Microbiology of Beer, Bread and CheeseTest 2, Spring 2015

Name___________________________________________

Part One: Answer 4 of the following 5 questions. Pay attention to the underlined numbers, and only list/state/describe that many. (20 points, each)

Question 1. All leavened breads, like the head on a good beer, are foams. Briefly state one role (each) that gluten, kneading and yeast play in the production of bread foam.

Question 2. Lactobacillus sanfranciscensis is a heterofermentative lactic acid bacterium that is found in many sourdough starters. Did you see evidence of this bacterium in your starter? Explain why you think so (or don’t think so), and then tell one important product that this microbe makes, and how it impacted your pizza dough.

Question 3. Native grains play a huge role in determining the types of bread that are made in a region. List two grains and then tell how the biological characteristics of each (including gluten content, seed hardness and ploidy, as appropriate) determine the type of bread originally made from that grain, and the type of cooking technology originally used.

Question 4. Unlike squirrels, humans do not necessarily find raw grains to be particularly palatable nor nutritious. List two characteristics of grains that make them unpleasant, lacking in nutrition, or even dangerous for us, and then briefly describe how each can be positively impacted by a bread-making process.

Question 5. You have just finished brewing a batch of beer, and have taken the following measurements: Original gravity (OG)= 1.038Final gravity (FG)= 1.012

Use the appropriate formula(s) from the list below to calculate the apparent amount of sugar that has been fermented into alcohol.

Alcohol by Volume (ABV) = (OG - FG) x 131.25Degrees Plato (°P) = (-463.37) + (668.72 × SG) - (205.35 × SG2)Real Extract (RE) = (0.1808 × °Pi) + (0.8192 × °Pf)Apparent Attenuation (AA) = 1 - [°Pf / °Pi]

Part Two Essay: All Students Must Answer This Question (20 points)

Although sourdough was almost certainly the first type of bread made by humans, "San Francisco" sourdough starter was first made famous by prospectors during the California gold rush in the mid 1800's. Prospectors were generally out in the wild for extremely long periods of time with no access to refrigeration or other modern amenities and fiercely guarded their starters

for backslopping. Long-term gold miners were called 'sourdoughs' and 'Sourdough Sam' is the mascot for the San Francisco 49ers NFL Football Team.

1) What is backslopping?

2) What sugar did the bacteria in these starters probably use? What about the yeast? Why was this sugar utilization important to the establishment of a stable sourdough starter?

3) List three biochemical products produced by the microbes in the sourdough starter and tell how each contributed to the flavor, taste and aroma of the final bread product.

4) What is caramelization and how did it impact the final bread flavor, aroma and appearance?