Exam Questions Grape/Wine Composition Flashcards

Question 1

Q

Polyosids in grapes and wines:
a) Describe the possible composition of the ‘Lateral Neutral chains of pectins’, that are mainly linked to the residues of rhamnose from RG-I?

b) Describe the molecules being the ‘Lateral Neutral chains of pectins’, that are mainly linked to the residues of rhamnose from RG-I?

c) Give 3 relevant aspects of the presence of polysaccharides in wines.

Answer

A

a)
-Arabinanes
-Galactanes (less quantity)
-Arabinogalactanes type I (AG-I)
-Arabinogalactanes type II (AG-II)
-or only some monosaccharides (arabinose, galactose, xylose)

b)
-Arabinogalactanes type I (AG-I)
-Arabinogalactanes type II (AG-II)

c)
Polysaccharides in Enology

i) Protector Colloids : protein haze inhibition, inhibition of the potassium bitartrate

ii) Membrane filtration: polysaccharides

iii) fining agents: chitin-glucan

Question 2

Q

Explain the copigmentation of anthocyanins and the following types: intramolecular, intermolecular, self-association and metal complexation.

Answer

A

Copigmentation: pigments and other noncolored organic components form molecular bonds.

-Stabalizes the anthocyanin

-enhances BOTH color intensity (hyperchromic effect) and the shifting to longer visible maximum wavelength (bathochromic).

Intermolecular: anthocyanin weakly binds to compounds such as flavonoids, phenolic acids and alkaloids (flavonoids and polyphenols)

Intramolecular: acyl group in acylated anthocyanin interacts with the anthocyanidin of the anthocyanin, linked by the sugar component

self-association: the copigment is the same anthocyanin that is being copigmented. The color is more intense than can be expected.

metal complexation: metallic cation that modifies the absorption spectra by affecting the distribution of the unlocalized electrons. Intense effects with + charged alkaline earth metals and poor metals (+ 2-+3).

Question 3

Q

Indicate 3 organic acids from grapes and 3 from the fermentative process, describing their main properties and influence in wine.

Answer

A

Grapes: tartaric, malic, citric

tartatic: freshness, unstable, percipitates with K
malic: harsh acid, unstable, metabolized into lactic acid
citric: freshness, unstable, increases diacetyl during MLF, metabolized into acetic acid and diacetyl

AF: Pyruvate, succinic, D/L lactic

Pyruvate: Color stability, ALF
glyceropiruvic fermentation
Glucose => Glicerine + Piruvic acid

Succinic: Salted and bitter flavour
Lactic: stable, softer than malic,
Acetic acid: vinegar

Question 4

Q

Discuss and describe the general evolution of condensed tannins during grape ripening in the different parts of the grape cluster (seeds, skins, pulp, stems)? What are the possible enological implications of this?

Answer

A

Seeds: after the formation of the seed, the tannin is moderate and decreases slightly, but stays moderate the entire time

Skins: Tannins are very high and then decrease as berry ripens to a moderate level

Pulp: remain low throughout the entire maturation process

Stem: High before veraison, moderate at veraison, and continue to decrease with ripening. Lowest tannins when stems turn brown

taste in field for development, delicate processing for seeds, stem inclusion if ripe (not green)

Question 5

Q

On the Mineral compounds of grapes and wines,

a) What can be the exogenous origin of Ca2+ ?

b) Discuss the possible importance of zinc (Zn) in Enology?

c) How can Cd be a contaminant in wines?

d) What can be the exogenous origin of SO42- ?

e) Discuss the possible importance of copper (Cu) in Enology?

Answer

A

a) Exogenous origin of Ca cation Ca2+: concrete tanks, deacidification with
calcium carbonate CaCO3 or calcium sulfate CaSO4, bentonite, filtrarion materials

b) Zn importance:
toxic level low = 5mg/L, zinc has an infinity to proteins in mouth - correlation with zinc and astingency (increases astringency)
located in skins and seeds, longer maceration increases zinc
zinc can also cause protein haze

c) Cd = Cadmium contamination: contact with metals, atmospheric pollution. fermentation decreases its content. max 10um/L, root (radicular) absorption

d) exogenous (outside) origin of sulfate SO4 2-: SO2 oxidation, addition CaSO4 deacidification, addition ammonium sulfate (NH4)2SO4, pesticides

e) importance of Cu: Cu and the reducted SO2, H2S can bind together creating CuS. CuS + proteins = haze.
-co-factor in oxidation
-CuSO4 can be used to eliminate off flavors related to sulfur compounds.

Question 6

Q

How would you describe the grape skin and seeds condensed tannins with reference to:
a) mean polymeration degree (mDP)
b) esterification by gallic acid
c) percentage of prodelphinidins?

Answer

A

Grape skin condensed tannin
a) mDP: 27 - 45
b) gallic acid: 2.7 - 6%
c) % prodelphinidins: 13 - 64 (depending on the variety)

Seed condensed tannin
a) mDP: 3 - 16
b) gallic acid: 13 - 30%
c) % prodelphinidins: non existant

CHRISTINA’S ANSWER
The mean degree of polymerization refers to the monomeric units (+ = catechin, - = epicatechin) bound together via polymerization to form polymers. The number of monomeric units is directly related to the perception of tannins; around 5 - 11 monomeric units is the peak intensity of the astringency perception.

mDP
catechin and epicatcechin
(how soft tannins are)
Polymerization degree; seeds ~ 3 - 15, skins 27 - 45 meaning seed tannins are
more perceived since they land more regularly in the 5 - 11 monomeric unit perception threshold

GALLIC ACID (antioxidant power)
Skins have lower number of galloylated subunits, seeds have more

gallic acid is considered the most important phenolic acid because it is the precursor for hydrolyzable tannins

PRODELPHINIDIN
gallocatechin, epigallocatechin:
(antioxidant)
Seeds have none (only procyanidins) And skins ~varietal dependent but contain both procyanidins and prodelphinidins(13-64)

3 ways mDP changes over time and perceived tannins decrease
Polymers of condensed tannins can break down into smaller monomers, becoming less perceived
Polymer chain becomes too large due
to polymerization and precipitate out of solution
Condensed tannins bind to anthocyanins and precipitate out of solution

Question 7

Q

On the mineral compounds of grapes and wines:

a) what can be the exogenous origin of K (Potassium) in wines?

b) discuss the importance of Pb (Lead) in Oenology.

Answer

A

a) exogenous origin K: bentonite, de-acidificants, KMBS
endogenous: grapes, tartrates

b) Pb importance: carcinogen, metal, contamination metal, fungicide, atmosphere, soil.

percipitates during AF in S form, absorbed by yeast/bacteria, combines with polysaccharides RG-II in body and acts as fiber (removes it) - decreases assimilation in the intestines

Question 8

Q

What kind of glucids (small sugars, oligossacharides and polyssacharides) might we find later in a wine, with a grape origin? Can you justify your comments?

Answer

A

Monosaccharides/small sugars
-fructose as residual sugar, as glucose gets metabolized first
-glucose and fructose in sweet wines

Polysaccharides:
-AGP (II) +AG(I)+AG(II)+RG(II)

Oligosaccharides:
derived from degredation of cell wall polysaccharides (arabinose, ramnose)

Not all sugars are fermentable by the yeast

Question 9

Q

Discuss the metabolic origin of sugars derived compounds formed during alcoholic fermentation, the factors that influence their synthesis and their impact on wine quality.

Question 10

Q

Describe the different ways to prevent the volatile phenols in red wines

Answer

A

-limit lag phase by LAB inoculation or co-inoculation
-clean winery/tanks/hoses
-top barrels regularly
-rack barrels often
-fine/filter
-be at molecular SO2 (0.4-0.6mg/L) or FSO2 > 15mg/L
-keep barrel room cool
-steam barrels
-test areas for
-proper nitrogen to prevent sluggish fermentation where Brett could take over
-pick for lower pH
-ferment until dry
-train staff to taste

Question 11

Q

Give some criteria for yeast selection to meet the challenges of global climate change (white and red wine production). Consider also different wine styles!

Answer

A

Red wine - osmotic pressure (higher sugar yeilds)
alcohol resistance, creating less alcohol

White wine
production of acids (lactic L. thermotolerance)
production of aroma compounds due to high temperatures reduces aromatics

Both
lower nitrogen requirements

Influence of climate change
-deficiency of minerals nitrogen
-stuck femrentation
- sulfur
-earlier aging
-atypical agine

Question 12

Q

Wine lactic acid may combine with potassium ions and get precipitate, reducing the wine acidity. a) True b) False

Question 13

Q

Proline amino acid can NOT be assimilated by Saccharomyces cerevisiae as nutrient.
a) True
b) False

Question 14

Q

According to most scientific studies, citric acid is present in grape juice in higher concentrations than malic acid. a) True b) False

Question 15

Q

ROLAND
1. Give the definition of “aroma precursor”:
a) Odorless molecule that could be either enzymatically or chemically cleaved to generate an aroma compound.
b) Odorless molecule that could be only enzymatically cleaved to generate an aroma compound.
c) Volatile molecule that could be either enzymatically or chemically cleaved to generate an aroma compound.
d) Volatile molecule that could be only enzymatically cleaved to generate an aroma compound.

Answer

A

a) Odorless molecule that could be either enzymatically or chemically cleaved to generate an aroma compound.

Question 16

Q

ROLAND
2. To which family do thiol precursors belong?

a) Varietal aromas
b) Fermentative aromas
c) Pre-fermentative aromas
d) Ageing aromas

Answer

A

ANSWER: a. Varietal aroma

But…….
fermentation aromas because they are liberated by yeast??

Question 17

Q

ONE or TWO answers can be correct
1. The alcoholic fermentation yield is:
a) The amount of alcohol produced per unit of time (h).
b) The relative amount of sugars that are converted into alcohol and CO2 in %.
c) The direct ratio between alcohol produced and sugar used
d) The ratio between amount of yeast biomass production and alcohol production

Answer

A

b) The relative amount of sugars that are converted into alcohol and CO2 in %.

Question 18

Q

ONE or TWO answers can be correct
During malolactic fermentation lactic acid bacteria form acetic acid
a) Only from sugars
b) From malic acid
c) From sugars and citric acid
d) From ethanol

Answer

A

c) From sugars and citric acid

Question 19

Q

The vineyard is the main source of Brettanomyces bruxellensis contamination
a) True
b) False

Question 20

Q

What are practical recommendations to monitor available nitrogen of botrytized must?
a) Adjust at 250 mgN/L and add at the beginning of alcoholic fermentation
b) Adjust at 190 mgN/L and add half of the dosage at the beginning of alcoholic fermentation and the second half after 1/3 of sugars degradation
c) Adjust at 140 mgN/L and add at the beginning of alcoholic fermentation
d) Adjust at 190 mgN/L and add at the beginning of alcoholic fermentation

Answer

A

d) Adjust at 190 mgN/L and add at the beginning of alcoholic fermentation

Question 21

Q

Yeast cells in nature are preferentially diploid. Which mechanism does not contribute to achieving this diploid state?

a) Axial budding pattern
b) Bipolar budding patter
c) Capability of mating type switching
d) Pheromone signal response

Answer

A

b) Bipolar budding patter

Question 22

Q

The Crabtree effect explains how yeast deals with sugar consumption. Which of the following statements correctly describes the Crabtree effect in S. cerevisiae?

a) The glycolytic flux is smaller than the respiratory flux
b) The glycolytic flux is equal to the respiratory flux
c) Fermentation in yeast takes place only in the absence of oxygen and is used to convert all sugars into ethanol.
d) The glycolytic flux is far greater than the respiratory flux. This results in overflow metabolism that is funneled through fermentation. Fermentation will take place already at low glucose concentrations even in the presence of oxygen.

Answer

A

d) The glycolytic flux is far greater than the respiratory flux. This results in overflow metabolism that is funneled through fermentation. Fermentation will take place already at low glucose concentrations even in the presence of oxygen.

Question 23

Q

How is the formation of esters, higher alcohols and hydrogen sulphide mainly influenced during alcoholic fermentation by a low concentration of yeast assimilable nitrogen (< 150 mg/L N) in the grape must?

a) esters increase, higher alcohols increase and hydrogen sulphide increases
b) esters decrease, higher alcohols decrease and hydrogen sulphide decreases
c) esters decrease, higher alcohols increase and hydrogen sulphide increases
d) esters increase, higher alcohols decrease and hydrogen sulphide decreases

Answer

A

c) esters decrease, higher alcohols increase and hydrogen sulphide increases

Question 24

Q

When does it make sense to add nitrogen in the form of ammonium salts (e.g. diammonium hydrogen phosphate (DAP)) during alcoholic fermentation?

a)	only at the end of alcoholic fermentation in the maximum permissible amount of ammonium salts and if a sluggish or stuck fermentation occurs
b)	after one third of alcoholic fermentation in the maximum permissible amount of ammonium salts
c)	half of the maximum permissible amount of ammonium salts in the middle of alcoholic fermentation and at the end of fermentation if a sluggish or stuck fermentation occurs
d)	at the beginning or in one or two additions during the first third of alcoholic fermentation, depending on the amount of assimilable nitrogen in the grape must, and taking into account the maximum permissible amount of ammonium salts

Answer

A

d) at the beginning or in one or two additions during the first third of alcoholic fermentation, depending on the amount of assimilable nitrogen in the grape must, and taking into account the maximum permissible amount of ammonium salts

Question 25

Q

The condensed tannins of grape skins (proanthocyanidins):
a) Present high rates of esterification by gallic acid
b) Do not have in its composition prodelphinidins
c) Present high mean polymerisation degrees that can reach values of 80.
d) Do not have (+) – catechin in its composition

Answer

A

c) Present high mean polymerisation degrees that can reach values of 80.

Question 26

Q

ONE or TWO answers can be correct:
What is the relevance in Oenology of the GRP [Grape Reaction Product]?
a) GRP is a polysaccharide present in the cell hall of the skins
b) GRP is not a substrate of the grape tyrosinase
c) GRP has amino acids in its composition
d) Syringic acid can be at the origin of GRP

Answer

A

b) GRP is not a substrate of the grape tyrosinase
c) GRP has amino acids in its composition

GRP is a reaction product (oxidation product) of caftaric acid

Caftaric acid is oxidized by Tyrosinase creating o-quinones, then those o-quinones oxidize GRP

Question 27

Q

On the Mineral compounds of grapes and wines,
a) Ca2+ is a minor mineral of the wines
b) Na+ may be in relation to the salty taste of some particular wines
c) The origin of Cd in wines is mainly the grape
d) Cu doesn´t have any recommended legal limit in the wines, by the OIV

Answer

A

b) Na+ may be in relation to the salty taste of some particular wines

Question 28

Q

The mechanism of copigmentation with applications in enology is:
a) Intramolecular
b) Intermolecular
c) Self-association
d) Metal complexation

Answer

A

b) Intermolecular

Question 29

Q

Pyranoanthocyanins are not affected by SO2 bleaching because:
a) They have 2 pyrilium rings
b) of the substituents in the B ring
c) C4 is fully saturated with 4 bonds
d) of the bathochromic effect

Answer

A

c) C4 is fully saturated with 4 bonds

Question 30

Q

Formation of polymeric pigments is favored during barrel ageing by:
a) High pH
b) Potassium content
c) Low temperatures
d) Oxygen content

Answer

A

d) Oxygen content

Question 31

Q

Explain how the formation of non-volatile and volatile compounds are affected by the availability of nutrients and yeast metabolism during fermentation:
Higher Alcohols

Answer

A

Higher alcohols can be formed in two ways,
1: Ehrlich pathway when there is sufficient amino acids (AA > a-keto acid > aldehyde > HA) Come from amino acids
2: Biosynthesis pathway when there is NOT enough amino acids (Pyruvate > a-keto acid > aldehyde > HA)

-If there is an abundance of nitrogen, then there will be less HA produced.

-concentration: less than 300mg/L is positive, greater 400mg/L = negative

-examples:
3-methyl butanol 50-400mg/L,
2-methyl butanol 10 - 30mg/L,
2-methyl propanol 20-80mg/L

-Yeast strain has an affect on HA production; Hansenula anomala can produce even in the absence of fermentaion metabolism. Some native strains are known to produce more 2-phenylethanol (rose)

Colder ferment = less

Question 32

Q

Explain how the formation of non-volatile and volatile compounds are affected by the availability of nutrients and yeast metabolism during fermentation:
Esters

Answer

A

-formed in two ways
1. acetate + ethanol or ethanal
2. ethanol + fatty acid precursors

-catalyzed by enzyme alcohol acetransferase (ATT) which uses Acetly Coenzyme A and Alcohol as substrate.

-The higher the nitrogen in the must, the higher the formation of esters during fermentation

-higher temp, more active, more esters

-examples: ethyle acetate 30-80mg/L = fruity, greater 200mg/L = nail polish
isoamyl acetate 0.16 - 5mg/L banana, greater than 5mg/L bonbon candy

-yeast strain also has an affect on the production of esters as some native species are known to produce higher amounts

Question 33

Q

Which role plays the choice of yeast strain (S. cerevisae) to improve fermentation development and to avoid off flavors?

Answer

A

Lower sulfur compounds production,

Less nitrogen requirements,

High temperature tolerance
High alcohol tolerance

Fast start to fermentation to avoid

Yeast strains have different nutrient requirements, ethanol tolerance, temperature preference/tolerance, sugar metabolism, ability to create volatile compounds

Question 34

Q

What is the main cause for an over production of H2S during fermentation and the occurance of off-flavors in young wines?

How to prevent it?

Answer

A

-deficiency of nutients - nitrogen amino acids and vitamins
-yeast with insufficient Nitrogen will follow reducive pathway
-off flavors in young wines are 30% cork taint and 30% sulfide compounds from thiols and mercaptans

-intelligent vineyard practices (dont over use SO2)
-choosing yeast strain that doesn’t produce sulfur compounds
-adequate clarification (removal of lees after pressing and fermentaion lees contain H2S)
-Adequate amounts of nitrogen (YAN above 150mg/L)
-Adequate amounts of vitamins (B1 -

Question 35

Q

Which strategies should be used to avoid the formation of reductive notes?

Answer

A

-intelligent vineyard practices (dont over use SO2)
-choosing yeast strain that doesn’t produce sulfur compounds
-adequate clarification (removal of lees after pressing and fermentaion lees contain H2S)
-Adequate amounts of nitrogen (YAN above 150mg/L)
-Adequate amounts of vitamins (B1 - thiamine) (B5 pantothenic acid) and trace elements (glutathion and cystine)

Question 36

Q

Types of nutrients required by yeast

Answer

A

-Nitrogen (YAN): nitrogen of amino acids and ammonium nitrogen
-salts (without nitrogen) - what is this?
-trace elements: K, Ca, Mg
-vitamins (thiamin)

Question 37

Q

Amount of YAN recommended for sluggish ferments

Answer

A

150 mg/L (sluggish?)

Question 38

Q

Nutrient suppliments allowed and their limitations

Answer

A

-inorganic nitrogen: DAP and ammonium sulfate (100g/hL)
-vitamins: B1thiamine (0.06g/hL)
-yeast cell hulls (40g/hL): addsorb fermentation inhibiting fatty acids, adds stirils (for cell membrane)
-inactive yeast : deliver organic N

Question 39

Q

When is it recommended to add nutirents, why

Answer

A

At least twice; beginning of fermentation and at 1/3 sugar depletion

After 1/2 sugar depletion the nutrients can no longer be taken up by the yeast because alcohol prevents the cell from releasing H+. This release of H+ regulates the cell’s pH and its critcal for call homeostasis.

Malo?

Question 40

Q

B1-1: Describe the population dynamics of a yeast culture grown in YPD. Which stages occur? Compare this to a culture grown in grape must, particularly reflecting on
(i) cell numbers and alcohol production and
(ii) differential usage of glucose and fructose.

Answer

A

There are four stages of yeast cell population dynamins;
1. lag phase - this is within the first hour of two of innoculation
2. exponential phase - huge amount of growth in a short period of time, usually 2 hours
3. stationary phase - growth reaches a stable limit and continues at the same rate until
4. decline phase - cell death

(i) cell numbers in a YPD can live for longer if there is food present, but in a fermentation the environment is harsher and alcohol will slow down/stop nitrogen uptake without nitrogen growth, mitosis will slow and eventually the stress will turn into Meiosis

-there is a longer lag phase depending on the yeast??

-low numbers at beginning, exponential increase

-the culture grown in grape must follows the same pattern with one slight variation; the depletion of glucose is what initiates the stationary phase, but with this lack of glucose (which is preferred by the yeast) there is a decline in cell density temporarily, but then it is regained while the remaining fructose is consumed. The stationary phase cannot be continued after the depletion of sugars because fermentation provides energy for cell growth.

(ii) yeast are glucophylic and prefer to eat glucose first. Once the glucose is gone, the stationary phase begins and continues until most of the sugar is consumed. Any residual sugar will be fructose.

Question 41

Q

B1-2: Describe the microbial successions and microbial contributions during lambic beer
fermentation. Compare these to the must fermentations with respect to yeast biodiversity and the potential bacterial contribution (wanted and unwanted). Name the species that occur in both fermentation systems.

Answer

A

Lambic: water, malt, hops.
spontaneous fermented beer, ancestral method

ROSIE’S ANSWER
LAMBIC- Spontaneous fermentation, ancestral method, malt is left in the open air for wild yeasts to settle on surface SLIDE 23
-microbial successions occuring in four phases:
1. enterobacterial and wild (oxidative) yeast phase (with a limited growth of acetic acid bacteria)
2. an alcoholic or main fermentation phase performed by Sacc. Yeasts
3. an acidification phase due to the growth of lactic acid bacteria and acetic acid bacteria
4. a maturation phase with the growth of Brett yeasts and lacticacidbacteria

The microbial succession:
in the beginning of fermentation there is a growth wild yeast, acetic acid bacteria, cycloheximide resistant yeasts and yeast - which eventually out-competes them all.

After the yeast fermentation is in decline, acetic acid bacteria and lactic acid bacteria are used for acidification. Typically in wine fermentation, acitic acid bacteria is preferably avoided, and lactic acid bacteria is only used if malolactic fermentation is wanted. These acidifying bacterias can cause oxidation and lactic off flavors in wine.

The maturation of the lambic fermentation includes the cycloheximide yeast Brettanomyces and lactic acid bacteria. In winemaking Brettanomyces is viewed as a spoilage yeast and creatse volatile phenols producing off flavors in wine, but are appreciated in lamic beer

Question 42

Q

B3: the genus Saccharomyces contains currently eight species. Name at least three of them and describe
(i) their temperature growth maxima
(ii) which effect these temperature maxima have in terms of fermentation capacity at higher/lower temperature
(iii) hybrids formed within the genus (which ones, which species were involved, which beverages are fermented with these hybrids)?

Answer

A

S. cerevisiae
(i) 41 - 42 C
(ii) this is the highest fermentation temperature, allowing it to survive in fermentations and out-compete other yeast
(iii) S. cerevisiae x S. eubayanus = S. pastorianus - lager beer fermentation
S. uvarum
(i) 34 - 35 C
(ii) one of the lowest fermentable yeasts, allowing it to survive and function at low temperatures and out-compete those who cannot. This low temperature threshold can also be a negative - if vineyard temperatures are too hot, this yeast can be killed
(iii) S. eubayanus x S. uvarum = S. bayanus - for beer fermentation
S. kudriavzevii
(i) 33 - 34 C
(ii) one of the lowest fermentable yeasts, allowing it to survive and function at low temperatures and out-compete those who cannot. This low temperature threshold can also be a negative - if vineyard temperatures are too hot, this yeast can be killed
(iii) S. cerecisiae x S. kudriavzevii - wine and cider

Question 43

Q

B4: Describe the relationship between Saccharomyces cerevisiae and Vespa crabro (hornet wasp).
Which advantages does this interaction have for each organism? With this knowledge, how could you improve the biodiversity in a vineyard?

Answer

A

-S. cerevisiae and the Vespa crabro have a symbiotic relationship. The wasps eat yeast as a protien rich food and the yeast act as probiotic in the wasp stomach. In return, the yeasts mate and sporulate in the wasps stomach, are carried to fruit and enter the fruit as the wasps eat, and over winter in the queen.

-promote insect biodiversity with sections of native plants and natural habitat within the vinyard. Dont mow winter grasses to create insect hibernation habitats. No pesticides.

Question 44

Q

B5: Describe the life cycle of Saccharomyces cerevisiae. Which cell types do occur? Which properties do these cell types have - and which blocks? Look at all aspects of biology (budding, mating, sporulation) and assign ploidy (number of chromosomes) to the cell types at individual stages.

how yeast breeding can be used in improving yeast strain fermentation characteristics.

Answer

A

A yeast cell begins with a shmoo. Two cells, one a and one A, each form shmoos to mate with each other forming a zygote. This zygote is a diploid (2 chromosomes) and has DNA from the a and A. The yeast prefer to stay in the diploid phase and will multiply via mitosis with a daughter cell forming from a bud with exact duplication of cell and DNA.

When mating phase is initiated, the diploid cells go through meiosis - a division of cell DNA and creation of new cells through sporulation with only one set of chromosomes - haploid cells.

These new haploid cells then are then dividing by mitosis - an exact duplication of itself through budding. This duplication occurs until the shmoos are initiated by pheromones and a and A cells join together to form a zygote. Then the cycle begins and then it starts.

-isolate and use for fermentation and then use for future
-breed two different species and gain preferred genetics from the parents (hot and cold temp fermentation)

Question 45

Q

B6: Describe the budding patterns in Saccharomyces cerevisiae. How does budding lead to senescence? Which molecular features mark cellular senescence in yeast (and also in humans)?

Answer

A

The budding pattern is different in haploid and diploids. The haploids are polar, with all the buds forming on the same pole. The diploid cells are bipolar and have buds on either pole.

The mother makes a ring for each daughter cell. When the daughter separates the ring forms a keratin scar.

The accumulation of budscars leads to the senescening of mother cells. The mother cells only have so much room for the scars, after about 30 to 40 daughter cells, there is no room and the budding stops and the cell dies.

increased size, wrinkles, slower budding

molecular aging = DNA loops out of chromosomes and form circles. The older, the more circles - shown in yeasts and humans

Question 46

Q

B7-1: Describe three methods used to isolate pure yeast cultures.

Answer

A

streak plate method using inoculation loop. Streak using spatula on agar plate. Sanitize spatual each time, 1, 2, 3, 4 times on the same plate in small sections.
generate and plate serial dilutions. Use 6 test tubes and dilute the yeast solution by 10x each time until you 10-7.
falling row using a Drigalski spatula - use four plates and one spatula, wiping from one to the next without cleaning. less and less will be on the spatula by the last

Question 47

Q

B7-2: Emil Christian Hansen isolated the first pure culture yeast for lager beer production. Why was this important? What happened before that in the industry? What became after? Which other industries were influenced by this? Who, actually, was Julius Wortmann?

Answer

A

It was important because beer spoilage was very common. And isolating this beer culture meant that breeding could be regulated with tanks and more consistent, easier beer could be created and now at scale. After, other industries, such as wine and cider, started isolating their yeasts as well.

Julius Wortmann the creator of Geisenheim Yeast Breeding Station

Question 48

Q

B8: Describe three ways of preservation of yeast cultures and discuss positive and negative effects of each.

Answer

A

subculture method - multiplication of mother cultures - reduces mutations/contamination - need man power and reagents and minimize passages
deep freezing - liquid nitrogen or electric cooling -80C
freeze drying - freeze, dry to remove water, dry again, store 2-8C

Question 49

Q

B9: Describe the four phases of the yeast cell cycle. What happens in these four stages? Which cytoskeletal components are involved? Which two mechanisms are used to move the daughter nucleus into the daughter cell?

Answer

A

G1, S, G2, M

G1: growth of daughter cell

S: synthesis, emergence of daughter cell, DNA replication, duplication of spindle body

G2: growth of daughter cell, DNA replication check, prepare for division, organelle inheritance

M: mitosis, enolgation and alignment of spindle, movement of chromosomes to opposite poles of nucleus, movement of daughter nucleus into daughter bud, cytokinensis

The nucleus is moved via myosin motor protein along the actin cable pulled by the microtubule from the mother cell into the daughter. Anything inherited from the mother is moved this way; mitochondria, DNA, vacuole…?

Question 50

Q

B10/11: Describe the pheromone signal transduction cascade of Saccharomyces cerevisiae. Which parts are involved (genes, peptides, modules)? What is the result of the signalling (= cellular response) and which effector proteins are involved?

Answer

A

Yeast cell mating begins with the production of pheromones in stage G1 called factors. a cells produce a-factors and A cells procude A-factors. To receive these factors the cells have receptors for the opposite factor where the pheromones bond. Once bonded, he pheromone response continues to the G-Protiens and then to the MAP Kinase Cascade. After the cascade the Ste12 regulator of cell fusion and DNA transcription (and 180 genes) is activated and the Far1 regulator protein stops the cell cylce and begins the formation of the Shmoo

Question 51

Q

B12: Explain the Crabtree effect of Saccharomyces cerevisiae. Use the terms glycolytic, respiratory and fermentative flux. How did the Crabtree effect evolve over time? What are Crabtree negative yeasts? How do they deal with glucose?

Answer

A

yeast cells do alcoholic fermentation even when there is O2 around and there is presence of more than 2 g/L glucose, it is odd because they make more ATP when respirating and less during alcoholic fermentation. Very large glucose uptake and quick.

GF = RR - glucose/pyruvat through both GF & RR
GF = consumption of glucose, some yeast started to do it faster, over flow went to FF pyruvate ethanol and CO2

The first step in alcoholic fermentation is glycolysis where glucose and fructose are transformed into 2 Pyruvate, 2 ATP, and 2 NADH

Yeast prefer NADH to go back to NAD+ and the easiest way to do that is alcoholic fermentation (or glycerol)

Evolved: originally a low glycolic flux - ATP went to respiration. They evolved to take in more glucose = overflow. To manage the overflow, yeast started to produce ethanol - fermentation flux. Now S. cerevisiae have a high glycolic flux = ATP from glycolysis is used for AF and respiration is repressed.

Glycolic flux is regulated independantly of O2. respiration suppressed and NADH reduced through ethanol production

Ethanol pathway - no mitochondrial, so less enzymes used

Crabtree negative yeast use glucose for respiration produce CO2 and biomass, if O2 present they do respiration
-S.C. all crabtree positive

Question 52

Q

B14: Discuss the risks of spontaneous fermentation? Which precautions can be taken to limit the contribution of unwanted microbes to the fermentation end product?

Answer

A

-unknown/unwanted microbes
-spoilage lactic acid bacteria or spoilage yeast like Brett, presenting off flavors
-long start to fermentation
-stuck fermentation

Prevent:
-clean fruit with low pH
-SO2 after processing, biocontrol
-innoculation
-thermovinification

Question 53

Q

How to prevent acetic acid bacteria in wine

Answer

A

-strict aerobes, so prevent oxygen on wine
-clean winery
-correct additions of SO2 (molecular)
-*most critical during red wine making - must break floating cap
-SO2 at crush or bio protection
-keep barrels topped

Gluconobacter found in must uses glucose to make AA

Acetobacter found in wine and uses ethanol to make AA

Question 54

Q

What are the advantages and disadvantages of the co-inoculation of S. cerevisiae and lactic acid bacteria

Answer

A

Advantages
-No lag phase, less susceptible to Brett
-shorter fermentation time, saves money

Disadvantages
-competition for nutrients
-LAB prefers sugar over malic, could stall yeast fermentation and prolong MLF
-creates diacetyl from citric acids and sugars

Question 55

Q

What quantities should be aimed for in order to obtain a balanced supply of YAN, in particular to achieve optimized aroma characteristics of the wines, and on which factors are theyalsodependent?

Answer

A

150 mg/L
above 350 increases ethyl acetate esters
below 150 sulfur compounds and H2S more likely

Temperature

Question 56

Q

Explain how the formation of non-volatile and volatile compounds are affected by the availability of nutrients and yeast metabolism during fermentation:
Volatile thiols/sulfur

Answer

A

Lacking in nutrients especsially nitrogen increases H2S production

Yeast metabolism of amino acids also causes sulfur compounds

Other sulfur compounds are bound volatile thiols, which are liberated by yeast metabolism during fermentation.

yeast strain as an effect on both

s-containing pesticides

Question 57

Q

Explain how the formation of non-volatile and volatile compounds are affected by the availability of nutrients and yeast metabolism during fermentation:
Terpenes

Answer

A

Terpenes are found in grapes in the free and bound form.

Yeast and bacteria metabolism both can release monoterpenes from sugar bonds (linalool)

Nirtogen deficience enhanses the production of terpenoids

Question 58

Q

Which facultatively pathogenic yeast occur within human body niches?

Answer

A

(41-51) Which facultatively pathogenic yeast occur within human body niches?

-S. cerevisiae is not a commensal (we are not the right habitat) with humans. How can Saccharomyces yeast, nevertheless, promote human well-being?

-Malassezia on the skin, hair follicles
-Candida albicans SLIDE 39 in the oral cavity, gut, vagina, skin

-S. cerevisiae decreases inflammation and intestinal colonization by Candida albicans, immune modulating, increases resistence against other microbialinfections

Question 59

Q

Explain the following terms:
WGD
Synteny
Petite cell
Grandecell

Answer

A

WGD: At some point in time S. cerevisae created a copy of all genes = more options in evolution. Spare genes = mre building blocks. Over time duplicates were kicked out, but some kept by evolution (3&13)

Synteny: conserved gene order on chromosomes from different species that are from a common ancestor
(useful to compare genes to see development over time)

Petite cell: mutant that is unable to synthesize cytochromes A and B due to a block in the aerobic respiration pathway. Much smaller than grand when grown on glucose

Grandecell: wild type respiratory sufficient colonies

Question 60

Q

What acid is increased by fungus

Answer

A

Gluconic acid and Mucic acid

produced: by oxidation of the aldehyde

Question 61

Q

What is the purpose of pumpovers

Answer

A

to homogenize the tank, mix the high pH (medium, low, high - from bottom to top), prevent acetic acid from growing on cap in oxygen environment

Question 62

Q

What is the yeast strain that produces lactic acid from glucose, and what are its adventages and disadvantages?

Answer

A

Lachancea thermotolerans
Low alcohol tolerance of ~ 10%
color up, aroma up,
acetic acid down, ethanol down

Question 63

Q

What are the two types of lactic acid and what causes them

Answer

A

D - yeasts
L - lactic bacteria and Lachancea thermotolerans

Question 64

Q

If your wine has 0g/L of citric acid, what does that mean

Answer

A

Lactic bacteria metabolize citric acid, so you have active bacteria

Answer 60

A

SO2, Lysozime, Chitosan

Answer 61

A

yeast produce it during fermentation
bacteria produce it during fermentation and after

Answer 62

A

-metabolizes malic acid into ethanol
-lactic acid not produced
-happens in mitochondria

Answer 63

A

Advantage: biological stability, decreases acidity, softens the wine, color stability

Disadvantage: increases pH, increase VA (small sugars into AA), N substances formed (histamines), ethyl lactate, diacetyl, loss of color

-0.34 tartaric

Answer 64

A

Sugars - Lactic acid & VA & Dextrane
Glycerine - AA, propionic & acroleine (bitterness)
Tartaric: AA, propionic, butiric, hydrogen, CO2,
Citric: Lactic acids & AA
Histidine - histamine
Scorbic acid - geraniol

Answer 65

A

Temp (min 18C),
pH (<3),
alcohol (max 15),
SO2 (max FSO2 10ppm)

When malic is close to 0g/L
-because the bacteria will continue metabolizing the next acid; citric, then succinic

Answer 66

A

Coumaric, caffeic, coumaroyl tartaric

-Etylphenol precursors
-In cinnamic series
-Esterified with an alcohol function of tartaric acid
-Naturally present in grape skin.
-Ascorbic acid constitutes a redox system in fruit juice,
protecting phenols from oxidation.

Answer 67

A

Stable: lactic, acetic
Unstable: tartaric, malic, citric… the rest?

Answer 68

A

Inorganic nitrogen:
Molecular nitrogen (N2). Ammonia salts (NH4)

Organic nitrogen:
Amino acids, Oligopeptides, polypeptides,
proteins, amide nitrogen, Biomines,
nucleic nitrogen, amino sugar and
pyrazines.

Answer 69

A

ionic compounds which, when dissolved in water, break up completely into ions. They arise by the reaction of acid and bases, and they always contain either a metal cation or a cation derived from ammonium NH4+.

Ammonia salts activate fermentation

Answer 70

A

1 Ammonium salts

#2 Glutamate & Glutamine
#3 Arginine
Others: Alanine, Serine, Threonine, Aspartate, Asparagine, Urea,

Answer 71

A

Proline.
Others: Glycine, Pirimidine, Lysine, Histidine, Thymine, Thymidine

Answer 72

A

Biogenic amines
-allergen
-origin: bacteria only
-limit: 2mg/L
-Prevent: SO2, lysozyme, chitosan
-Control: Select Lactic bacteria, Schizosaccharomyces, Lachancea thermotolerans
-Correct: unknown
Ethyl carbamate
-carcinogen, genotoxic
-origin: urea + lactic bacteria metabolism
-limit: 15um/L
-Prevent: N management, no malo
-control: urease enzyme, selected yeast/bacteria
-correct: unknown
Ochratoxin
-carcinogenic, neurotoxic
-origin: fungus, bacteria
-limit: 2um/kg
-Prevent: Vineyard phytosanitary control, biocontrol
-Control: Sorting, immunoaffinity
-Correct: maceration, fining agents, selected yeast, steril filter

Answer 73

A

Decarboxylated by Lactic Bacteria

AA Histidine -> Histamine
AA Tyrosine -> Tyramine
AA Ornithine -> Putrescine
AA Lysine -> Cadaverine

Answer 74

A

Total Nitrogen: Method Kjeldahl > 450 mg/l
YAN: Sorensen method > 150 mg/l
Relationship: TN = AN X 3

Ammonium ion:
Ammonia > 25 mg/l
Amino acids:
[Amino acids – Proline] > 100 mg/l

Answer 75

A

hyperchromic effect: due to decrease in pH, intensifies color (moves line up)

bathochromic effect: co-pigmentation, intense purple color (moves line to the right)

hypochromic effect: from SO2, loss of color (moves line down)

hypsochromic effect: not sure why (moves line left)

Answer 76

A

Coloured flavonoids absorbing between 400 and 600 nm depending on the substituyents at the aromatic rings.

pH
Hydratation
SO2
oxidative degree
Copigmentations

Answer 77

A

malvidin
delphinidin
peonidin
cyanidin
petunidin

Monoglucosides=Burgundy (highest in must)
3G: (-3-O-glucoside)

Acetilated anthocyanins = Magenta (cab, merlot)
3G6Ac: (-3-O-(6-O-acetyl)-glucoside)

Coumaroylated anthocyanins = Purple (grenache, temp)
3G6Cm: (-3-O-(6-O-p-coumaroil)-glucoside)

Answer 78

A

Musts: monomerics highest

Wine: bulging appearance, lower monomeric, highest acetilated (everything decreases as aging)

Old wine: peaks of courmarolylated

Botrytis: less of everthing

Answer 79

A

Formed during fermentation and aging

Malvadin + Pyruvate = Vitisin A
Malvadin + Acetaldehyde = Vitisin B

Stable against:
-Resistance to oxidative degradation
-SO2 bleaching (by having carbon bonds full)
-Less sensitive to colour changes by pH

Answer 80

A

colored polymers with at least 2 flavanoids - one being an anthocyanin

-need oxygen/acetaldehyde to gain color
-less sensitive to pH change than anthocyanins
-resistant to decolorization by SO2
-more orange/yellow in color
-bigger than monomeric pigments (blue/red color)

-in wine, the anthocyanins are displaced (progressively and irreversibly) by more stable polymeric pigments (50% of colour density in 1st year of aging)

Answer 81

A

Enzymes are proteins that catalyse chemical
reactions

-reduces the energy needed to form products)

Answer 82

A

pectinases, cellulases, and hemicellulases (GLYCOSIDASE, PROTEASE)

Enzymatic reactions
-cell wall degradations
-release of vacuole contents when fruit is crushed
-“maceration enzymes” favor the release of
cell wall skin tannins, can add more fullness/body

Answer 83

A

a. - enables lactic acid bateria to produce energy (ATP) thanks to proton/acid translocations during malolactic fermentation Yes
b. - leads to lactic acid and CO2 production and a rise in pH Yes
c. - leads to a stabilization of wine thanks to the removal of a substrate that stimulates bacteria growth Yes
d. - provides the bacteria energy through the direct ATP production by the malolactic reaction NO

Answer 84

A

Sulfites :
a. - have an efficiency that depends on pH since only non-ionized form can cross the plasma membranes of microorganisms -YES
b. - have an efficiency that depends on pH since it impacts on free and combined form of sulfites NO
c. - inhibit more efficiently lactic acid bacteria than yeast and acetic acid bacteria YES
d. - inhibit growth with the same efficiency of all microorganisms( bacteria and yeast) present in wines NO

Answer 85

A

c) Torulaspora delbrueckii produces low amount of acetic acid

Answer 86

A

primary metabolite = ethanol

secondary metabolite = esters, aldehydes, higher alcohols, sulfur compunds, terpenes

Factors: Nitrogen, temperature, yeast strain

More nitrogen = less higher alcohols, more esters, less sulfur compounds

Higher temperature = faster nitrogen use, more sulfur

Answer 87

A

Used to be considered spoilage yeast, now traits being re-evaluated

-phenotypic traits from both parents
-Better adaptation from mixing genomes (ferment at BOTH low and high temperatures)
-SC x SU = low production of acetic acid, liberate many volatile thiols
-less alcohol production, more esters in hybrids

Bioprotection with SC
-less SO2

Answer 88

A

Spontaneous risks
-unpredictable yeast, not consistant year after year
-delayed start of ferm
-limited ferment power
-formation of off flavors (acetaldehyde, biogenic aminces, acetic acid)
-more 2-phenylethanol (rose/honey higher alcohol) produced

Spontaneous advantage
-cheaper
-marketing

Inoculation
-basically the opposite of above
-select yeast for sertain purposes (lowering malic, increasing lactic)

Answer 89

A

There are three types of nutrient supplements; DAP, Vitamin B1 (thyamine), and yeast hulls.
DAP: 100g/hL
B1: 0.06g/hL
Hulls: 40g/hL
It is best to add nutrients at the early stages of fermentation and in two separate stages. First at the beginning and then the second at 1/3 sugar depletion. It should never be added al together in the beginning because you can produce too large of a colony and they might compete for nutrients at the end of the fermentation and stall. You also should not add after 1/2 sugar depletion because the yeast metabolism can no longer take it up because cell wall is damaged by alcohol and limits pathway of nitrogen in and H+ out. Without being able to release H+ out of cell - increase in pH = no good, so no more nitrogen in to maintain homeostasis

Answer 90

A

Malolactic fermentation is the metabolism of malic acid into lactic acid by lacid acid bacteria.
-softness to wine
-stability microbio
-loss of color but stability

LAB can also metabolize diacetyl and acetic acid from citric acid

Answer 91

A

-they need a lot of nutrients (especially amino acids and vitamins)
-micro aerophillic
-oenococcus <3.5 pH
-lacto & pedio >3.5 pH
-tolerate alcohol

LAB have a preference of food; sugars, malic, and then citric. MLF needs to be monitored, wine should be dry before starting and once all the malic is consumed it should be stopped with SO2 or lysozeme because if it metabolizes the citris it will create diacetyl or acetic acid.

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