Chapter 18

Question 1

vinegar

Answer 1

• Acetic acid bacteria oxidize ethanol to actic acid- strict aerobes, this is not fermentation
  
  • Ethanol = acetaldehyde=acetic acid
    ACETOBACTER: used in all commercial applications, very efficient but in the absence of alcohol, it will oxidize acetic acid to CO2 and H2O - some ethanol must remain to prevent this

Question 2

brewing

Answer 2

1. Sieved malt crushed and fet into Mash tun
   
   2. Crushed malt (grist) stirred in hot liquor to form a mash
   3. Mash sent into a copper and boiled with hops 60-90mins
   4. Spent hops collected from liquid
   5. Cooling
   6. Yeast added and fermentation takes place
   7. Ale is allowed to mature in conditioning tanks and placed into casks

** key factors: water, malt, hops, yeasts and condition of fermentation (temp,time)

Question 3

malting and mashing

Answer 3

• Grains contain starch that cannot be digested by yeasts
  
  • Grains (barley) are allowed to germinate, producing amylase = MALTING
  • The grains are then dried and crushed = MALT
  • Malt is then soaked in warm water (65C) for 1-2h = MASHING. The amylase degrades starch to fermentable sugars (glucose and maltose)
    The mash is then filtered = WORT

Question 4

boiling

Answer 4

• Hops is added to the wort. Wort is boiled for 1-2 hours (near sterilization)
  
  • Hops gives flavor and bitterness. It also has antimicrobial properties and prvents lactic acid bacteria from growing in the final product
  • Commercial beer= filtered
• Cooled to 20C

Question 5

fermentation

Answer 5

• Yeast is added:
  
  1. Larger: saccharomyces carlsbergensis (bottom yeasts, 6-12C)
  2. Ale: saccharomyces cerevisiae (top yeasts, carried up by CO2 during fermentation, 14-23C)
     - Polishing: filtration, carbonation, pasteurization, …
     Light beers: yeasts manipulated genetically so they can use all the sugars in the wort

Question 6

distilled alcohol beverages

Answer 6

• Similar to beer making process but hops is not added. Different grains can be used:
  
  1. VODKA: wheat, rye or potatoes
  2. GIN: grains or starchy product + juniper oil and other flavor ingredients
  3. RUM: sugar cane (molasses)
  4. BRANDY/COGNAC: wine
  5. WHISKIES: malt brews
     - Alcohol is distilled
     - Aged, diltued with water
     Flavor ingredients are added
  • Whiskies: malt brew (scotch), other cereals (corn in the US). Wort is not boiled, mixed fermentation of added yeasts and resident lactic acid bacteria
  • Factors:
    1. Water
    2. Resident lactic acid bacteria
    3. Source of cultivar of the barley
    4. Shape of the still
    Ageing in wood cask

Question 7

kombucha: fermented tea

Answer 7

• Can be made with any type of tea (black tea tends to work best)
  
  • How to make Kombucha:
    1. Steep tea bags/leaves in boiling water
    2. Let cool to RT
    3. Strain tea/remove bags
    4. Add sugar
    5. And mother or SCOBY (symbiotic culture of bacteria and yeast)
  • Acetobacter and saccharomyces
    6. Transfer to jars and let ferment for 7-10 days
    Can add lots of extras for flavouring: herbs, spices, honey, fruit

Question 8

food spoilage

Answer 8

• Food spoilage: any change in the apperance, smell, taste that makes it unacceptable to the consumer. MAY still be safe to eat, not necessarily a health hazard
  
  • In north america, 10-20% of the foods are not suitable for consumption because of spoilage, up to 50% in developping countries
    Wide variety of microorganisms can cause spoilage: molds, yeasts, bacteria

Question 9

factors that affect food spoilage

Answer 9

• Types of microorganisms involved
  
  • Extent of growth of the microorganisms
  • Moisture content of the food
  • Temperature
  • pH
  • Availability of oxygen
  • Chemical composition and physical state
    Surfaces VS insides, grinding distributes the surface contaminant

Question 10

moisture content

Answer 10

• All microorganisms need water
  
  • Availability of water to microorganisms: water activity (aw)
  • Solutes dissolved in water reduce availability of water to microorganisms (vapor pressure decreases)
  • Fresh food: aw higher than 0.95
  • Aw of some foods:
    1. Maple syrup: 0.9
    2. Salted meats: 0.85
    3. Jams: 0.75
    4. Honey: 0.54
    5. Noodles: 0.5
    6. Cereal: 0.2
  • Moisture content: amount of bound water and free water in a sample, quantitative amount in a sample
    Water activity: amount of free water in a sample, a measurement of the energy status of the water in a system (qualitative)
  • Most spoilage microorganisms can grow to an aw as low as 0.9
  • Aw less than 0.9: most bacteria and yeasts are unable to grow. Many molds can still grow
  • Aw less than 0.8: only specialized organisms can grow:
    1. XEROPHILES (dry environement, low osmolarity)
    2. OSMOPHILES (high osmolarity: high sugar)
    3. HALOPHILES (high salinity)
    Staphylococcus aureus grows at aw high than 0.83

Question 11

temperature

Answer 11

• Crucial factor influencing spoilage
  
  • Hot foods should be kept above 60C
  • Cold food should be kept below 4,5C
  • Psycrophiles (grow best at low Temp)
  • Psychrotrophs (able to grow at low Temp)
  • Most pathogens do not grow at 4,5C except: YERSINIA ENTEROCOLITICA, LISTERIA MONOCYTOGENES, CLOSTRIDIUM BOTULINUM
    Microorganisms can survive for extended periods of time at 4C, if the temp. Is the temp. Is then allowed to increase, microorganisms can resume growth. (freeze/thaw cycle is risky)

Question 12

pH

Answer 12

• Most foods are neutral or acidic
  
  • Bacteria:
    1. Many grows at a pH as low as 5
    2. Lactic acid bacteria at pH 4
    3. Very few bacteria able to grow below pH 4
  • Molds and yeasts:
    1. Many can grow at pH 4 and lower
    Main spoilage organisms in acidic food (below pH of 4.5)

Question 13

oxygen

Answer 13

• Required for mols and many aerobic bacteria and yeasts
  
  • Excluding oxygen is a good sttrategy to prevent spoilage of food (vacuum packaging, canning, modified atmosphere). Also reduces oxidation of the product
    Some yeast and many bacteria can grow under anaerobic conditions; can cause swelling of the package (CO2 production): dont buy swollen packages!!

Question 14

chemical composition

Answer 14

• Nutrients available determine the types of organisms that grow
  
  • Enzymes produced and secreted will determine the type of foods that the microorgansims can use
  • Meat: high in proteins and fat. Requires proteases and lipases - proteolytic and lipolytic microorganisms: bacteria and mols. Under anaeroic conditions: mostly bacteria
    Vegetables: high in starch, cellulose, pectin, Fruits: high in sugars and pectin. Requires saccharase, cellulase, pectinase- saccharolytic, cellulolytic and pectinolytic microorganisms (bacteria, yeasts, molds)

Question 15

effect of moisture on bacteria, yeasts, molds

Answer 15

High: molds, yeasts, bacteria
Low: molds, yeasts

Question 16

effect of temperature on bacteria, yeasts, molds

Answer 16

Less than 10degree: molds, bacteria
Moderate: molds, yeast, bacteria
Higher than 40degree: only bacteria

Question 17

effect of acidity on bacteria, yeasts, molds

Answer 17

High acidity (pH less than 4,5): molds and yeasts
Low acidity (pH highr than 4.5): yeast, molds, bacteria

Question 18

effect of oxygen on bacteria, yeasts, molds

Answer 18

Present: yeast, molds, bacteria
Absent: yeasts, bacteria

Question 19

effect of proteins, carbohydrates and fats on bacteria, yeasts, molds

Answer 19

Proteins: molds (+/-), bacteria
Carbohydrate: molds, yeasts, bacteria
Fat: molds, bacteria

Question 20

wine

Answer 20

• Must= crushed grapes
  
  • Metabisulfite is added to kill wild yeasts
  • Sugar and organic acids may be added depending on the final product
    S. CEREVISIA + S. ELLIPSOIDEUS: rsistant to metabisulfite and tolerate 12-14% alcohol
    T. DRY WINE: all sugar is fermented
    SWEET WINE: some sugar is left or added after fermentation

Question 21

brie + camembert

Answer 21

• Unwrapped
  
  • Mixture of mold (PENICILLIUM) and bacteria (BREVIBACTEIRUM) that are spread on the SURFACE of the curd
  • Ripening in curing room (high humidity)
  • 1-5 months
  • PROTEASES secretd by the microorganisms is responsible for the softening of the cheese
    Good sanitary practice = requires so cheese not contaminated

Question 22

blue and roquefort

Answer 22

• Ripening is mainly du to the mold PENICILLIUM ROQUEFORTII
  
  • Spores from the mold are mixed with the milk (or the curd)
  • Small holes are drilled in the curd before wrapping
  • 3-6 months
    The mold grows in the holes and produces spores (blue)

Question 23

cheddar, swiss, gouda

Answer 23

• Wrapped (cheescloth)
  
  • CHEDDAR: ripening involve LACTIC ACID BACTERIA only
  • Longer ripening = higher acidity and sharpness
  • SWISS = PROPIONIBACTERIA produce propinonic acid + acetic acid (flavor) and CO2 (bubbles)
    OKA: pressed curd is brine, surface is washed frequently, growth of GEOTRICHUM

Question 24

cheese - RIPENING

Answer 24

• Ripening leads to changes in texture, consistency, and flavor
  
  • Due to specific microorganisms added with the starter culture or spread on the surface of the pressed curd
    Some of the ripening is due to the LACTIC ACID BACTERIA, RENNIN or other enzymes

Question 25

cheese - CURDLING

Answer 25

• Starter cultures of lactic acid bacteria are added to the milk:
  
  1. Microorganisms ferment lactose, produce lactic acid
  2. Promote development of the curd (precipitated proteins, fat and other suspended material) and whey (supernatant)
     - Rennin (enzyme) can be added to the culture
  3. Cleaves casein which results in curd formation (rennin or lactic acid bacteria work)
     Whey is drained off: starting material for other processes (whey powder), or discarder (high BOD, must be treated like sewage)
     - Curd is then heated (temp. Depending on the final prodct): more whey is expelled and the crud becomes more solid
     - Salt may be added: flavor, promotes extraction of water, inhibits growth of spoilage organisms
     Packaging (fresh cheese), or other processes: pressing, brining, ripening

Question 26

milk products

Answer 26

• Milk naturally contains lactic acid bacteria, but is usually pasteurized to remove potential pathogens. Desired microorganisms are then added back to give the final product
  
  1. YOGURT:
     - cultures of STREPTOCOCCUS THERMOPHILIS and LACTOBACILLUS BULGARIS are added and incubated at 42C
     - The acid denatures casein (milk protein) which results in thcikening
     - Other microorganisms are sometimes added (BL, BIFIBACTERIUM ANIMALIS)
  2. CHEESES: hundreds of microorganisms may be involved. Raw milk cheese may contain pathogens. 2 basic steps:
     - CURDLING: lactic acid bacteria precipitate the proteins = curd
     RIPENING: lactic acid bacteria + other microorganisms = flavor

Question 27

salami

Answer 27

• Made with ground pork and or beef
  
  • Mixed with other ingredients:
    1. Salt, sugar, spices, yeast
    2. Sometimes a starter lactic acid bacterial culture is added
  • Mixture is added to casing and allowed to cure:
    1. The preservation of food by addition of salt and drying
  • Warm (25C), humid (95%), conditions for 1-3 days
    Transfert to cool (12-18C), and humid (70-80%_ conditions and dry sausages for 6-10 weeks

Question 28

sauerkraut and pickles

Answer 28

• Cabbage is simply shredded and salted (final concentration of 2.2-2.8% NaCl, restricts growth of spoilage microorganisms). Microorganisms are naturally present on cabbage:
  
  1. LEUCONOSTOC MESENTEROIDES: lactic acid, flavor compunds, killed when acidity reaches 0.7-1%
  2. LACTOBACILLUS PLANTARUM: lactic acid only, increases acidity to 1.6-1.8%
  • PICKLES:
  • Use natural microflora
    Kill natural flora and use pure culture of PEDIOCOCCUS CEREVISIA and LACTOBACILLUS PLANTARYM (also sed to produce fermented sausages, salamie andbologna)

Question 29

most commons microorganisms

Answer 29

1. LACTIC ACID BACTERIA: gram positive, aerotolerant anaerobes, rods or cocci
   
   • HOMOFERMENTATIVE: fermentation yields primarly lactic acid (pickles, sauerkraut)
   • HETEREOFERMENTATIVE: fermentation yields lactic acid AND a variety of flavorful compunds (fermented sugars such as salami, fermented milk products)
   • Lactic acid reduces food spoilage and improve storage qualitues (brings th pH down)
   • Flavor compunds produces by different organisms give each product its distinctive taste

YEASTS (alcohol beverages): variety of SACCHAROMYCES strains