Editing Croissant (section)

==Ingredient functionality during processing==

===Predough===
[[Gluten]] proteins affect the water absorption and [[Viscoelasticity|viscoelastic]] properties of the predough.<ref name=":0">{{Cite journal|last1=Ooms|first1=Nand|last2=Pareyt|first2=Bram|last3=Brijs|first3=Kristof|last4=Delcour|first4=Jan A.|date=2016-10-02|title=Ingredient Functionality in Multilayered Dough-margarine Systems and the Resultant Pastry Products: A Review|journal=Critical Reviews in Food Science and Nutrition|volume=56|issue=13|pages=2101–2114|doi=10.1080/10408398.2014.928259|issn=1040-8398|pmid=26177127|s2cid=566664}}</ref> The role of proteins can be divided into two stages of dough formation: hydration and deformation. In the hydration stage, gluten proteins absorb water up to two times their own weight. In the deformation or kneading stage, the action of mixing causes the gluten to undergo a series of polymerization and depolymerization reactions, forming a viscoelastic network. Hydrated [[glutenin]] proteins in particular help form a polymeric protein network that makes the dough more cohesive. On the other hand, hydrated [[gliadin]] proteins do not directly form the network, but do act as plasticizers of the glutenin network, thus imparting fluidity to the dough’s viscosity.<ref>{{Cite journal|last=Wieser|first=Herbert|date=2007-04-01|title=Chemistry of gluten proteins|journal=Food Microbiology|volume=24|issue=2|pages=115–119|doi=10.1016/j.fm.2006.07.004|issn=0740-0020|pmid=17008153}}</ref>

[[Starch]] also affects the viscosity of predough. At room temperature and in a sufficient amount of water, intact starch granules can absorb water up to 50% of their own dry weight, causing them to swell to a limited extent.<ref name=":3">{{Cite journal|last1=Goesaert|first1=H.|last2=Brijs|first2=K.|last3=Veraverbeke|first3=W. S.|last4=Courtin|first4=C. M.|last5=Gebruers|first5=K.|last6=Delcour|first6=J. A.|date=2005-01-01|title=Wheat flour constituents: how they impact bread quality, and how to impact their functionality|journal=Trends in Food Science & Technology|series=Second International Symposium on Sourdough: From Fundamentals to Applications|volume=16|issue=1–3|pages=12–30|doi=10.1016/j.tifs.2004.02.011}}</ref> The slightly swollen granules are found in the spaces between the [[gluten]] network, thus contributing to the consistency of the dough. The granules may not be intact, as the process of [[Milling (machining)|milling]] wheat into flour damages some of the starch granules. Given that damaged starch granules have the capacity to absorb around three times as much water as undamaged starch, the use of flour with higher levels of damaged starch requires the addition of more water to achieve optimal dough development and consistency.<ref name=":0" />

Water content affects the mechanical behavior of predough.<ref name=":0" /> As previously discussed, water is absorbed by gluten and starch granules to increase the [[viscosity]] of the dough. The temperature of the water is also important as it determines the temperature of the predough. In order to facilitate processing, cold water should be used for two main reasons. First, chilled water provides a desirable environment for gluten development, as the temperature at which mixing occurs impacts the dough’s hydration time, consistency, and required amount of mixing energy.<ref>{{Cite journal|last1=Huang|first1=Weining|last2=Kim|first2=Yangsoo|last3=Li|first3=Xianyu|last4=Rayas-Duarte|first4=Patricia|date=2008-11-01|title=Rheofermentometer parameters and bread specific volume of frozen sweet dough influenced by ingredients and dough mixing temperature|journal=Journal of Cereal Science|volume=48|issue=3|pages=639–646|doi=10.1016/j.jcs.2008.02.008}}</ref> Secondly, cold water is comparable to the temperature of the roll-in fat to be added later, which better facilitates the latter’s incorporation.<ref name=":0" />

In-dough fat affects the texture and lift of predough. Although higher levels of dough fat may lower dough lift during baking, it also correlates with a softer end product.<ref name=":0" /> As such, the main function of in-dough fat is to produce a desirable softness in the final croissant.

===Lamination===
In [[Laminated dough|laminated]] croissant dough, the gluten network is not continuous. Instead, the gluten proteins are separated as thin gluten films between dough layers. The formation of thin, well-defined layers affects the height of dough lift. Generally, laminated croissant dough contains fewer layers than other puff pastry doughs that do not contain yeast, due to the presence of small bubbles in the gluten sheets. Upon proofing, these bubbles expand and destroy the integrity of the dough layers.<ref name=":5">{{Cite book|title=Technology of Breadmaking|last=Bent|first=Alan J.|date=2007-01-01|publisher=Springer US|isbn=9780387385631|pages=245–274|doi=10.1007/0-387-38565-7_9 |chapter=Speciality Fermented Goods}}</ref> The resulting interconnections between different dough layers would over-increase [[dough strength]] and allow water vapor to escape through micropores during baking, consequently decreasing dough lift. The role of fat also influences the separation of layers, as will be discussed next.

Roll-in fat affects the flakiness and flavor of the croissant. In [[laminated dough]], fat layers alternate with dough layers. As such, the most important function of roll-in fat is to form and maintain a barrier between the different dough layers during sheeting and folding.<ref name=":0" /> As previously stated, the ability for fat to maintain separation between folded dough layers ensures proper dough lift.

The type of roll-in fat used is typically [[butter]] or [[margarine]]. Butter and margarine are both water-in-oil [[emulsion]]s, composed of stabilized water droplets dispersed in oil.<ref>{{Cite journal |last=McClements |first=David Julian|date=2010-03-04|title=Emulsion Design to Improve the Delivery of Functional Lipophilic Components|journal=Annual Review of Food Science and Technology|volume=1|issue=1 |pages=241–269 |doi=10.1146/annurev.food.080708.100722|pmid=22129337|issn=1941-1413}}</ref> While butter is appealing due to its high consumer acceptance, its low melting point, {{convert|32|°C|°F|abbr=on}}, actually makes it undesirable for production purposes. The use of butter as roll-in fat during the lamination step will cause problems of oiling out during sheeting and fermentation if the temperature is not tightly controlled, thus disrupting the integrity of the layers.<ref name=":0" /> On the other hand, kinds of margarine are commonly used as roll-in fat because they facilitate dough handling. Generally, roll-in margarine should have a melting point between {{convert|40|and|44|C|F}}, at least {{convert|3|°C|°F|abbr=on}} higher than the fermentation temperature to prevent oiling out prior to baking. It is also important to consider the plasticity and firmness of the roll-in fat, which is largely determined by its solid fat content. Generally, a greater proportion of solid fat coincides with larger croissant lift.<ref name=":1">{{Cite book|title=Baked Products|url=https://archive.org/details/bakedproductssci00cauv|url-access=limited|date=2006 |publisher=Blackwell Publishing |isbn=9780470995907 |editor-last=Cauvain|editor-first=Stanley P.|pages=[https://archive.org/details/bakedproductssci00cauv/page/n85 72]–98|doi=10.1002/9780470995907|editor-last2=Young|editor-first2=Linda S.|chapter = Ingredients and Their Influences}}</ref> At the same time, the roll-in fat should have plasticity comparable to that of the dough, such that the fat layers do not break during sheeting and folding.<ref name=":0" /> If the fat is firmer than the dough, then the dough can rupture. If the fat is softer than the dough, then it will succumb to the mechanical stress of sheeting and potentially migrate into the dough.

===Fermentation===
[[File:Croissant, cross section.jpg|thumb|Cross-section, showing texture]]
Croissants contain yeast, ''[[Saccharomyces cerevisiae]]'', which is incorporated during predough formation. When oxygen is abundant, the yeast breaks down sugar into carbon dioxide and water through the process of [[Cellular respiration|respiration]].<ref>{{Cite web|url=http://www.bakeinfo.co.nz/Facts/Bread-making/Science-of-bread-making/Rising-fermentation-|title=Rising (fermentation) |publisher=Baking Industry Research Trust |website=www.bakeinfo.co.nz|access-date=2016-12-14|url-status=live|archive-url=https://web.archive.org/web/20161220163539/http://www.bakeinfo.co.nz/Facts/Bread-making/Science-of-bread-making/Rising-fermentation-|archive-date=20 December 2016}}</ref> This process releases energy that is used by the yeast for growth. After consuming all of the oxygen, the yeast switches to anaerobic [[fermentation]]. At this point, the yeast partially breaks down sugar into [[ethanol]] and carbon dioxide. Once {{CO2}} saturates the dough’s aqueous phase, the gas begins to leaven the dough by diffusing to preexisting gas cells that were incorporated into the predough during mixing.<ref name=":0" /> Yeast action does not produce new gas cells, as the immense pressure required for a single {{CO2}} molecule to create a new gas bubble is not physically attainable<ref>{{Cite book|title=Principles of cereal science and technology|last=Carl|first=Hoseney, R.|date=2010-01-01|publisher=AACC International|oclc=457130408}}</ref>

In order to ensure the flaky texture of the croissant, it is important to balance the yeast activity with [[steam]] production. If the yeast overproduces {{CO2}}, then the well-defined layers may collapse.<ref name=":1" /> During the baking process, this would cause steam to escape too early from the bread, reducing dough lift and flakiness of the final product. Thus, to offset the negative effects of yeast on layer integrity and dough lift, croissants usually contain fewer layers than other puff pastries.

===Baking===
[[File:La parisienne unbaked croissant.jpg|thumb|rightUnbaked dough]]
During baking, the transient [[gluten]] network turns into a permanent network.<ref>{{Cite journal|last1=Goesaert|first1=Hans|last2=Slade|first2=Louise|author-link2=Louise Slade|last3=Levine|first3=Harry|last4=Delcour|first4=Jan A.|date=2009-11-01|title=Amylases and bread firming – an integrated view|journal=Journal of Cereal Science|series=Special Section: Enzymes in Grain Processing|volume=50|issue=3|pages=345–352|doi=10.1016/j.jcs.2009.04.010}}</ref> At higher temperatures, intermolecular [[Disulfide|disulfide bonds]] form between glutenin molecules, as well as between [[gliadin]] and [[glutenin]]. With more bonds being made, the gluten network becomes more rigid, strengthening the croissant’s crumb texture. Additionally, the baking process significantly stretches the dough layers due to the large macroscopic deformation that occurred during fermentation’s dough lift.<ref name=":0" />

Starch undergoes [[Starch gelatinization|gelatinization]] as a result of baking.<ref name=":3" /> Prior to baking, starch granules absorb a small amount of water at room temperature as it is mixed with water to form predough. As long as the dough’s temperature stays under the gelatinization temperature, this granule swelling is limited and reversible. However, once the baking process begins and the dough is exposed to temperatures above the gelatinization temperature, [[amylopectin]] crystallites become more disordered inside the starch granules and cause an irreversible destruction of molecular order.<ref name=":0" /> At the same time, [[starch gelatinization]] actively draws water from the gluten network, further decreasing the flexibility of the gluten. Currently, the extent of [[amylose]] leaching and granular structure distortion during the baking of croissants is still unknown.

Roll-in fat gradually melts as the temperature in the oven increases. Some of the melting fat can migrate into the dough, which could then interfere with gluten protein crosslinking.<ref>{{Cite book |title=Ullmann's Encyclopedia of Industrial Chemistry|last1=Sievert|first1=Dietmar|last2=Hoseney|first2=R. Carl|last3=Delcour|first3=Jan A.|date=2000|publisher=Wiley-VCH Verlag GmbH & Co. KGaA|isbn=9783527306732 |doi=10.1002/14356007.a04_331.pub2|s2cid=137346105 }}</ref> The fat phase also contributes to dough lift through gas inflation, which will be described next.

Water is converted to [[steam]] during the baking process, which is the main factor behind the leavening of the dough. The water for steam production comes from both the dough layers and the roll-in fat. As the fat melts, the continuous oil phase is no longer able to stabilize the water droplets, which are then released and converted to steam.<ref>{{Cite journal|last1=Borwankar|first1=R. P.|last2=Frye|first2=L. A.|last3=Blaurock|first3=A. E. |last4=Sasevich|first4=F. J.|date=1992-01-01|title=Rheological characterization of melting of margarines and tablespreads|journal=Journal of Food Engineering|series=Rheology of Foods|volume=16|issue=1|pages=55–74|doi=10.1016/0260-8774(92)90020-7}}</ref> Although the exact mechanism of steam entrapment is still unclear, it is likely a result of both steam expanding inside each dough layer and steam migrating to oil layers, where it inflates gas bubbles. The steam migration to oil phase is likely due to the smaller pressure differential required to inflate a bubble of steam in liquid fat than in solid dough.<ref name=":0" /> As the concentration of steam increases between dough layers, the increased pressure causes the dough to lift. During the entire baking process, only half of the water vapor contributes to dough lift, as the other half is lost through micropores and capillaries of interconnected dough layers.

===Storage===
The effect of [[gluten]] proteins during cooling and storage is still unclear. It is possible that gluten proteins influence croissant firming through the loss of plasticizing water, which increases the stiffness of the gluten network.<ref>{{Cite journal|last1=Bosmans|first1=Geertrui M.|last2=Lagrain|first2=Bert|last3=Ooms|first3=Nand|last4=Fierens|first4=Ellen|last5=Delcour|first5=Jan A.|date=2013-05-15|title=Biopolymer Interactions, Water Dynamics, and Bread Crumb Firming|journal=Journal of Agricultural and Food Chemistry|volume=61|issue=19|pages=4646–4654|doi=10.1021/jf4010466|pmid=23631677|bibcode=2013JAFC...61.4646B |issn=0021-8561|url=https://lirias.kuleuven.be/handle/123456789/422718|access-date=5 February 2019|archive-date=25 July 2018|archive-url=https://web.archive.org/web/20180725014504/https://limo.libis.be/primo-explore/fulldisplay?docid=LIRIAS100198&context=L&vid=Lirias&search_scope=Lirias&tab=default_tab&lang=en_US&fromSitemap=1|url-status=live|url-access=subscription}}</ref>

Starch plays a major role in the degradation of croissants during storage. [[Amylopectin]] retrogradation occurs over several days to weeks, as amorphous amylopectin chains are realigned into a more [[crystalline]] structure.<ref name=":0" /> The transformation of the starch causes undesirable firmness in the croissant. Additionally, the formation of the crystal structure of amylopectin requires the incorporation of water. [[Retrogradation (starch)|Starch retrogradation]] actively draws water from the amorphous gluten network and some of the amorphous starch fraction, which reduces the plasticity of both.<ref name=":0" />

Water migration influences the quality of stored croissants through two mechanisms. First, as previously stated, water redistributes from [[gluten]] to [[starch]] as a result of [[Retrogradation (starch)|starch retrogradation]]. Secondly, during the baking process, a moisture gradient was introduced as a result of heat transfer from the oven to the croissant.<ref name=":0" /> In fresh croissants, there is high moisture content on the inside and low moisture content on the outside. During storage, this moisture gradient induces water migration from the inside to the outer crust. On a molecular level, water is lost from the amorphous [[starch]] fraction and [[gluten]] network. At the same time, water diffuses from the outer crust to the environment, which has less moisture.<ref>{{Cite journal|last1=Gray|first1=J.A.|last2=Bemiller |first2=J.N.|date=2003|title=Bread Staling: Molecular Basis and Control |journal=Comprehensive Reviews in Food Science and Food Safety|volume=2|issue=1|pages=1–21|doi=10.1111/j.1541-4337.2003.tb00011.x |pmid=33451240|issn=1541-4337|doi-access=}}</ref> The result of this redistribution of water is a firming up of the croissant, caused by a decrease in starch plasticity and an increase in gluten network rigidity. Due to the presence of large pores in croissants, moisture is lost to the environment at a faster rate than bread products.<ref name=":2">{{Cite journal|last1=Roca|first1=Elisabeth|last2=Guillard |first2=Valérie|last3=Guilbert|first3=Stéphane|last4=Gontard|first4=Nathalie|date=2006-03-01|title=Moisture migration in a cereal composite food at high water activity: Effects of initial porosity and fat content |journal=Journal of Cereal Science|volume=43|issue=2|pages=144–151|doi=10.1016/j.jcs.2005.08.008}}</ref> As such, croissants generally become harder in texture at a faster rate than breads.

Fat also affects the quality of croissants in storage. On one hand, an increased amount of in-dough fat has been found to correspond to a reduction in crumb hardness immediately after baking.<ref name=":0" /> This is likely attributed to the high-fat content of croissants, as increased fat levels decrease moisture diffusion.<ref name=":2" /> On the other hand, although roll-in fat softens the croissant’s initial crumb, its effect on croissant hardness during storage is still unclear.