Chapter 11 Flashcards
yeasts
- unicellular fungi that reproduce by budding
- have no taxonomic standing, simply denotes a growth form
Dimorphic species of yeast
- shift from filamentous to yeast under certain environmental conditions (e.g. some jelly fungi, some human pathogens, some mushrooms, etc.)
What are Saccharomycetales
- “True yeasts” that undergo fermentation
What is fermentation?
- sugar + yeast= CO2, energy and alcohol
- Anaerobic respiration of food by microorganisms
- Release of energy from substrate/sugars in the absence of oxygen
What are the products of fermentation?
- Carbon dioxide, energy, and alcohol or various organic acids
What are the age old applications of yeast?
- Bread
- Wine/ Beer/ Spirits
- Cheese and Yogurt
What did Louis Pasteur hypothesize?
- that bacteria spoils wine
- Suggested that wine be heated to kill bacteria
- Hence: pasteurization of milk
Fermentation pros
- Extended shelf life (ex. Cheese)
- Eases Digestion (ex. Wild rice)
- New [better] flavors (ex. Chocolate)
Fermentation cons
- Can be unpredictable (i.e. bad bacteria win the battle)
- New [worse] flavours (ex. Mouldy bread)
Types of Fermentation
- Yeast fermentation
- Mold and enzyme fermentation
- Bacterial fermentation
Yeast fermentation
- Metabolic process that converts sugar to acids, gases, and/or alcohol
- it is anaerobic and takes place in the absence of oxygen
What is the formula for baking with yeast?
- flour + sugar + water + yeast = ethyl alcohol +CO2
- best temperature is at 27’C (warm)
- too much salt will ruin the process
What is the earliest processed foods?
- bread
Baking with yeast is a $__________ industry in the US.
- 16 billion dollar
Saccharomyces cerevisiae
- bakers yeast
Properties and characteristics for bread making
- Gassing power
- Flavor development
- Stable to drying
- Stable during storage
- Easy to dispense
- Ethanol
- Cryotolerant
How to make wine?
- fermentation of grapes that dates back to the Middle East
When does fermentation of grapes begin?
- after the grapes are crushed and yeast is added to it, once the yeast begins to digest the sugars present in the grape juice
Botrytis cinerea
- Latin for “grapes like ashes”
- bunching of the fungal spores and “ashes” the grayish color of the spore mass
- aka Noble Rot
Where is Noble Rot found?
- This species is ubiquitous
- it is found virtually everywhere plants are grown.
How does Noble Rot affect grapes?
- fungus causes grapes to lose water thus increase sugars, impart flavor, increase etoh = noble rot!
- more expensive wines
What is sake made from?
- made from rice, rather than from grapes, barley or corn
How is sake made?
- First koji mold such as Aspergillus oryzae, is used to convert starch in the rice to sugars
- Then fermented by other microorganisms, such as yeast (Saccharomyces) and lactic acid bacteria.
What is beer?
- An alcoholic beverage produced by the fermentation of sugar-rich extracts derived from cereal grains or other starchy materials.
How long has beer been made?
- since the dawn of civilization, where grain was grown beer was made
The first places to make beer were
- Sumaria
- Egypt
- India
- China
What does beer resemble?
- liquid bread
How did ancient brewers domesticate yeast?
- Selected yeast that made good beer
- Found it was important to make beers
Antonie van Leeuwenhoek
- Observed yeast in beer
Cagniard Latour
- found that the microbe is responsible for alcoholic fermentation
Justus von Liebig and Friedrich Wohler
- found that alcohol is produced by a chemical process in which dead and decaying yeast participated.
- Satired Latour’s theory in Annalen der Chemie
Latour’s theory in Annalen der Chemie
- was that a small animal which sips sugar through its snout, and excretes alcohol from its gut and carbonic acid from its urinary organ.
Louis Pasteur
- Discovered yeast was responsible for alcoholic fermentation
Emil Christian Hansen
- Developed pure culture technique
- Isolated pure cultures of brewing yeasts
Two types of brewing yeasts
- Top-fermenting (ale yeast, weiss yeast)
2. Bottom-fermenting (lager yeast)
Ingredients in beer
- Malted barley, cereal adjunct, hops, water, yeast
Hops
- Gives the spice of the beer, a flavoring agent that provides aroma and bitterness
- Flower (cone) of vine-growing plant, can come from Humulus lupulus, lupulin or Canabaceae
Mold and Enzyme Fermentation
- Break down cellulose thus grains easier to chew
- Add flavor and texture to cheeses (ex. blue)
Bacterial Fermentation
- Lactic Acid Bacteria (pickles, sauerkraut) 2. Acetic Acid Bacteria (vinegar)
- Carbon Dioxide Bacteria (Edam, Gouda, Swiss)
- Proteolytic Bacteria (cocoa, chocolate)
