The Science of Baking Pt. 1

Introduction

Have you ever wondered how exactly baking turns a soupy batter or a thick paste into a beautiful cake or cookie? Think no further, this article will soon explain what goes into the magic that is baking and some other cool facts.

How does science play its part?

Baking does a great job of showcasing just how prevalent science is to everyday activities. It combines chemistry, biology, and physics to create the decadent end product. The laws of physics apply to everything, but for baking, those laws are compounded with chemical reactions within ingredients and the processes of biology. The incorporation of many different edible chemicals like baking soda and baking powder to create a cake batter or dough causes reactions like tiny air bubbles forming that are trapped and cause rising. This is where biology also comes in with the culture of yeast as a leavening agent that provides carbon dioxide for bread to rise.

Role of Ingredients in Bake

Every single ingredient that goes into a baked good is there for a reason. Many people know from experience that forgetting to include even a single item on a baking recipe can end in total disaster. But what exactly is each basic baking ingredient doing?

Sugar and Fat

Many recipes will tell you to add the sugar and fat component, whether it be butter or ghee or oil, and there is a very specific reason for that. When sugar is added to butter, the sharp crystalline structure of the sugar slice the butter molecules and introduce air into the mixture. This is why creaming the sugar and butter before adding it to the other dry ingredients causes a lighter and fluffier outcome! Fat also adds that rich flavor by coating the gluten molecules so they do not combine as easily which also makes the product more tender.

Creaming of butter and sugar

Flour

Flour is made up by grinding raw grains or wheats or nuts to form a powder. The protein in the flour, gluten, works to form a web that traps air bubbles and allows the pastry to set in place. Basically, flour makes up the entire structure of the baked good and without it, the pastry would collapse! While the baked good heats in the oven, the starch in the flour sets in order to add and support the structure of the dish.

Chemical structure of starches in flour

Salt

Salt has many functions in normal cooking, but it does in baking as well! It enhances and strengthens the flavors in other ingredients to form the perfect balance. Salt also allows the gluten provided by the flour to form better as well.

Baking Soda

Baking soda, has a very special role in baking as well. It’s scientific name is sodium bicarbonate, and it is a crystalline salt. For the sodium bicarbonate to work it’s leavening magic, it can either be combined with an acidic component like buttermilk to cause an acid-base reaction or can be left to perform with just thermal decomposition in the oven.

This graphic shows the chemistry going on with baking soda

More to come…

As we can see, there is a lot of science that goes into perfecting a pastry. Without the chemistry, biology, and physics, it would be impossible to create any pastries or bread goodies. In the next article, we play with an at-home experiment of varying the type of fat used in one type of pastry and comparing the two different end products!

Sources

Babincáková, Mária. “Leavening Agents: The Chemistry of Baking Discovered with a Computer-Based Learning.” Journal of Chemical Education, vol. 97, no. 4, Apr. 2020, pp. 1190–1194. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&AuthType=ip,shib&db=eric&AN=EJ1250850&site=eds-live&scope=site.

Bodach, Vijaya. Baking a Cake. Perfection Learning, 2013. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&AuthType=ip,shib&db=nlebk&AN=650384&site=eds-live&scope=site.

Claire, Jillian, “The Chemistry of Baking” (2014). Senior Theses. 23. https://scholarcommons.sc.edu/senior_theses/23

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.