User:Bertille Jacquart/sandbox1

I decided to change my topic for the assignment and chose to talk about Goat cheese. The current wikipedia page about Goat Cheese is almost empty, it contains a small paragraph about the cheese's properties and another one listing goat's milk cheeses by region.

I'm going to create a leading section for this page and try to complete informations about the properties by adding description of the production and the chemical composition.

Introduction

“Chèvre” or goat cheese is a food term used to designate cheese made out of goat milk. Goat domestication for milk production started approximatively 10 000 years before Jesus Christ. It represents a real part of the Mediterranean culture, as you can notice its presence in many writings such as Homer’s Odyssey. Goat cheese consumption was initiated by the Gallo-romans who used to eat it macerated in olive oil. Further on, goat breeding spread out in France, mostly in the South. Around 1880 farmers stated to gather and form cooperatives, concentrating around Centre, Poitou-Charentes and Rhône-Alpes regions. By this time, Loire River Valley became a huge site of production and retains today about 70% of the total goat cheese production and France appears at the top of the podium in term of production per country with approximatively 110,000 tones per year. Nowadays goat cheese production has highly evolved and every steps of the process are regulated and controlled carefully. You can find over hundreds of kinds of goat cheese differing in shape or flavors, the most famous French ones being Bucheron, Chabis or even Crottin de Chavignol. Its unique flavor and aroma rely upon its moisture, density, aging and flavoring processes that will be develop along this expose. In a first place it is important to describe the goat milk composition in order to understand how the cheese is then made.

Chemical composition

Goat milk differs from cow milk in a way of being lower in fat. Fat contents represents 4% of the total composition of cow milk when only 3,44% for goat milk.

a. Proteins

Casein

Goat milk contains 30,8g/ kg of proteins. It is important to quantify it because it represents the casein concentration. Casein is a conjugated protein, it will form micelles by binding with phosphate groups. Those groups will then bind calcium, which is important for micelles structures. The micelles will later form aggregates that is essential to cheese production. Proteins have a preponderant role and are essential to cheese making process. Casein can represent up to 70% of the total amount of proteins in goat milk. But all caseins in milk cannot form micelles as a part of it is lost in the aqueous phase.

Casein can be found in milk under four different types: - α(s1) – Casein: low concentration in goat milk making it more digestible than cow milk. - α(s2) – Casein: major casein proteins with (s1) – Casein. - β - Casein: more hydrophobic than caseins and very sensitive to calcium concentration. - κ - Casein: it is found on the surface of the casein micelles (hairy layer) and is a huge factor concerning the cheese making process. Casein micelles structures will lead to aggregation due to several type of interactions: - Van der Waals interactions will cause aggregation under all circumstances. - Electrostatic interactions will create a repulsive force that will vary with pH. - Steric interactions will also create a repulsion force due to - Casein on the surface of the micelle. Casein is important to the functional behavior of dairy products.

Whey protein or serum protein

Whey proteins are the one that will remain after the coagulation of casein micelles. Those proteins will not coagulate but form a liquid during the process of cheese making. They are non-desirables products in cheese. However, they represent 20% of protein in goat milk. Whey contains the most part of lactose.

b. Fat contents

Goat milk contains less fat than cow milk. The goal here is not to obtain the largest amount of fat possible as we do for proteins. But just to control the amount because fat can impact the cheese making process: a too low concentration can be a reason the cheese won’t meet regulations expectations when a too high concentration can limit the process and create a non-usable unit. Fat content in milk is represented by fat globules. Phospholipids forming a tri-layer and associated substances such as cholesterol will create the membrane that retain the triglycerides present in the middle of the fat globule. Triglycerides are fatty acids (saturated and unsaturated) that represent 98% of the total of fat contents.

c. Lactose

Lactose is a specific sugar present in the milk. It is synthetized in the mammal and found in equal quantities in cow and goat milk. Its main role is to be a substrate for the lactic bacteria during the cheese making process. Those bacteria dispose of an enzyme, -galactosidase, which is responsible for the cleavage of lactose molecules in two different and distinct molecules: glucose and galactose. Those sugars will then be used during the formation of lactic acid, responsible for the drop of pH during the cheese making process.

d. Minerals

Goat milk is composed of several minerals such as sodium, potassium, magnesium and calcium. Those are ions that are positively charged. But goat milk is also composed of negatively charged ions such as chloride, sulfates, phosphates. Phosphate and calcium will directly influence the cheese fabrication. They can be found under two different phases, aqueous and micellar (bounded to casein micelles) at equilibrium. The equilibrium can be perturbed by a change in physical and chemical properties. Their concentration will define milk capacity to resist to acidification.

e. Microbial agents in cheese fabrication

Goat milk and milk in general contains three different types of micro-organisms. - Bacteria: some are useful or even necessary for the cheese making process (thermophile and lactic thermophiles) when others are detrimental or even dangerous for the making of a good and regulated cheese. - Moulds: those that develop in acid environments will act during the aging process (penicilium candidum). - Yeasts: transform sugars in alcohol and will also be a factor of aging (candida).

Structure

Milk in a general way is divided in three different phases: - The aqueous phase contains the lactose, soluble minerals components, steric proteins, non-protein nitrogen and the soluble fraction of casein. - The micellar or colloidal phase contains the major part of casein and the insoluble part of mineral components. - The third and last phase contains elements in suspension such as fat globules, leucocytes and microbial cells. As you can see on this picture, fat globules present in milk are dispersed in the liquid/ aqueous phase mostly composed of water. Plasma defines this watery part of the milk. When the serum is basically all that is not fat globules or casein. Casein present in the dispersed phase will form colloidal complex called micelles. The hairy layer, highly concentrated in calcium ions creates a protective layer on the surface of casein micelles.

Manufacture

Cheese making is a process in which water, lactose and some minerals while be removed from the milk to create a concentrate of milk fat and protein. Cheese is a food product made from mammal’s milk, mostly cows and goats. It comes in many different and specific varieties. Each variety is defined by ingredients that will be used in the process, the type of processing and the characteristics the cheese will get through it. In order to make cheese, you will always start the process with raw milk. Cheese can be made using this raw milk or a pasteurized milk. Milk is the main ingredient in cheese, with enzyme, bacteria and salt. Cheese making follows a particular process. Every step gives place to physical and chemical reactions responsible for the making of the cheese as it will be described below.

a. Pasteurization / Heat treatment of milk Depending on the cheese you want to make, pasteurization can be the first step of the process. The goal here is to heat the milk in order to destroy pathogens (harmful bacteria, micro-organisms). This step is simple, you just have to heat the milk to a temperature of 63° Celsius for about 30 minutes. For hard cheeses, raw milk is warmed at the optimum temperature (about 32° Celsius) to promote cheese culture development and destroy some of the spoilage organisms. The main objective of this step is to first decide what type of cheese you want to make and adapt your practice in order.

b. Cooling

The milk is then cooled to get it at the right temperature starter bacteria need to grow. Once the milk reached the right temperature, starter and non-starter bacteria are added to the milk. The temperature is maintained at 32° for 30 minutes to allow ripening and make bacteria begin fermentation by lowering the pH and starting to develop cheese flavor.

c. Culturing

Culturing is the step where you add both starter and rennet to the milk. Starter bacteria are added to milk because it helps to initiate the cheese making process. They convert lactose into lactic acid to help lower the pH of the milk. There are two different types of bacteria used: - Mesophilic bacteria thrive at room temperature but die at higher temperatures. They are used to make mellow cheeses, such as Cheddar, Gouda and Colby. - Thermophilic bacteria thrive at higher temperatures, around 55 °C, and are used to make sharper cheeses such as Gruyère, Parmesan and Romano. Rennet is an enzyme secreted in the stomach of calves. Added to milk, it will act on milk protein especially on -Casein. It will lead to milk flocculation and more precisely micelle aggregation. Rennet will speed up the process, it also allows it when the acidity is lower than usual (in case of certain type of cheese making). The duration of this process depends on the temperature and the acidity you decide to apply. Optimum temperature can be between 18 and 25° Celsius. Acidity will increase, meaning it will lower the pH and affect the structure of casein micelles. This acidification is responsible for the increase of the aqueous solubility of the Calcium and Phosphate of casein micelles and will engender the destabilization of the micelles. Furthermore, the acidification as to say the change in pH will affect the electrostatic repulsion. In different words, rennet will cut-off the hairy layer of casein micelles. Those micelles will progressively lose their negative charges on their surface and will no longer be stable in solution. They will aggregate.

d. Cut curd and heat

The aggregation will get the micelles to stick together and form a fractal network. It will form a semi-solid structure called curd. The curd will form a firm coagulum. Until it reaches a pH of 6,4, the curd is left to fermentation. The curd will then be cut in small pieces, squares most of the time, using special knives (cheese vat’s knives). All the different pieces of “cheese” will be heated up to 38° Celsius to separate the whey from the curd.

e. Draining Whey and Texture curd

By draining the whey, the goal is to obtain liquid phase which is whey and a solid phase which is curds. The whey is then drained away. This process is supported by vat: whey is drained from it and the curds form a mat. The earlier acidification of the milk clearly helps to separate the curds. The whey collected from cheese making process was for a long time considered as waste but its use to control environmental impact and issues is currently increasing in the food industry due to interesting functional properties (emulsification, flavor enhancement, solubility…). Additional processing can help release more whey. Curd mats are cut into sections and piled on top of each other. You want to flip the pile periodically to help expel more whey. Fermentation continues until curds reach a pH of 5,1 up to 5,5. Then you want to cut the curd mats into smaller pieces because mats might have formed a thigh matted structure.

f. Salting and molding

Salting is the action of adding salt to the curd. This might seem like an easy step yet really important. It allows: additional draining, flavor formation, formation of a thin and hard surface, microbial selection. Curd pieces are put back in the vat and dry salt is added to be mixed to the curd. The salted curd pieces are then put in cheese hoops to be pressed into cheese blocks. Those blocks are place on stainless steel or plastic grids and the molding activity will start. To do so, the cheese blocks are exposed in a dry room ventilated by dry air and equipped of air extractors. A period of warm air ventilation will be followed by a period of cold air ventilation. This step will last between two to three days.

g. Storing and Aging

The next step consists of putting the cheese in coolers with a temperature between 8 and 12° Celsius, and leave it there until the desired age is reached. Humidity and acidity will decrease, the cheese will get most of its flavor through the transformation of fat contents into fat acids and the molding. Cheese depending on what type can age from several months to several years.

h. Packaging

Once the cheese reached the maturity wanted, the blocks can be packaged or waxed. This can be done in manufacturing facilities or if produced in farms directly by farmers. The packaging will have to follow the leads and regulations of the FDA to be sold as a food product.

i. Shelf life

Depending on what kind of cheese you made, its moisture content will change. The highest the moisture content is the less you will be able to keep the cheese. This is due to the fact that micro-organisms responsible for the alteration of the food develop more quickly in a humid environment. Moulds developing on the surface of the cheese and forming white trace are undesirable and are a sign that the cheese is starting to be to old.

Physical properties

a. Colloidal interactions

Milk is considered being a colloid, in fact milk is an emulsified colloid. Fat globules are dispersed in a water based solution. There are three types of colloidal interaction that are characteristic to milk and the cheese making process. - Van der Waals: is an attractive interaction between particles in solution. Those interactions are the reason the colloid will be stable. - Electrostatic: reflect the repulsive action of charges on surfaces of particles in solution. - Steric: reflects the complex interactions between particles in solution. Those particles randomly floating, as they get closer will start to interact creating an increase in the entropy. Energy will increase as particles repeal one another and get apart. Those interactions are sensitive to a change in physical and chemical properties. As it happens during the cheese making process. A drop in pH will highly affect electrostatic interactions. Calcium ions present on the casein micelles surface will lose their negative charges. Casein micelles will stop repeal each other and start to aggregate. Van der Waals interactions will no longer be able keep the solution stable and steric interactions will be diminished as molecules start to stick to one another.

b. Viscosity Viscosity of milk can help determine the flow conditions for dairy processes. Milk and skim milk appear to have a Newtonian behavior. Milk is a thin fluid whose viscosity is independent of the shear rate. The viscosity of milk depends on the following: - Temperature: a lower temperature will increase the viscosity as it will increase the volume of casein micelles. When a temperature above 65° will increase the viscosity due to the denaturation of whey proteins. - pH: a change in the pH will affect the colloidal properties and increase the viscosity. As the milk is transform during food processes, it will become more shear rate dependent (shear thinning).

Types of cheese

a. Fresh or unripen

Fresh goat cheese is the type of cheese that American people will often associate to “chèvre”, the French word to say goat. It is probably the most famous type of goat cheese. Its aspect is soft and its texture can vary from a cream-cheese type of consistency to a thicker and more spreadable. In this case, the cheese will be dry and have crumbly edges. Fresh goat cheese will often be shaped in a round form, looking like a high hockey puck. But you can also find dome or even pyramids shapes. This type of cheese has the highest moisture content, they are not aged and need to be consumed quickly. Soft cheeses can be made only by draining and not pressing. Examples: spreadable goat cheese, fresh log, goat feta, le Cornilly…

b. Soft-ripened with natural rinds

For this type of cheese, the air will dry the outside of the cheese naturally during the aging process. It will lead to the formation of a thin crust overtime called the rind. It is obtained without pressing the cheese. Examples: Bûcheron, Chevrot, Crottin, Chabichou du Poitou…

c. Soft-ripened with a flavored crust

To form soft-ripened chees, you can also coat the outside of the cheese with a mixture of Penicilium candidum during the making process. The rind that will form is white and can sometimes be bloomy. This technique is called mixed curdling. Examples: goat Camembert, goat Brie, Brique de Chèvre…

d. Soft-ripened with washed crusts

Cheeses of this family have a lower humidity rate than the previous ones. It means that they are less alterable and will be able to be kept for a longer time without consuming. They can be aged for about 6 months. During this step cheeses are washed with salt water or a simple brush to accelerate the formation of the crust. To obtain a good washed crust cheese, it has to age for at least 2 to 3 months. Examples: Maroilles, Pont l’Evêque…

e. Aged or hard goat cheese

It has the lower moisture content of them all, it is aged until it reaches a certain texture. The texture wanted is firm or even hard. The flavor will largely differ from fresh cheese due to the aging process, it will release aromas and flavors contained in the milk. It is less tangy and will develop nuttier or sharper flavor notes. If the cheese is aged for a long time, it will start develop blue mold. This process is stopped by the action of wrapping the cheese in a clean sheet. Examples: Tomme de chèvre, Bleu de chèvre…

Conclusion

Concerning the goat milk industry, goat cheese retains the most valuable part among all the goat milk products. Due to its lower fat content and more digestible properties, goat milk offers a unique range of cheese product. The USDA reported that today, it exists over 400 different varieties of goat cheese or cow and goat milk combined cheese. Cheese making process is complex but requires a good understanding of milk and cheese physical and chemical properties. The casein micelles structure is such that the action of adding starter and rennet will completely change the structure of the raw product, milk. The acidification due to the transformation of lactic bacteria into lactic acid micelle aggregation and a complete change in the network arrangement. The rest of the process will define the characteristics of the cheese you want to make.

Bibliography

Books Foard Maggie. Goat Cheese. Gibbs Smith. 2009.

Park Young W., Haenlein George F. W., Handbook of Milk of Non-Bovine Mammals. John Wiley & Sons, 2008. 472p.

Pond Wilson G., 2004. Encyclopedia of Animal Science. 952p. CRC Press.

Pradal Magali. La transformation fromagère caprine fermière. Lavoisier, 2012. 295p.

Articles Horne David S., Casein micelle structure: models and muddles. Volume 11, Issues 2–3, June 2006, Pages 148–153 Park Yong W., Goat Milk Products: Quality, Composition, Processing, and Marketing. Agriculture research station. Phadungath Chanokphat. Casein micelle structure : a concise review. Songklanakarin J. Sci. Technol., 2005, 27(1) : 201-212 Raynal Ljutovac K., Composition of goat and sheep milk products. Volume 79, Issue 1, September 2008, Pages 57–72 Zeller Bruno. Le fromage de chèvre : spécificités technologiques et economiques. Ecole vétérinaire de Toulouse. 2005

Websites Style highlight: fresh goat cheese: http://culturecheesemag.com/cheese-iq/style-highlight-fresh-goat-cheese-chevre

Chèvre: http://www.cheese.com/chevre/

Milk Facts – Cheese production: http://milkfacts.info/Milk%20Processing/Cheese%20Production.htm#Adjunct

Cheese making technology ebook : https://www.uoguelph.ca/foodscience/print/book/export/html/335

Biotechnology learning – The science of cheese: http://biotechlearn.org.nz/focus_stories/cheesemaking/the_science_of_cheese

Biotechnology learning – Use of whey http://biotechlearn.org.nz/focus_stories/cheesemaking/uses_of_whey

Families of cheese: http://www.lebeurrebordier.com/en/collection/fromages/les-familles-de-fromages/

Varieties and textures of French chèvre: http://goatcheesesoffrance.com/the-cheeses/

All about goat cheese: https://www.craftsy.com/blog/2013/09/all-about-goat-cheese/