7) Fermented Cocoa, Tea and Coffee

Question 1

what are 2 methods of processing coffee beans?

Answer 1

dry and wet

Question 2

describe dry process of coffee beans

Answer 2

• beans are dried in the sun where microbial fermentation occurs (by enzymes secreted by bacteria, yeasts and pectinolytic molds which breakdown the pulp)
• sugar and flavours from the pulp are absorbed by the bean
• results in “natural” coffee

Question 3

describe the wet process of coffee bean fermentation

Answer 3

• 5 to 7 days of fermentation
• allows pulp around cherries to soften and separate; enhances acidity and provides floral aromatics
• results in” washed coffee”

Question 4

what are the steps in dry process (coffee)?

Answer 4

1. partial dehydration of pulp layer during ripening
2. harvest of fruit
3. fruit is spread out and sun dried

Question 5

what are the steps in wet process (coffee)

Answer 5

1. mature beans are de pulped
2. fermentation step to convert mucilage into water soluble products which are removed by washing
3. beans are sun or mechanically dried

Question 6

what MO are involved in wine fermentation?

Answer 6

molds
yeasts
LAB
Gram-neg

Question 7

what is the function of fermentation of the coffee cherries?

Answer 7

to prepare fruit for commercial use; causes degradation of the mucilages around the parchment skin which gives the bean a better appearance

Question 8

mucilages are mostly composed of _____

Answer 8

pectin; thus, the MOs involved must have pectinases

Question 9

when is the coffee fermentation over?

Answer 9

when mucilaginous tissues changes from viscous to liquid

Question 10

what is the function of using a starter culture in coffee fermentation?

Answer 10

• to speed process and improve coffee quality

Question 11

what are kona coffee beans?

Answer 11

• very expensive

- involves Erwinia dissolvens

Question 12

what is civet coffee

Answer 12

produed by consumption of ripe coffee cherries by the civet

• undergoes fermentation in GI tract
• animal excretes hard coffee beans

Question 13

what are the 2 functions of fermentation of cocoa beans for chocolate?

Answer 13

1. remove mucilaginous pulp surrounding the cocoa seed and to facilitate drying
2. induce biochemical transformations within the bean that lead to color, aroma and flavor precursors

Question 14

is the cocoa bean pulp anaerobic or aerobic?

why is this?

Answer 14

anaerobic; favours growth of yeast for fermentation (converts CHO to ethanol + CO2)

Question 15

what are the steps of cocoa bean fermentation?

Answer 15

1. pulp favours yeast growth: converts CHO to ethanol + CO2
2. yeast produces pectinolytic enzymes to degrade pectin; allows air in
3. air and ethanol favours LAB, which ferments CHO into lactic acid (homoferm) or lactic acid, AcOH, EtOH, CO2 (heteroferm)
4. AAB starts to take over due to higher availability of O2, ethanol and organic acids. AAB oxidizes EtOH to AcOH, which causes death of the cocoa bean (marks the end of fermentation)

Question 16

what marks the end of cocoa bean fermentation?

Answer 16

when AAB oxidizes EtOH into AcOH, which causes embryo death

Question 17

heterofermentative LAB uses what as a terminal electron acceptor?

what occurs when this compound is reduced?

Answer 17

fructose

when fructose is reduced, it generates mannitol (biproduct)

Question 18

which sugar is the best competitor at the beginning of the cacao bean ferm rxn?

Answer 18

glucose which is used by yeast

glucose not used by yeast will be fermented by LAB into lactic acid, AcOH, CO2, EtOH

Question 19

why is bean death critical for cocoa fermentation?

Answer 19

1. death allows cellular membranes to leak and permit enzymes and substrates to react to form flavour compounds
2. germination uses up the sugars and will not use valuable components of the bean

Question 20

what digests purple anthocyanins?

Answer 20

glycosidases

results in bleaching of the purple which releases more reducing sugars to participate in flavor development

Question 21

are purple cocoa beans desirable?

Answer 21

they are less desirable;

more pigments present = glycosidases did not breakdown many purple anthocyanins. Thus, there are less reducing sugars to use for flavour development

Question 22

describe the function of polyphenol oxidase in cocoa fermentation

when does it become active?

Answer 22

• responsible for browning
• reduces astringency and bitterness associated with the unfermented polyphenols
• becomes active when O2 can penetrate the bean in the final stages of fermentation

Question 23

what compounds are responsible for browning in cocoa fermentation?

Answer 23

polyphenol oxidase
catechins
lecuocyanidins

Question 24

is germination desirable in chocolate? what about in beer?

Answer 24

yes in beer brewing

no in chocolate

Question 25

how does the production of flavour and color compounds in fermentation affect the polyphenol and antioxidant effects?

Answer 25

higher flavour properties = lower polyphenol and antioxidant contents

Question 26

describe the drying and storage of cocoa beans after fermentation

Answer 26

• after fermentation, beans have 40-50% moisture content
• for safe storage, moisture must be 6-8% (or else mold growth may occur)
• dried beans can be stored for 3-12 months
• cocoa quality can change during storage (eg. slow oxidation and acid loss can occur)

Question 27

define kombucha

Answer 27

beverage obtained by fermenting tea with a microbial consortium composed of bacteria and yeasts

Question 28

what does SCOBY stand for?

Answer 28

symbiotic culture of bacteria and yeast

Question 29

what is a SCOBY? what does it contain?

Answer 29

 symbiosis that inhibits growth of potentially contaminating bacteria
 contains mixture of yeasts, AAB and LAB

Question 30

what does fermentation in kombucha lead to?

Answer 30

production of cellulose pellicle due to activity of certain Acetobacter sp.

Question 31

what is the most efficient yeast for kombucha fermentation?

Answer 31

Sc

Question 32

what is the dominant bacteria in kombucha ferm?

Answer 32

AAB; since aerobic bacteria can use alcohol as a substrate to produce acetic acid

Question 33

describe the cellulose production in kombucha

Answer 33

• bacteria synthesizes uridine diphospho-glucose (UDPGLc) which is a cellulose precursor
• each cell has pores (aka complex terminals) for extruding cellulose out of their membrane
• cellulose produced maintains at air/medium interface
• membrane thickness increases by new cellulose generation
• eventually, SCOBY will become dormant due to insufficient nutrients and O2

Question 34

what are sources of biological hazards in kombucha fermentation?

Answer 34

• between the boiling step until pH 4.2, pathogenic bacteria can outgrow SCOBY and cause contamination
• mold can also grow

Question 35

what are sources of chemical hazards in kombucha fermentation?

Answer 35

overfermentation: resulting in excessive AcOH production, which causes low pH which can leach out chemical contaminants from container