Wiki: Rennet

USA Old Kirk & Kirk Rennet Storage Bottle - CheeseForum.org

The roots of the term rennet come from rennet derived from animal parts, but in cheesemaking, with modern manufacturing the term is now used broadly to describe a range of chymosin and pepsin based coagulants. This general rennet article discusses formats, storage, amount, and preparation; specific rennet types, their formats and concentrations are in the Rennet Types, A To Z article.

USA Old Kirk & Kirk Rennet Storage Bottle - CheeseForum.org
USA Old Kirk & Kirk Rennet Storage Bottle - CheeseForum.org

Rennet through the ages has been made from the abomasum or fourth stomach, in young un-weaned milk fed calves and contains the rennet enzymes chymosin and pepsin. Due to high cost of manufacture and as calf based rennet does not qualify for some diets and may concern some for animal welfare reasons, starting in the 1990’s other forms of coagulants were manufactured.

Formats

Rennet normally is manufactured and available in a liquid, paste, and powder formats with liquid being the most common by far.

Storage

Most calf based based rennet manufactures recommend:

  1. For liquid calves rennet, store at temperature below 3-7C / 38-45F, i.e. in household fridge, not in normally warmer cheese cave. Store away from direct sunlight to preserve maximum activity (ultra-violet rays in sunlight destroy the rennet activity). Product’s strength will decline at 0.5% per month if ideal storage is followed for all times between manufacture and use.
  2. For powdered calves rennet, store at 38 to 45°F in closed container away from sunlight. This can give high, greater than 1 year shelf life.

Amount

Malaka Brand Vegetarian Liquid Rennet Drop Bottle - CheeseForum.org
Malaka Brand Vegetarian Liquid Rennet Drop Bottle - CheeseForum.org

As rennet can come in different strengths, any specified amount of rennet in a cheese making procedure should be ignored and the amount of rennet used per volume of milk based initially on the manufacturer’s directions. These directions can be found either on the product’s container or from their website (many of these files are posted in CheeseForum.org’s Library in the Forum). This amount should be increased or decreased with the users experience and results with the type of milk they are using.

Note:

  • Rennet degrades based on age and storage best practices, adjust as appropriate.
  • In general, store bought manufactured pasteurized and homogenized milk is requires more rennet than raw milk.

Preparation

  1. For single strength liquid calves rennet, dilute in cool un-chlorinated water at ratio of 15-20 parts water to 1 part rennet by volume.
  2. For powdered calves rennet, dissolve in 400 times it’s weight of non-chlorinated cool water, let sit for 30 minutes with occasional agitation for complete dissolution.
CHR Hansen Brand 75 liter Packages Of Powdered Microbial Fermented Fungus
CHR Hansen Brand 75 liter Packages Of Powdered Microbial Fermented Fungus

Wiki: Rennet Types

CHR Hansen Brand 75 liter Packages Of Powdered Microbial Fermented Fungus

The roots of the term rennet come from rennet derived from animal parts, but in cheesemaking, with modern manufacturing the term is now used broadly to describe a range of chymosin based coagulant. This specific rennet article reviews the different types chymosin based milk coagulants, general information on is in the Wiki: Rennet.

Animal Based

USA Old Kirk & Kirk Rennet Storage Bottle - CheeseForum.org
USA Old Kirk & Kirk Rennet Storage Bottle - CheeseForum.org

Animal based rennet is made from the abomasum of un-weaned milk fed calves. The abomasum is also known as the fourth stomach, and in young animals, the “rennet-bag” or “vell”. The tissue secretes acids and the rennet enzymes chymosin and pepsin. New-born calves have 95% chymosin (sometimes referred to as rennin) and 5% pepsin, as the animal ages and its diet changes from milk to grass, the ratio changes such that at about nine months of age, the ratio has reversed to 10% chymosin and 90% pepsin.

Animal based rennet typically contains 90% chymosin and 10% pepsin in purified form and is considered by many cheese makers to be the preferred rennet. Different ratios are available such as 92-85% chymosin and 8-15% pepsin.

Note, calf based rennet does not qualify for some diets and may concern some for animal welfare reasons.

Formats

Animal derived rennet is normally available in a liquid, paste, or powder formats with liquid easily being the most common.

Liquid format animal rennet contains, in addition to the enzymes chymosin and pepsin, trace proteins, sodium chloride brine, acetate, propylene glycol, caramel color, and flavour preservatives sodium benzoate, and potassium sorbate.

Powdered format animal rennet contains, in addition to the enzymes chymosin and pepsin, sodium benzoate and sodium chloride.

Manufactured liquid calf based rennet is often shipped in large i.e. 5 US gallon containers, and thus hobby Cheese Making Supply Stores often repackage into smaller containers.

Note, rennet paste is normally animal based and made of ground stomachs and brine. As it uses the whole stomach it is also rich in lipase which results in a piquant cheese such as Feta, Provolone, and Romano. Another choice to achieve this effect is to use liquid refined rennet and dried lipase powder.

Concentration

Liquid calf rennet is normally produced in a very concentrated form because when diluted, the enzymes become unstable and lose strength.

Liquid calf based rennet is normally available in single, double strength, and triple strength. To complicate matters, single strength in Europe is different from that in USA.

In the mid 1990’s a new standardization measurement (IDF Standard 157:1992) for rennet was adopted based on IMCU/mL or International Milk Clotting Units per ml of milk.

Fermentation

Malaka Brand Vegetarian Liquid Rennet Retail Box - CheeseForum.org
Malaka Brand Vegetarian Liquid Rennet Retail Box - CheeseForum.org

Until 1990, the only source of chymosin was calves. Around 1990, scientists created a system to make chymosin that doesn’t require calves. Using genetic engineering, the gene for chymosin was cut from a calf cell and inserted into the genomes of bacteria and yeasts such as Kluyveromyces lactis. The microbes replicate and grow rapidly, can be grown continuously, and make an exact copy of calf chymosin.

It can be argued that these rennets are not genetically engineered as nothing was changed in the gene.

This product is often certified Halal or Kosher and suitable for vegetarians.

Approximately 70% of the cheese made in the U.S. are coagulated using fermentation produced chymosin.

Formats

Fermentation produced rennet is normally available in concentrated liquid and powder formats.

Concentration

Fermentation produced rennet is 100% pure chymosin however it can be combined with pepsin to make a more natural animal based type product.

Microbial

Several forms of milk coagulating enzymes are based on microbial fungal sources, the most popular being Rhizomucor miehei, others being Cryphonectria parasitica or Endothea parasitica. Here the mold is grown in large vats and the enzyme extracted and purified and stored with salt.

While microbial rennets are effective at coagulating milk, they are not as good at making aged cheeses as their pathway after coagulation develops poorer flavor and texture than animal based rennet.

In general, microbial based rennets are cheaper than animal based rennets.

Formats

Microbial rennet is normally available in concentrated liquid, powder and tablet formats.

Tablet microbial rennet normally also contains microcristaline cellulose and sodium chloride (table salt).

Concentration

Liquid microbial based rennet is normally available in single or double strength.

Animal Based

CHR Hansen Brand 75 liter Packages Of Powdered Microbial Fermented Fungus
CHR Hansen Brand 75 liter Packages Of Powdered Microbial Fermented Fungus

Examples include thistle or fig leaf.

Formats

Concentrations

Wiki: Coagulation

Rennet coagulated good quality curd, checking with finger Clean break method.

All cheeses use coagulation of the milk as an essential cheese making step. This articles discusses how coagulation works and the different types generally used in cheese making.

General

After acidification, the next step in making cheese is coagulation. Coagulation of milk is the first step towards concentration of milk’s casein and fat and expulsion of whey made up of water and milk’s soluble components. During coagulation the casein micelles form long chains that branch in all directions and bond with themselves forming a three dimensional matrix that encompasses and all the milk including fat and water. Cheese makers call this matrix the curd.

The process of coagulation occurs through two different mechanisms, primarily acid coagulation and primarily enzyme coagulation. Each method results in two very different families of cheese. To be literally correct, rennet is the historical name of the product from animals, but in cheese making rennet is the generic term for all types of enzymes, whether of animal, plant, microbial or fermentation origin, that are used to coagulate milk.

The most common method is enzyme or rennet coagulation as it produces a lower moisture content and longer shelf life curd without excessive hardening. Virtually all hard cheese are made using rennet coagulation.

Lactic Acid Coagulation

General

Primarily lactic acid coagulated curd from store bought cow's milk after sitting overnight.
Primarily lactic acid coagulated curd from store bought cow's milk after sitting overnight.

Several soft cheeses such as cottage cheese, quark, and traditional cream cheese use lactic acid coagulation which occurs as response to a reduction in pH from production of lactic acid by the starter culture. Pasteurization including Ultra Pasteurization and UHT milks are fine for making Lactic Acid cheeses, they will give a thicker lactic acid set curd than when using raw milk.

The procedure for setting is to add a precise amount of mesophilic starter culture to milk at a temperature of ~21°C / 70°F, much lower than for rennet coagulated cheese, although some recipes – procedures use warmer temperatures.

The starter culture causes lactose to be converted to lactic acid, lowering the pH with full coagulation into a solid curd occurring around a pH of 4.6 – 4.7. This can take 4 to over 24 hours, depending on the temperature and the amount and activity level of the starter culture.

The curd that is formed from lactic acid coagulation is much weaker than from rennet coagulation and the curd more strongly resists the expulsion of whey. Thus the resulting cheese is softer and higher moisture than rennet coagulated cheeses.

As the resultant cheeses are softer and moister, they have a shorter shelf life and are consumed young and thus in some countries such as USA, milk is required to be pasteurized for health reasons.

Milk Type

Primarily lactic acid coagulated curd using store bought chocolate flavoured cow's milk.
Primarily lactic acid coagulated curd using store bought chocolate flavoured cow's milk.

For lactic acid coagulated cheeses, when cow’s milk is used, it is normally pasteurized or skimmed otherwise cream will separate during the long incubation time resulting in an non-homogeneous curd. Whole non-homogenized cow’s milk is used but the whole curd must be re-worked to form a homogeneous mixture. Some cheese making recipes-procedures use both acid and rennet coagulation, here rennet is normally added in significantly smaller amounts than when rennet coagulating milk as it is added not to cause coagulation but rather to enable better whey separation and better curd formation, and thus less cream separation when using non-homogenized milk.

Conversely non-homogenized sheep and goat’s milk do not easily cream and thus there is less need for rennet addition or homogenization in lactic acid coagulated cheeses, however some recipes still call for the addition of small amounts of rennet when using sheep or goat’s milk for lactic acid coagulated cheeses.

If using rennet in lactic acid coagulated cheeses, the lower setting temperature than for rennet coagulated cheeses still allows the non-enzymatic phase of rennet coagulation but not the second enzymatic phase.

Rennet Coagulation

General

Rennet coagulated good quality curd, checking with finger Clean break method.
Rennet coagulated good quality curd, checking with finger Clean break method.

Rennet coagulation originally used enzymes from the lining of the fourth stomach of calves and from the stomachs of kid or lamb as they have these enzymes naturally in their stomach to better digest milk and as that was what was commonly available. There are two prime enzymes in these stomachs that coagulate milk, initially chymosin and later after weaning, pepsin. It is the chymosin enzyme that is the stronger milk coagulant. Since the 1990’s other forms of “rennet” (fermentation, microbial) have been made.

Rennet coagulation is a two stage process involving an initial enzymatic phase during the first ~10 minutes where a chemical change is occurs as preparation for second non-enzymatic phase where the casein micelles start forming linked chains and eventually a full solid curd is formed, if enough calcium is present.

Rennet is discussed in detail in Wiki: Rennet, different types of rennet are discussed in Wiki: Rennet Types.

Milk Preparation

Milk is warmed to optimum rennet coagulation temperature of 30-36°C / 86-96°F. Higher temperatures up to ~40°C / 104°F result in faster coagulation times. Above 40°C / 104°F and the rennet becomes inactivated. Lower temperatures result in slower coagulation, below ~18°C / 65°F coagulation will not occur.

Starter culture, CaCl2, lipase, colourants such as Annatto and flavor additives must be added to the milk before renneting so that they are incorporated evenly in the curd. See Wiki: Ingredients, When To Add.

Other additives such as dill weed, caraway or cumin seeds, or smi dried fruit like apricots can be mixed in later, normally after the curd is cut and whey is drained.

Note, many rennet coagulated cheese making procedures have a pre-ripening time of up to 1 hour after adding the starter culture and before adding rennet.

Adding Rennet To Milk

Rennet coagulated store bought cow's milk curd, after diamond cutting, imprint of bowl from spinning bowl flocculation test.
Rennet coagulated store bought cow's milk curd, after diamond cutting, imprint of bowl from spinning bowl flocculation test.

Rennet is very concentrated, so adding it directly to the milk would cause it to set the milk in just that area and not in the overall milk. Even if one stirred it after adding directly, it would still coagulate in areas resulting in a poor curd formation. Therefore the common method of adding rennet is to first dilute / dissolve in cool non-chlorinated water before adding to the milk. Dilution amounts are discussed in the Animal Based Rennet webpage.

Best practices for rennet preparation and addition are:

  1. When ready to add rennet, dilute or dissolve rennet in cool un-chlorinated water. Chlorine is a strong oxidizing agent and rapidly destroys the rennet enzymes.
  2. Trickle the diluted rennet into the milk while stirring the milk with a skimmer for a maximum of 60 seconds in an up and down method without breaking to surface (no splashing). Do not dilute rennet in advance of adding to milk as its strength deteriorates when diluted.
  3. Stop the swirling of milk after stirring with skimmer to enable better coagulation.

Wiki: Body Defects, Moist

Body excessive moisture defects of cheese are common and can be associated with most cheese types. This article provides a description and some common causes and solutions organized by root cause.

Description

  • Texture of body of cheese is too moist and thus too soft.

Rennet

Causes

  • Too little rennet used and thus too much whey retained in the curds.

Solutions

  • For current batch, try to dehydrate by lowering storage environment humidity. Note, too quick dehydration can result in surface cracking.
  • For future batches, use appropriate amount of rennet.

Improper Cut Curds Stage

Causes

  • Curds cut into too large pieces or stirred too little or for too short a time or at too low a temperature resulting in excessive whey retained in the final curds.
  • Cut curds warmed too rapidly which initially cause rapid expulsion of whey from surface of cut curds but then results in the dehydrated layer inhibiting further expulsion of whey from interior of the cut curd piece.

Solutions

  • Cut curds into size, and/or stir more often and for longer time, and/or at temperature dictated by the cheese making recipe/method.
  • Warm cut curds slower at rate dictated by the cheese making recipe/method.

pH Too High

Causes

  • Acidity level in cheese is not high enough

Solutions

  • For current batch, ripen longer.
  • For future makes, use more starter.

Poor Pressing

Causes

  • For pressed cheeses, inadequate pressing (pressure and/or time and/or temperature) resulting in excess moisture held in body of cheese. Note that the intent of pressing is to remove voids between the cut curds, ensure a good knit of the cut curds and to form a dehydrated layer of curds at the cheeses surface to act as a tough rind, it is not to expel excess whey, that is done in the curd forming stage.
  • Some formed cheeses are not pressed when made commercially or by artisans, however if large, they are actually pressed using their own weight. For example commercial Stilton cylinders are typically 8 kg / 17 lbs and are formed by turning the cut curds in large hoops where the cheeses own weight acts to lightly press the cheese. Scaled down such cheeses to smaller makes requires light pressing to arrive at the optimal moisture content.

Solutions

  • For current batch, try to dehydrate by lowering storage environment humidity. Note, too quick dehydration can result in surface cracking.
  • For future pressed cheese makes, use amount of pressure and/or time and/or temperature determined in cheese making recipe/method.
  • For future normally pressed by own weight type cheeses, apply light pressing dependant on batch size.

Poor Aging Environment

Causes

  • If formed cheese, aging environment’s humidity is too high resulting in excessive moisture retention in cheese.

Solutions

  • If formed cheese, reduce aging environment’s humidity to enable more dehydration of cheese.