1. Introduction

2. Mechanical processes
    Creaming butter and sugar  Butter  Sugar & leavening agents  Eggs  Flour  Salt 

3. Chemical processes
    Release of trapped water  Protein denature  Water vapour  Maillard reaction  Caramalization 

4. References

Introduction

Baking is as much science as it is art and there are many chemical forces involved. The effect one ingredient can have when baking is not often pondered. Many basic cookie recipes, for example, chocolate chip cookies, have similar ingredients; butter, sugar, eggs, and baking soda/[https://en.wikipedia.org/wiki/Baking_powder/ powder], flour, salt and chocolate chips. Each one of these ingredients, depending on the quantity added, their composition when added and the ingredients added with them, can significantly change the outcome of a cookie.

Mechanical processes

Creaming butter and sugar

[https://en.wikipedia.org/wiki/Creaming_(food)/ Creaming] is a different process than stirring, mixing or beating. It isn’t about combining ingredients, it’s about aerating them. Creaming the butter and sugar together is a necessary step to make the cookies fluffier, but it also creates more dough and can give additional cookies depending on the recipe. Sugar crystals have sharp edges, and these edges can cut into the first fat phase creating small pockets of air; a process known as aeration. ^[1] These small pockets allow for air to enter and create a network of sugar crystals, fat and air. Sugar is the base for which fats and starch granules are embedded and if sugars do not dissolve, these matrices cannot be formed. Sugars cannot readily dissolve within fats either, but when subjected to a creaming process they can dissolve. Half the sugar is dissolved during this process and the other half is dissolved once in the oven. Air is a poor conductor of heat, meaning that these air pockets help to insulate the dough when baking in the oven ^[2]. This slows the rate at which the butter and sugar melt as the air pockets fill with steam and swell the cookie.

Butter

The temperature of the fat used, along with the type of fat used, has significant effects on the aeration process. Butter is about 20% water and at room temperature it exhibits a plastic behavior ^[3] As the temperature is lowered, butter becomes less spreadable due to formation of [https://en.wikipedia.org/wiki/Triglyceride/ triacylglycerol] crystals.^[4] If the butter is too cold, then the two cannot mix and air bubbles will not form. If the butter is too warm, then the air bubbles created will collapse, leaving you with a dough that lacks air bubbles. The air bubbles aid in creating a cookie that is light and fluffy, therefore, if there’s no air bubbles, or they don’t stay, the final cookie will be denser than if the butter was at room temperature. Butter begins to melt around 90°F, however, it loses its ability to stretch and expand after 68°F; careful consideration should be made into the butters' temperature or the final result might be collapsed cookies. ^[5] Some sources say to use butter at 65°F, but this does not consider that the doughs' temperature will increase slightly when adding room temperature ingredients or from friction when mixing.

Sugar & leavening agents

Sugar is not solely used for sweetness, it is also a vital part of the cookie structure, as it is a tenderizer and browning agent. It is also [https://en.wikipedia.org/wiki/Hygroscopy/ hygroscopic], meaning that it readily takes up water in order to undergo reactions. Brown sugar is a denser sugar and can compact easier; this means that the cookies will contain few air pockets and therefore rise less but spread more compared to recipes that use white sugar. However, there will be less moisture escaping via steam and therefore the cookies tend to stay more moist and chewy than cookies with white sugar. Brown sugar also happens to be acidic and therefore can readily react with sodium bicarbonate (baking soda); making the cookies thick, puffy and soft due to the carbon dioxide that is produced. Whereas, [https://en.wikipedia.org/wiki/White_sugar/ white sugar] is neutral in [https://en.wikipedia.org/wiki/PH/ pH] and cannot participate in this reaction which leads to a thinner, denser and crisper cookie compared to when brown sugar is added.

[https://en.wikipedia.org/wiki/Baking_powder/ Baking powder] is [https://en.wikipedia.org/wiki/Sodium_bicarbonate/ baking soda] but with the acid already in it; therefore, when subjected to water, baking powder will undergo the same reaction as baking soda and brown sugar mixture. Carbon Dioxide is released and enlarges the air pockets that were already present from creaming together the butter and sugar.^[6] If the desired result is to have a soft and puffy cookie, then white sugar could be used with baking powder (provided there are a few other alterations to the recipe) or brown sugar could be used with baking soda. Note: If a recipe calls for a mixture of both sugars, then play around with the amounts to achieve personal desired results but if the recipe calls for all of one sugar and none of the other, it is most likely to obtain a specific result. Additionally, different recipes contain different ingredients and can cause the sugar to react in a number of ways. For example, one recipe can be made with melted butter and baking soda, and one with creamed butter and baking powder. It's possible that these two recipes will create a similar type of cookie because it is possible that the sugar chosen will fail in some aspects but excel in others. Brown sugar doesn’t aerate as well as white sugar because of its density and thus produces cookies that don’t rise as much. However, unlike the white sugar, it does react with the baking soda which causes leavening. Therefore, the sugar should be chosen wisely. If the final product is too dense, the culprit is likely the leavening agent.

Eggs

Flour

Salt

Chemical processes

Release of trapped water

At 92°F, the butter melts and this allows for trapped water within the emulsion to be released. Butter is an emulsion of water in fat and is held together with dairy solids. An emulsion is a mix of two liquids which are mutually insoluble and to separate them, the interfacial film must be destroyed and the droplets made to coalesce. This process occurs during an increase in temperature because of the reduction in viscosity of the oil which increases the settling rate of water droplets and their collision rates. ^[10] This weakens/ruptures the film due to water expansion and it also increases the difference in densities causing the cookie to flatten out, but thankfully it will not flatten out forever and this is thanks to the proteins within the eggs.

Protein denature

At 144°F proteins begin to [https://en.wikipedia.org/wiki/Denaturation_(biochemistry)/ denature]. As know, an increase in temperature increases the available energy and therefore increases the amount of bonds breaking. Heat disrupts the normal alpha helix and beta sheets, causing proteins to uncoil into a random shape. The first structure that is affected is the overall shape of the protein, the [https://en.wikipedia.org/wiki/Protein_structure#Tertiary_structure/ 3° structure]. Both this structure and the [https://en.wikipedia.org/wiki/Protein_structure#Secondary_structure/ 2° structure] are held together by H-bonds, Van der Waals forces and sulfur bonds.^[11] The 2° structure is then affected and the proteins will uncoil until you are left with the 1° structure; the specific sequence of amino acids. This sequence contains both [https://en.wikipedia.org/wiki/Hydrophile/ hydrophilic] and [https://en.wikipedia.org/wiki/Hydrophobe/ hydrophobic] sections; the hydrophilic sections attract water molecules and the hydrophobic sections attract hydrophobic sections of other uncoiled proteins. This creates a lattice-work structure that grows amorphously and has water molecules entrapped within. ^[12] This is what gives substance to the once runny dough.

Water vapour

At 212°F, water begins to boil away and creates vapour. This vapour pushes up on the cookie and tries to escape, which is what creates airy pockets and dries the cookie out. Helping with this process is the baking soda, as mentioned earlier. Baking soda has a low bench tolerance, which means that it levels quickly. Baking soda requires water in order to react BUT most of the water is tied up in the butter and cannot react until it melts; part of the water reacts with the sodium bicarbonate and creates carbon dioxide and part of it evaporates out. When heated and subjected to water, the alkali and the acid react and neutralize the acidic ingredients like brown sugar and produce carbon dioxide, thus aerating out the dough.

Maillard reaction

At 310°F, the [https://en.wikipedia.org/wiki/Maillard_reaction/ Maillard Reaction] begin. This is a reaction that gives browned food its flavour and aroma. It is a [https://en.wikipedia.org/wiki/Food_browning#Non-enzymatic_browning/ non-enzymatic browning process] and occurs when proteins and sugars break down and rearrange themselves into a ringed structure. These new ringed structures actually reflect light and are what gives foods such as turkeys and hamburgers their browned colour.^[13] It can also produce a wide range of flavour and aroma compounds that are even able to react with one another and create even more complex flavours and smells.^[14] It all begins when the reactive carbonyl group of the sugar reacts with the nucleophilic amino group of the amino acid and produce an N-substituted unstable glycosylamine. The glycosylamine then [https://en.wikipedia.org/wiki/Isomerization/ isomerizes] by an Amadori rearrangement allowing it to form [https://en.wikipedia.org/wiki/Ketosamine/ ketosamines]. Note: the Amadori rearrangement is an organic reaction that describes an acid or base catalyze isomerization of the reaction of n-glycoside of an aldose ot glycosylamine to the corresponding 1-amino-1deoxy-ketose and is a carbohydrate chemistry.

These [https://en.wikipedia.org/wiki/Ketosamine/ ketosamines] then have multiple ways of reacting. Option 1, it produces two water molecules and reductones. Option 2, short-chain hydraulic fission products like diacetyl, aspirin, and [https://en.wikipedia.org/wiki/Methylglyoxal/ pyruvaldehyde]. Option 3, it produces brown nitrogenous polymers and [https://en.wiktionary.org/wiki/melanoidin#English/ melanoidins]. These can then further react through dehydration and de-amination to produce [https://en.wiktionary.org/wiki/dicarbonyl#English/ dicarbonyls] which react with the amine to produce Strecker aldehyde. The outcome of this whole process is dependent on the type of amino acids present in the food.

Caramalization

Caramelization occurs at different temperatures for different sugars but generally happens around 350°F. It occurs when sugar molecules break down under high heat; they change from odourless crystals into a brown, fragrant liquid. This forms compounds that are sweet, nutty and slightly bitter; known as caramel compounds. The main difference between caramelization and Maillard is that it is a pyrolysis not a reaction with amino acids; meaning it only requires heat in order to undergo reaction. The first step is the decomposition of sugar. Sucrose, a disaccharide breaks down into its constituent monomers fructose and glucose as a common example found within cookies. The second step is the decomposition of the two monomers that were formed and this creates the [https://en.wikipedia.org/wiki/Aroma_compound/ aroma molecules] such as ester, furans and maltol. Instead of decomposition, the monomers can also undergo a condensation oligomerization meaning that the monomers continuously react with one another and create continuously larger molecules. Depending on the size and the concentration of carbon, you will get Caramelan, Caramelen and with further heating Caramelin.

The Maillard reaction and caramelization are both non-enzymatic browning processes that have distinctive and characteristic smells. Once you can smell them, it is an indication that the cookies are done and it can work just as well as a timer itself!

References

• Saint Paul's Church, Dover
• Saint Paul's Church, Mullingar
• Saint Pauls College
• Saint Paul's Ecclesiological Society
• Saint Paul Seminary (Minnesota)
• Saint Paul Seminary (Saint Paul)
• Saint Paul Seminary School of Divinity
• Saint Paul's Hospital of Tacloban
• Saint Paul's Hospital (Tacloban)
• Saint Paul Sisters of Chartres
• Saint Paul's monastery
• Saint Paul's Orthodox Church
• Saint Paul's sandwich
• Saint Paul's Tigers men's basketball
• Saint Paul Tsaramasoandro Philosophate
• Saint Paul (Velázquez)
• Saint Pelagia
• Saint Perfectus
• Saint Pergat
• Saint Pete Pier
• Saint Peter and Paul Cathedral
• Saint Peter and Paul Cathedral, Karlovy Vary
• Saint Peter and Saint Paul Church, Wolverhampton
• Saint Peter and Saint Paul (El Greco)
• Saint Peter and Saint Paul (El Greco, St Petersburg)