week 7 - MICROSCOPY, bio plastics, & finalization for bread project

During week 7, we were given time to work on our project Tuesday. For the final project, I have been researching the grain: wheat. During this week I looked further into the science of fermentation in bread. I found that fermentation is an anaerobic biological process that converts sugars and starches into simpler substances. In baking, it causes yeast and bacteria to convert sugars into carbon dioxide, among other things. This is what causes the dough to rise. 

In bakery products, fermentation is a complex series of biological reactions that allow dough to leaven. It is carried out by strains of Saccharomyces cerevisiae yeast, wild yeast and lactic acid bacteria (LAB). These microorganisms start by consuming simple sugars in the flour and generated by amylase. This produces CO2 and other compounds, which are responsible for the unique flavor and texture of bread.3 The process starts once yeast/LAB is added to the flour and water, either as individual ingredients or preferments. It continues through early stages of baking where the yeast/LAB is inactivated by heat. The fastest rate occurs during proofing and oven spring stages.

There are different microorganisms and fermentation types that have been used in bread dough. For example there are 3 examples: alcoholic fermentation also known as yeast, lactic fermentation/lactic acid bacteria (LAB), and lactic/lactic acid bacteria (LAB).

The table above explains the three types found in bread including the application, reaction, and the common used microorganism.

I also researched that the ideal pH fermentation in bread is primarily acidic to slightly acidic (4.5-6.5)

Additionally, I also found that ideal temperature ranges from 95-113F. Where at lower temperatures the fermentation slows down while higher temperatures produce an excessive acid buildup. 

  • Relative humidity (RH%): ideally between 50% and 90%.
  • Carbon source: LAB and yeast feed on monosaccharides and disaccharides.
  • Sugar level: 2.0–10.0%. Higher levels can negatively impact microbial activity due to osmotic pressure. Residual unfermented sugars are necessary during baking for proper crust color development.
  • Salt level: up to 2.5%. Higher levels exert considerable osmotic stress on yeast cells.
  • Water content: Absorption levels of 50.0% or higher, based on flour weight, are optimal. Higher levels lead to faster/uncontrollable yeast activity.
  • Yeast/LAB levels: The higher the yeast/LAB level, the shorter the total fermentation time required to mature the dough.

Futhermore, I looked into blogs that talked about the ideal fermentation of bread. There are multiple types of yeast including fresh yeast, active dry yeast, and instant yeast.

Fresh Yeast (a.k.a. Cake or Block Yeast): Fresh yeast has the highest moisture content of the three varieties. This extra water means it's bigger, which makes it easier to measure. Also, since the yeast hasn't been rendered dormant through processing, it has more leavening power than active dry or instant yeast. Some people swear that it tastes better than other commercial yeasts as well, but I've noticed no differences in taste between fresh yeast and the others. Its chief draw-back is that since the yeast is in an active state already, it will spoil and die faster than active dry or instant, giving it a short shelf-life, generally not more than two weeks.

Active-Dry Yeast: Of the three types of commercial yeast available, active dry has the longest shelf-life—in a sealed container in the fridge it will keep for years. For a home baker, this makes active-dry yeast a good choice. However, the manner in which it's processed means that many of the yeast cells are already dead at the time they are added to the dough, i.e. you need to use more than the other two varieties to get the same rise. For doughs that are very heavily yeasted, some people find that the yeast debris in active-dry creates undesirable flavors. It also needs to be reactivated in water—i.e. bloomed—prior to being added to the dough. If you're impatient, like me, this annoys you even though it isn't a big deal and probably shouldn't.

Instant Yeast: Instant yeast requires no blooming and activates more quickly than active dry. This means that it can be added directly to our dough and we can be on our way. Also, it has a relatively long shelf life, and that shelf life can be extended by keeping it refrigerated. For a home baker, I believe instant yeast is the ideal choice.

The blog also explained that more fermentation means tastier bread. In the most technical, terms fermentation is an anaerobic reaction (meaning it happens in the absence of oxygen) that the yeast performs after respiration, which is aerobic and requires oxygen. In bread baking, the word proofing most commonly refers to the final rise dough undergoes, which takes place after being shaped into a loaf, and before it is baked. In practice, however, the words proof and fermentation are sometimes used interchangeably. What's important to realize here is that shaping dough affects its physical form, but doesn't impact its internal chemistry—the processes and chemical reactions at work during our bulk and final rises are the same.

Today in class we explored microscopy and were able to view a various sorts of objects like ants, skin texture, and even fabric. Shown below is an image displayed on the screen of the microscopy. Microscopy is the technical field of using microscopes to view samples & objects that cannot be seen with the unaided eye (objects that are not within the resolution range of the normal eye).

Citations

https://bakerpedia.com/processes/fermentation/

https://www.ifst.org/lovefoodlovescience/resources/raising-agents-biological-fermentation

https://www.seriouseats.com/how-to-make-and-proof-bread-dough

https://www.themeateater.com/wild-and-whole/learn-cooking-technique/the-basics-of-bread-fermentation

https://academic.oup.com/jmicro