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DIY Field Notes

Behind the Baking: Leavening

November 5, 2022

Introduction

Welcome to the second installment of my Baking Science series! This time, I’m putting a variety of leavening agents to the test to see how they perform based on taste, texture, and overall look. I will be baking three loaves of bread: one using yeast, one using baking soda, and one using baking powder. I predict that the loaves of bread will all vary greatly from each other, but I am especially interested in finding how the baking soda and baking powder bread differ since a majority of the general population cannot distinguish the two.

What goes into baking beautiful bread?

Most kinds of bread come together with only six ingredients: flour, oil, water/milk, a leavening agent, sugar, and salt.

What’s a leavening agent and how does it work?

The word ‘leavening’, as defined by Oxford Dictionary, is a substance used in dough or batter to make it rise, such as yeast or baking powder. Without this key ingredient, it would be impossible for the bread to rise, resulting in a flat cracker. In order to create a good ole’ sturdy loaf of bread, a couple of essential chemical reactions need to take place in the oven. The first ingredient, flour, contains two proteins called gliadin and glutenin; when combined with water, these proteins transform into gluten. The chemical makeup of gluten shows that the molecules are chained together to create long chains- this allows the bread dough to be elastic and stretchy. This is also why the longer the dough is kneaded, the more elastic it becomes. The dough’s stretchy quality is super important in achieving the end loaf because of the way the leavening agent works. The agent causes a bunch of tiny gas bubbles to form in the dough either before or while it is in the oven. Ever watched a baking competition and heard the cast talk about ‘proving’ their doughs? I know I have! The proving process involves letting your dough rest and rise before it is put in the oven to bake. This step is integral when using yeast, but not necessary for baking soda and powder since they do their work in the heat of the oven.

Experiment

Three loaves. Three agents. One winner. Just kidding, but I will include which bread I enjoyed the most at the end!

Round 1: Yeast

Recipe: https://butterwithasideofbread.com/homemade-bread/

Round 2: Baking soda

Recipe: https://sallysbakingaddiction.com/no-yeast-bread/

Round 3: Baking powder

Recipe: https://www.recipetineats.com/sandwich-bread-without-yeast-quick-easy/

Observations and Opinions

Unsurprisingly, the bread that came out the best, in my opinion, was the yeast bread. This comes as no surprise because most of the breads that are sold in stores and that people generally think of are made with yeast. It’s hard to beat lightweight, airy feel of the yeast bread crumb. The baking soda bread was also delicious, but much much denser than the yeast bread. The baking powder bread was the weirdest- it was super heavy and stodgy and just not good. That might have been due to my error though, I may have overmixed it or kneaded it too much. The baking powder bread was so tough I didn’t want to cut a slice and eat it.

Final Thoughts

My favorite bread of the three was the yeast bread! The other breads honestly did not stand a chance against the tried and true yeast bread and I now know that I do not care for soda bread much. I would advise against making bread with baking powder, it was so hard for me to get it right but maybe some practice could improve it. Overall, it was super fun to test out these leavening agents and see them in their rising action.

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About Author

Ivana is currently an undergraduate at Georgia Tech studying computer science. On a day off, you may find her binge-watching her new favorite TV show, playing with her two dogs, or playing solitaire/doing a crossword.

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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.