically a few micrometres in length and have a wide range of shapes ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat, growing in water, soil, acidic hot springs, as well as in organic matter and the live bodies of plants and animals including humans. There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water; and in total form a bacteria with a biomass which exceeds that of all plants and animals. There are approximately ten times as many bacterial cells in the human flora as there are cells in the human body, large numbers of bacteria are on the skin and in the intestines. Bacteria are vital in recycling nutrients, however most bacteria have not been characterised, the study of bacteria is known as bacteriology, a branch of microbiology.

Bacteria reproduce asexually by simple division of the cell and its contents, called fission. The doubling time can be as short as 20 min, and as each cell grows and divides at the same rate as the parent cell, this could under favourable conditions translate to an increase from one to 10 million cells in 11 hours. However, bacterial growth in reality is limited by lack of nutrients, accumulation of toxins and metabolic wastes, unfavourable temperatures and dessication. Bacterial populations are expressed as colony forming units (CFU) per gram or millilitre.

Bacterial growth generally has several phases:

  • Lag Phase: Time for bacteria to become accustomed to their new environment. There is little or no growth during this phase.
  • Log Phase: Bacteria exponential growth begins; the rate of multiplication is the most rapid and constant.
  • Stationary Phase: Rate of multiplication slows down due to lack of nutrients and build-up of toxins. At the same time, bacteria are constantly dying so the numbers actually remain constant.
  • Death Phase: Cell numbers decrease as growth stops and existing cells die off.

Milk is sterile at secretion into the udder but is contaminated by bacteria before it leaves the udder. Except in the case of mastitis, the natural microflora of bacteria at this point are harmless and few in number. Further infection of the milk by microorganisms can take place during milking, handling, storage, and other pre-processing activities. If significant lactic acid producing bacteria are in raw milk, it will, with time and warmer temperatures, multiply, acidify and curdle the milk (commonly called clabber) after which whey can be drained. However, depending on bacteria amount and types this can result in either inefficient, uncontrollable, and unpredictable and thus variable results and if lactic acid producing bacteria are minimal, an environment for unwanted/unhealthy bacteria to reproduce. Thus to extend shelf life, milk is commonly pasteurized to kill off most of the bacteria, both good and bad types. Commonly in cheese making, wanted lactic acid producing bacteria are added (inoculation) to the milk, to out-compete unwanted native bacteria, these are called starter cultures.

Common bacteria used in making cheese are:

  • Lactic Acid Producing Bacteria: Commonly called starter cultures, naturally in milk but commonly added to milk to ferment lactose in milk to lactic acid causing coagulation and release of whey to condense remaining milk ingredients into cheese for longer shelf life.
  • Brevibacterium linens which is ubiquitously present on the human skin where it causes foot odor and applied to give cheese rinds an orange colour and a very pungent aroma, examples are Limburger and Port-du-Salut.

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Fungi

In biological terms, Fungi are a Kingdom and thus different from other Kingdoms such as plants, animals, and bacteria. Fungi are made up of yeasts, molds (spelt moulds in Britain) and mushrooms. The discipline of the study of fungi is called mycology, a branch of microbiology. Fungi are abundant worldwide but most are inconspicuous because of the small size of their structures. They may become noticeable when fruiting, either as mushrooms or molds. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange. Fungi have long been used as a direct source of food, such as mushrooms and truffles as a leavening agent for bread, and in fermentation of various food products, such as wine, beer, soy sauce, and cheese.

Little is known of the true biodiversity of the Fungi Kingdom, which has been estimated at around 1.5 million species, with about 5% of these having been formally classified. Most fungi grow in cylindrical, thread-like structures 2–10 µm in diameter and up to several centimeters in length called hyphae. From these they grow by a combination of apical growth and branching/forking resulting in mycelium, an interconnected network of hyphae which is normally more visible to the naked eye, (ie fuzzy mold on damp walls, spoiled food such as bread, or on cheese where used to provide flavour and aroma.

Yeast Fungi

Currently yeasts are thought to be about 1% of all fungal species, about 500 have been described by mycologists. Yeasts ferment carbohydrates to carbon dioxide and alcohols, and are common in baking such as bread making for their carbon dioxide forming attributes and in for their alcohol making attributes in alcoholic beverage making such as beer and wine.

Yeasts are intentionally used in making some cheese types to enable rind development and are also a source of unwanted “infections” resulting in rising bread/beer yeasty smells and swelling. Note that Swiss types cheeses with eyes (Emmenthaler, Leerdammer) are not made with yeast but with Propionibacterium freudenreichii, a bacteria.

Mold Fungi

Molds grow like mushrooms, they have a surface component and send down roots called mycelia into the insides of the cheese where they break down the fats and proteins and create different flavors and textures, some penetrate just cheese rinds, some penetrate the whole paste (for example Brie or Camembert.

Common molds used in making cheese are

  • Geotrichum.
  • Penicillium white strains used in making the fluffy coating on Brie/Camembert.
  • Penicillium blue strains used in giving blue cheeses such as Roquefort and Stilton their distinctive blue to blue-green veins.

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Wiki: Turning Cheeses

Turning gravity whey draining Camembert hoops, quick lift - turn - drop like turning a pancake.

This Wiki Article discusses the practice of turning or flipping a cheese normally upside down, which occurs at several cheese making steps depending on cheese type and recipe. Soft non-formed cheeses like yogurt and cream cheese are not turned. While a relatively simple subject there are some best procedures which if not followed can result in damage or defects to the cheese.

For all the Descriptions, Reasons, Methods, and Frequencies detailed below i) keep records for next cheese make of same cheese type, and ii) do not “sweat” attaining the exact time to turn, high accuracy is not critical. 

Turning Unpressed Cheeses During Forming

Turning gravity whey draining Camembert hoops, quick lift - turn - drop like turning a pancake.
Turning gravity whey draining Camembert hoops, quick lift - turn - drop like turning a pancake.

Description

Soft formed cheeses such as when making Camembert, Feta, or Ricotta are normally turned during draining in unpressed type mold or hoop.

Reason

To enable gravity to provide:

  • An evenly shaped versus lopsided shaped cheese for proper development and for better aesthetics.
  • Even moisture, fat, and protein distribution throughout the cheese and thus proper development of the cheese.

Method

  1. If using unpressed draining mold such as for Ricotta or Feta making, then turn mold upside down and catch cheese in hand and then drop cheese back into the mold but top down, turned.
  2. If using hoops such as for Camembert making, to hold curds together and avoid cheese going lopsided, place second mat over top of hoop, hold mat-hoop-mat sandwich with both hands, then lift quickly into air, then cheese is “weightless”, quickly turn the cheese then lower and allow cheese to slide down inside hoop. Similar to single handed flipping a pancake in a frying pan.

For both methods, initially on first turn the cheese will be soft and poorly formed but will gain firmer shape as drained further.

Frequency

If no turning schedule in recipe then turn after ½ hour, 1 hour, 2 hours, 5 hours, 12 hours, 24 hours, 3 days, etc.

Turning During Brine Bathing Cheeses

1 kg Havarti #1, Surface Stress Crack From Improper Top Pinch Lifting By Hand Out Of Brine - CheeseForum.org
1 kg Havarti #1, Surface Stress Crack From Improper Top Pinch Lifting By Hand Out Of Brine - CheeseForum.org

Description

Some cheese making recipes such as Gouda’s use brine bathing as a method salting cheeses and building a dehydrated hard rind as protection against surface molds. Cheeses during brining are periodically turned.

Reason

As cheese is less dense than brine, during brining the cheese floats with the top above the surface of the brine similar to an iceberg where 10% is above the surface and 90% is in the sea. Here the cheese should be periodically turned to ensure even brining and thus even rind development of all surfaces.

Method

The easiest is to push cheese down into the brine and turn under the brine before resurfacing. Cheeses can also be lifted up out of the brine and turned and replaced into the brine, but if done they should be lifted from the bottom and thus placed in compression as pinching the top of a cheese to lift it can result in tears in the oft young cheese as it weak in tension.

Frequency

If no turning schedule in recipe then if brine bathing for days, turn minimum every half day, if small ~2 pound/1 kg cheeses and brining for few hours, then turn every hour.

Turning Cheeses During Pressing

Description

 

Reason

 

Method

As cheese is moist and weak in tension yet strong in compression, lift cheese from bottom and turn with hands, do not pinch and lift vertically as cheese is weak in tension and can crack.

Frequency

If no turning schedule in recipe then turn after 1/2 hour, 2 hours, 4 hours, 8 hours, 1 day, etc depending on duration of pressing.

Turning Cheeses During Air Drying And Aging

Description

Cheeses after forming are commonly air dried and then aged during which the cheeses are turned, common examples are Gouda and Edam.

Reason

The reasons for turning formed cheeses during air drying and aging are to:

  • During air drying to allow all surfaces of the cheese in early aging days to dry evenly and to minimize the cheese having a damp bottom and high risk of yeast infection developing on the bottom against the draining mat or board.
  • During aging to minimize gravity causing a lopsided pear shaped cheese resulting in:
    • Uneven moisture, fat, and protein distribution throughout the cheese and improper development of the cheese.
    • Aesthetically unpleasing cheese.

Method

When young and cheese is moist, as strong in compression, lift cheese from bottom and turn with hands, do not pinch and lift vertically as cheese is weak in tension and can crack. As cheese ages and looses moisture it generally has more tensile strength and can withstand more robust handling.

Frequency

If no turning schedule in recipe then turn after 2 hours, 6 hours, 12 hours, 24 hours, 3 days, 1 week etc.

Wiki: Dry Salting Rinds

Four 10 cm diameter Camemberts after dry salting.

This Wiki Article discusses dry salting cheese rinds, a procedure normally performed after forming the cheese and before air drying and aging. This salting method is commonly used with mold ripened cheeses such as Camembert & Brie and with washed-rind type cheeses. 

For the dry salt to be absorbed by the formed cheese, it must first dissolve and form a brine at the cheese’s surface after which it then diffuses into the cheese. As reviewed in the Wiki: Salt’s Function article, the % salt content in the type of cheese being made is critical. Thus it is important to understand the six main factors that control this method of salting cheese. 

Ambient Humidity

Soft rind dry salted type cheeses, are aged in high ~95% ambient humidity environment after dry salting. The high humidity is to prevent excessive evaporation of moisture from the surface of the cheese which would result in a dehydrated dense and tough rind being formed. Further these cheese types normally must remain with a high moisture content at their surface to enable their surface growth of molds, yeasts, and bacteria and in time their growth into the center of the cheese. 

For hard rinded cheeses, the ambient humidity is held relatively low @ 85% to encourage expelled whey to be evaporated resulting in a dehydrated surface layer of cheese, the start of the rind development process. Repeated applications of dry salt to hard rinded cheeses result in a steadily increasing dehydrated layer. 

Cheese Size

Four 10 cm diameter Camemberts after dry salting.
Four 10 cm diameter Camemberts after dry salting.

Generally, the cheese making procedure dictates the size of the formed cheese (good examples are generally uniform sized Camembert’s and Brie’s), and thus the procedures amount and method of applying the salt is matched to the size. 

However, if deviating in size of cheese, consideration should be given to the number of applications of dry salt and thus also the time to allow the cheese to reach it’s salt % content target range. 

Note, for large cheeses this becomes a problem because in time the build up of a dense hard layer from repeated dry salting the cheese’s surface will inhibit further salty brine uptake into the cheese and the dry salt will no longer be absorbed resulting in a cheese with sub-optimal % salt content. It is for this reason that large rinded wheels of cheese are often brine salted first, and then their rinds dry salted to i) reach the target % salt content and ii) to develop their hard rinds. 

Cheese Temperature

As with dry salting curds, the temperature of the cheese will be a controlling factor of the salt’s absorption rate. However their is ample time to absorb the salt while the fresh cheese is drying so this is not normally an issue and thus the temperature during dry salting more a function of the cheese’s drying and aging requirements. 

Salt Type

Standard sodium chloride, NaCl salt is used. It should be coarse granular sized rather than very fine to slow down the speed of dissolving into brine and absorption into the cheese. As with high temperatures, fine salt can result in a rapid flush of whey and fat which can wash away other salt before being absorbed resulting in incorrect salt % content of the cheese type being made. Different types of salt are discussed in the Wiki: Salt Types article. 

Salt Amount

As reviewed in the Wiki: Salt’s Function article, final salt content of the cheese type you are making is critical. Thus follow the cheese making procedure accurately on amount/weight of salt being applied versus weight of final cheese(s). If making several cheeses such as Camemberts in one make, ensure salt is allocated evenly. 

Salt Application

There are two salt application methods for dry salting rind cheeses: 

  1. For soft rind type cheeses, sprinkle measured amount of dry salt onto the whole rind including sides. Care should be taken to ensure the salt does not land off the cheese otherwise sub-optimal % slat content will be obtained.
  2. For hard rind type cheeses, rub dry salt onto the rind.

Wiki: Pressing Cheeses

Two 1.5-2 kg final cheese weight Kadova brand Gouda shaped pressing molds with formed mesh nets and mesh lined followers.

This article discusses pressing cheeses which is primarily performed on rennet coagulated lower moisture content aged cheeses after curds are prepared, (steps dependent on cheese type being made). Many cheeses have whey drained by gravity either by hanging the prepared curds in cheese cloth or by placing in a mold, these are not discussed in this article. Pressed cheese are in general pressed by placing the prepared curds in a cheese cloth lined hoop, on top of a draining mat, then placing a follower on top of the curds and then placing weights on top of the follower.

Pressing Goals

0.5 kg Gouda cheese pressing in homemade hoop and cloth bag shaped liner, expelled whey needs to be drained.
0.5 kg Gouda cheese pressing in homemade hoop and cloth bag shaped liner, expelled whey needs to be drained.

The goals of pressing the prepared curds are to:

  • Reform a large cheese shaped drier curd, normally without any voids.
  • To dehydrate the curd at the surface and form a tough rind that is less susceptible to unwanted micro-organisms.
  • To knit the curds into a homogeneous cheese.

Some cheeses when manufactured in large wheels such as Stilton are not externally pressed, but are effectively pressed under their own weight. Making smaller artisan or hobby sized wheels of these cheeses often requires light pressing. Some cheeses such as washed curd Gouda’s need only light pressure versus some like cheddar require high pressure to form a knit. However, Dutch cheese makers of old pressed their large wheels with high pressures not to form a knit but to form a very dry and hard environmentally resistant rind as they had poor control of the weather and thus poor control of their aging environment.

Hoops & Molds

In gravity draining whey from cheese, commonly a thin mold or hoop and mats are used. In pressed cheeses the form is often called a hoop as it was historically in the shape of a round hoop as that shape was better to withstand the sometimes high hoop stresses from the applied weights.

Inside a cloth liner was placed inside the hoop in hold the initially moist and soft curds, but modern manufacturing has enabled more heavy-duty mold type devices with integrated bottoms and form fitted mesh liners and lids.

Pressing Method

Two 1.5-2 kg final cheese weight Kadova brand Gouda shaped pressing molds with formed mesh nets and mesh lined followers.
Two 1.5-2 kg final cheese weight Kadova brand Gouda shaped pressing molds with formed mesh nets and mesh lined followers.

The following is the standard method for pressing cheeses, it will vary depending on hoop or mold type and on cheese type.

  1. A hoop, commonly with small holes to enable whey expulsion is placed on some sort of mat that additionally allows whey to flow out of the bottom of the cheese.
  2. Inside the hoop a cloth is placed to initially hold the curds so that they aren’t extruded out the holes.
  3. The prepared curds are placed in the cloth and a round disk-shaped “follower” placed on top of the curds.
  4. While pushing down on the follower, the cloth is pulled up straight all the way around the sides to minimize wrinkle-fold lines in the sides of the cheese.
  5. Initially a light weight is applied on top of follower to apply a light pressure. Going light at first gives the excess whey in the interior time to move out of the cheese before the curds at the edge are dehydrated effectively sealing the whey inside the cheese, a location for unwanted micro-organisms to grow. If heavy weight/high pressure was applied initially then i) the fresh very soft curd can be extruded up around the follower or out of weep holes if no liner is used, and ii) the curds at the surface would rapidly dehydrate forming a barrier to further whey expulsion.
  6. After a short period, the very sort formed single curd is removed from the cloth and turned and replaced. Again while pushing down on the follower pull the cloth up verticlly aroound the circumference of the formed curd and then apply a heavier pressure. This is to i) enable the previously top of cheese to also form a slightly dehydrated layer and ii) enable a more uniform shaped and moisture content cheese to be created, iii) to minimize the curds impregnating and sticking to the cloth, and iv) to minimize cloth wrinkle-fold lines on side of the forming cheese.
  7. The above step is repeated with steadily longer times between turnings and with steadily higher pressures, depending on the cheese type and recipe-procedure.

Notes:

  • Some cheese makers only use the cloth lining for the initial light pressings to minimize the cloth imprint around the sides of the cylinder during higher pressure pressings.
  • Some cloths are sewn to snuggly fit the inside of the hoop and thereby reduce ridge lines around the periphery of the cheese.

Presses

Final pressing two 4 lb Gouda's in Kadova Brand molds using stepladder and large bucket of paint as weights.
Final pressing two 4 lb Gouda's in Kadova Brand molds using stepladder and large bucket of paint as weights.

Presses range from the simple improvised (exercise hand weight, jugs of water, step-ladder balanced one end on the hoop) to highly leveraged or geared machines to modern pneumatic (air powered) machines and are the subject of a future separate article.

Tricks & Traps

Common tricks and traps in pressing cheeses are:

  • Sticking of the curds to the cheesecloth of hoops or to the mesh liner in some molds, this normally occurs when the curds pH is too low or when the weave is too coarse and the pressed curds are imbedded into the cloth. Solutions are to turn the cheese a few times in the first couple of hours to build up a good rind, use a tighter weave, and additionally if required to soak the cloth or nets with warm whey with addition of Calcium Chloride (warmth helps curds to knit) or to spray with a salt/vinegar/CaCl2 solution. If required the cloth liner can be additionally sprayed between cheese turnings while in the press.