WINE MICRO PART 2 Flashcards Preview

WSC307 WINE MICRO > WINE MICRO PART 2 > Flashcards

Flashcards in WINE MICRO PART 2 Deck (66)
Loading flashcards...
1

1.. Write concise notes about the role of spore forming bacteria in wine spoilage..

Bacillus and Clostridium .These organisms are distinctive because they are gram positive organisms that form spores which are visible by microscopy.Re-inoculation of wine by the former group resulted in increases in total and volatile acidity.Clostridium species have also been implicated in a form of spoilage involving the production of n-butyric acid (butyric acid taint). Their growth is restricted to high pH wines (> 4.0) or juices. Butyric acid (and other short chain fatty acids) is a major component of the volatile compounds from aromatic cheese such as parmesan.

2

2.. What media is used to select and differentiate acetic acid bacteria from wine.. Abbreviations are unacceptable..

Glucose Yeast Extract Carbonate Agar (GYC)

3

3.. Name two genera of acetic acid bacteria of relevance to wine production..


Lactobacillus and Pediococcus or Oenococus

4

4.. What are the three major functions of malolactic fermentation in wine??

Deacidification;
Increased microbial stability
Modification of flavour and aroma.

5

5.. Describe the oenological attributes that are desirable for commercial LAB starter cultures..

Tolerance of inhibitory compounds in wine, particularly ethanol (up to 15% w/v) and SO2 (at least 50 mg/L total SO2);
Ability to grow at low temperature (down to at least 15°C) and low pH (3.0);
Resistance to infection by bacteriophage;
Have a positive influence on the sensory properties of the wine ; and an absence, or minimal production, of spoilage compounds

6

6.. Write the equation that describes the chemical reaction that occurs during malolactic fermentation..

HOOC.CH2.COOH - CO2 + CH3.CHOH.COOH
L-malic acid - L- lactic acid

7

What causes spoilage with Acidification?

Excessive amounts of acetic acid and D lactic acid by homofermentative and heterofermentive LAB

8

What causes bitterness in wines

Glycerol is metabolised to form acrolein which reacts with anthrocyanins to produce a bitterness taint know as amertume

9

What causes Buttery taint?

Excessive production of diacetyl 1-4mg ok above 4mg is considered off.

10

What causes geranium off flavour?

Transformation of sorbic acid to sorbinol which forms the geranium off odour

11

What causes Histamine production?

Formed through decarboxylation of amino acids e.g hystamine,tyramine

12

What causes Manitol taint?

Formed through reduction of fructose by heterofermentative LAB

13

What causes mousy off flavour?

Production of 2 - acetyletrahydropyridines by heterofermantative LAB

14

What causes Ropiness?

Due to the development of a viscous character as oily or slimy (also known as la graisse)

15

What cause Tartaric Acid fermentation?

Tartaric acid is metabolised by species Lactobacillus to produce in part acetic acid resulting in increased volatile acidity

16

8. What are the 3 major end products of heterolactic acid fermentation??

CO2, lactic acid and ethanol/acetate

17

Influence of yeasts upon growth of Lactic Acid Bacteria during Winemaking..
Impact Brief description

Negative
Competition for nutrients during alcoholic fermentation
Production of inhibitory substances
(ethanol, SO2, fatty acids, anti-bacterial proteins)
Positive
Sedimentation of LAB
Release of nutrients during yeast autolysis

18

10.. How may malolactic fermentation have a detrimental impact upon red wine quality?

MLF is only good for dry red wines and not sweeter wines. Can cause Volatile phenol production. Can cause aromas of horse sweat , leather, asphalt, mould, medicine and smoke.

19

11.. Discuss the impact of juice clarification upon

Excessive clarification of must removes a significant proportion of the indigenous LAB population. Additionally, suspended solids removed during clarification are a source of nutrients that are stimulatory to LAB.

20

12.. Name 3 genera of lactic acid bacteria associated with wine production..


Pediococcus, Oenococcus, Lactobacillus

21

13.. What are 3 important sources of lactic acid bacteria in wine??

Vine leaves and the surfaces of grapes; Winery equipment; and (if relevant) Starter cultures added by the winemaker.

22

14.. Describe the relationship between lactic acid bacteria growth,ethanol tolerance and temperature..

Increased ethanol concentration decreases the optimal temperature for growth. Lactic acid bacteria belonging to Lactobacillus and Pediococcus have a higher maximum ethanol tolerance than Oenococcus oeni. In general, ethanol concentrations above 13% (v/v) limit the majority of LAB in wine.

23

15.. Describe the major biochemical pathways involved with the production of acetic acid in wine by acetic acid bacteria..

Two major pathways: (i) an oxidative pathway and (ii) a minor reductive pathway, both involving enzymes of the citric acid cycle. Qualitatively, acetic acid is the most important organic acid produced during the alcoholic fermentation. Pentose phosphate pathway (also known as the hexose monophosphate pathway)

24

16.. Describe wine production techniques that may control growth of acetic acid bacteria..

In wine composition, the most important component is oxygen for which the bacteria have an obligate requirement. During vinification where oxygen is essentially excluded, the populations of AAB decline. However, operations during conservation that expose the wine to oxygen can promote rapid growth of AAB. Such operations include transfers, pumping operations, and even storage in barrels where the penetration of oxygen through the wood is believed to be sufficient enough to support their survival.

25

What are some of the nutrients required by Oenococcus Oeni?

Vitamins
Nicotinic acid, thiamine, biotin pantothenic acid, pyridoxal
Component of co-enzyme complexes
Metal ions
Na+, K+, Mg2+, Mn2+
Enzyme co-factors, reaction with free oxygen radicals
Nucleic acid bases
Guanine, adenine, xanthine, uracil
Components of nucleic acid molecules

26

18.. How might the growth of Oenococcus oeni result in decreased wine quality?


Increased lactic acid bacteria production.

27

19.. Complete the following table of features of LAB of relevance to wine production.. The first section has been completed by way of example..

GENERA
MAJOR SPECIES
MORPHOLOGICAL
FERMENT TYPE
Oenococcus Heterofermentative
oeni
Non motile cocci
Pediococcus Homofermentative
oeni
Non motile rods
Lactobacillus Heterofermentative
oeni
Long and Slender rods

28

20.. Write concisely on the formation of dihydroxyacetone by acetic acid bacteria..

The formation of dihydroxyacetone is a distinctive feature of G. oxydans and A. aceti through their ability to oxidise glycerol. This reaction appears to occur only in grapes infected by AAB, particularly strains of G. oxydans. Must produced from infected grapes may contain

29

21.. Wine LAB may originate from three sources which are:

Vine leaves and the surfaces of grapes; Winery equipment; and (if relevant) Starter cultures added by the winemaker.

30

23.. You wish to encourage diacetyl production in a wine by growth of a selected strain of Oenococcus oeni . Briefly describe the wine management strategies,, including physical and chemical parameters,, that you should attempt to create in order to achieve maximum production of diacetyl..

Diacetyl has a characteristic flavour and aroma that may be beneficial or detrimental to quality depending on its concentration in wine. In general, a concentration of about 1 - 4 mg/L is considered to add a desirable ‘complexity’ to wine by imparting a nutty or caramel flavour. At concentrations of about 5 mg/L and above, diacetyl develops an intense buttery character in wine that is perceived as a fault.

31

24.. Ropiness arises from production of extracellular polysaccharide by certain bacteria.. Name two bacteria associated with ropiness wine spoilage.. Genus and species names required..

Ropiness’ refers to a condition where the wine develops an oily, viscous mouthfeel (sometimes also known as ‘slimey’ or ‘fatty’). The problem is related to the production of extracellular dextrins and other polysaccharides that modify the consistency of the wine.
Leuconostoc mesenteroides, Pediococcus damnosus

32

25.. Describe five desirable properties of an Oenococcus oeni starter culture for malolactic fermentation..

Tolerance of inhibitory compounds in wine
Ability to grow at low temperature (down to at least 15°C) and low pH (3.0);
Resistance to infection by bacteriophage;
Have a positive influence on the sensory properties of the wine
Absence, or minimal production, of spoilage compounds

33

26.. Discuss how pH influences the growth of Lactic Acid bacteria and consequently the biochemical end products of these organisms in wine

In wine pH the growth rate of Oenococcus oeni is faster as the pH increases, and over pH 3.6 growth of deleterious lactic acid bacteria is also likely to occur. As pH increases the rate of citric acid utilisation and acetic acid production is reported to increase. Laboratory studies have demonstrated that low pH favours higher diacetyl production, possibly arising from a slower growth rate.

34

27.. An increase in wine pH arises from malolactic fermentation (MMLF)) which potentially favours growth of spoilage organisms.. Paradoxically MLF brings about improved microbial stability.. Explain..

The primary factor affecting malolactic activity is pH. Malate degradation occurs fastest in the pH range of 3.0 - 4.5 which encompasses the range of pH values in wine. This is related to the fact that wine pH influences the internal pH of the cell. The increase in internal pH improves the activity of the malolactic enzyme as its pH optimum is near 6.3.

35

29.. Complete the following table of features of LAB with relevance to wine production..

Temperature manipulation
Adjustment of fermentation temperature Thermovinification
Clarification
Removal of suspended solids
Contact with yeast lees
Additions to wine
Acid adjustment

36

30.You wish to encourage malolactic fermentation (MLF) in wines without the requirement for addition of a starter culture.. Describe the wine management techniques that you would attempt to manipulate to favour MLF by indigenous organisms and provide reasoning for each practice..

Deacidification
The malolactic fermentation offers the winemaker an avenue by which this high acidity may be reduced.

Microbial Stability Of Wine

By allowing MLF to occur prior to finishing and preparation for packaging, winemakers hope to preclude its occurrence after bottling. Wines that undergo MLF in the bottle develop a haze and gassiness that would detract considerably from its value.
In this instance, further growth of these bacteria can be controlled by the actions of the winemaker. These treatments include pH adjustment (down), racking off lees, physical removal of microorganisms (by filtration), treatment with SO2, and storage at low temperature.
Flavour And Aroma Modification
By allowing MLF to occur prior to finishing and preparation for packaging, winemakers hope to preclude its occurrence after bottling. Wines that undergo MLF in the bottle develop a haze and gassiness that would detract considerably from its value. Malolactic fermentation may also have an impact on the fruit-derived sensory aspects of the wine, particularly the fruity and vegetative characters.

37

31.. Discuss the impact of juice clarification upon growth of Lactic Acid Bacteria in wine..

Clarification procedures actually remove a significant proportion of the indigenous (LAB population). Clarification also removes suspended solids that contain numerous nutrients that are stimulatory to LAB. These are probably the main reasons why MLF occurs with greater consistency in red wines (where fermentation is conducted on skins) than in white wines.

38

32.. List three sources of lactic acid bacteria in a winery..

Grape Vines and grapes
Winery equipment; and (if relevant) Starter cultures added by the winemaker.

39

33.. What impact may organisms belonging to the Actinomyces/Streptomyces group have upon wine quality? Where are do these organisms usually reside in a winery?

These organisms have been isolated from wines and corks and have been implicated as a source of cork taint, these bacteria may develop a distinctive musty aroma.

40

34.. You wish to encourage wild malolactic fermentation in a red wine that has the following parameters;; pH 3.75,, ethanol concentration 14.5%%vv//vv.. Describe the appropriate wine management aspects of this wine to produce complete malolactic fermentation with a desirable strain of a lactic acid bacteria whilst minimising or preventing growth of spoilage micro organisms..

Proper preparation of starter culture,correct choice of bacterial strain,high viable metabolic active population of LAB

41

35.. Growth of acetic acid bacteria generally requires the presence of oxygen (or another suitable electron acceptor)) for respiration.. Describe appropriate wine production techniques for the control of growth of acetic acid bacteria during all stages of the wine making process..

While the presence of oxygen is considered a requirement for the growth of most AAB, it is difficult to achieve this at all times during wine production. For example, oxygen is believed to penetrate the wood in barrels in sufficient quantities to support the survival of AAB. Additionally, the efficacy of SO2 in controlling AAB is questionable as there are conflicting reports as to the levels of SO2 required.

42

36.. Describe how the concurrent growth of yeast may affect growth (negative and positive aspects)) of lactic acid bacteria..

Negative
Competition for nutrients during alcoholic fermentation
Production of inhibitory substances
(ethanol, SO2, fatty acids, anti-bacterial proteins) Sedimentation of LAB
Positive Release of nutrients during yeast autolysis

43

37.. Describe the oenological attributes that are desirable for a commercial Oenococcus oeni starter culture..

Tolerance of inhibitory compounds in wine, particularly ethanol (up to 15% w/v) and SO2 (at least 50 mg/L total SO2);
Ability to grow at low temperature (down to at least 15°C) and low pH (3.0);
Resistance to infection by bacteriophage;
Have a positive influence on the sensory properties of the wine (see Topic 2); and
An absence, or minimal production, of spoilage compounds

44

38.. Describe the formation of bitter taint in wines.. Include in your answer some of the organisms responsible for this form of spoilage and the wine chemical parameters that would enable growth of these organisms to arise..

Bitterness taint, or amertume, is a rare form of spoilage.Central to the formation of bitterness taint is the degradation of glycerol by a dehydratase to produce 3-hydroxypropionaldehyde.This compound then undergoes spontaneous dehydration in wine to form acrolein. While acrolein itself is tasteless, it can react with phenolic components to produce the bitter taint. For this reason, red wines are more prone to this spoilage than white wines due to their higher phenolic content.

45

39.. Describe how the growth of Oenococcus oeni can lead to decreased wine quality?

Increased acetic acid production

46

42.. Name two species of Pediococcus and Lactobacillus that may grow in wine..

Pediococcus parvulas,damnosus ,
Lactobacillus brevis,plantarum

47

43.. Gluconobacter sp.. and Acetobacter spp.. are known spoilage organisms that may produce excessive quantities of acetic acid.. Which of these organisms is more likely to cause wine spoilage in packaged products and why is this so?

Acetobacter - Acetic acid bacteria (AAB) derive their energy from the oxidation of ethanol to acetic acid during fermentation.

48

44.. Write concisely on wine management strategies and their influence upon growth of Lactic Acid bacteria in wine..

Temperature manipulation
Adjustment of fermentation temperature Thermovinification
Clarification
Removal of suspended solids
Contact with yeast lees
Additions to wine
Acid adjustment

49

46.. Describe the potentially undesirable outcomes of growth of Oenococcus oeni in wine (regardless of style))..

Bitterness, buttertry taint/geranium, Histamine production, mousy/ Ropey aroma, fermentation of tartaric acid

50

49.. Discuss how pH influences the growth of Lactic Acid bacteria and consequently the biochemical end products of these organism s in wine..

Decreasing pH favours the growth of O. oeni, which predominates below pH 3.5. Other genera are favoured at higher pH.

51

50.. Describe wine production techniques that may control growth of acetic acid bacteria..

The major factors influencing the growth of AAB relate to wine composition (oxygen, ethanol, SO2, pH) and temperature of fermentation.In wine composition, the most important component is oxygen for which the bacteria have an obligate requirement.

52

53.. Write concisely about the formation of biogenic amines in wines..

The formation of biogenic amines occurs in wines containing strains of wine LAB that possess the necessary specific amino acid decarboxylases. Biogenic amines are significant contaminants in wine because they may elicit an allergic response (or cause other pathological symptoms such as hypertension) if present in sufficient concentrations. The most widely encountered biogenic amine is histamine

53

54.. Excessive clarification of juice may arise through employment of highly efficient technology such as centrifugation.. Describe what nutrients are likely to be decreased by excessive clarification,, how these specific nutrients impact fermentation if not present in sufficient quantities,, and what wine production strategies may be employed to correct deficient nutrient levels..

Excessive clarification of must removes a significant proportion of the indigenous LAB population. Additionally, suspended solids removed during clarification are a source of nutrients that are stimulatory to LAB. There is also evidence to suggest that tannin-protein complexes removed during clarification help to protect LAB from bacteriophages.

54

57.. Describe three wine production strategies that may assist in control of surface films and how each technique will influence growth of unwanted yeasts..

Completely filling the storage vessel with wine or by placing a nitrogen, carbon dioxide or argon headspace over the product.
Growth may also be controlled by a combination of low temperature and high ethanol concentration.
In cases where films have already developed, filtration of the wine is the most effective means of removal

55

58.. Describe how a wet yeast starter culture should be bulked up prior for use as inoculum for fermentation.. Provide in your answer the physical and chemical parameters that should be monitored and target specifications..

Preparation of ‘wet’ starter cultures involves propagating the culture up through successive stages (in increasingly larger tanks) until sufficient yeast numbers are available for inoculation into must. In the final stage of yeast propagation, the starter inoculum is usually about 1 - 3% of the final volume of the must (vol/vol).
A typical propagation process begins with transferring yeast biomass from an agar slant into sterile grape juice (100 mL). The pH of the juice should also be about 3.5 - 4.0 and supplemented with 2g/L diammonium phosphate. Ideally, no SO2 should be present to minimise stress on the young culture. Incubation at 25°C for 24 - 72 hours (preferably with shaking) under aseptic conditions should provide a vigorously growing pure culture. This culture is then used to inoculate a larger volume of must (generally 5 - 15 fold volume increase), and the process repeated until a sufficient volume of yeasts is prepared.

56

59.. During a regular inspection of ullaged 20kL tanks you notice one tank of your mid - range price point red wine with a thin oily film and a slightly crusty surface.. You request chemical analysis of top and bottom samples which are presented below.. What wine management strategies should be put into place to ensure this wine does not deteriorate any further in quality??

Candida causes this.Completely filling the storage vessel with wine or by placing a nitrogen, carbon dioxide or argon headspace over the product.
Growth may also be controlled by a combination of low temperature and high ethanol concentration.
In cases where films have already developed, filtration of the wine is the most effective means of removal

57

60.. The recent vintage has been extremely hot resulting in overripe fruit and high alcohol concentrations.. During the vintage a small parcel of Grenache was harvested at 14.8 Baumé and fermented to dryness.. Despite the hot vintage malic acid levels are still over 1 g//LL but MLF starter culture was not inoculated into this w ine near the end of primary fermentation as is standard practise in the winery.. Blending is not an option with this product and you now have a wine with nearly 15.0%% v/vv ethanol requiring MLF.. Describe how you should manage this wine and MLF starter culture to ensure complete MLF..

Tolerance of inhibitory compounds in wine, particularly ethanol (up to 15% w/v) and SO2 (at least 50 mg/L total SO2);
Ability to grow at low temperature (down to at least 15°C) and low pH (3.0);
Resistance to infection by bacteriophage;
have a positive influence on the sensory properties of the wine An absence, or minimal production, of spoilage compounds

58

62.. Write concisely on wine spoilage due to Dekkera spp..

Dekkera has been implicated in the formation of other unpleasant off-flavour compounds such as an apple or cider-like aroma, ‘mousy-off-flavour’ (substituted tetrahydropyridine compounds) and phenolic taints

59

63.. In a large commercial winery the final wine production processes for a white blended wine involves adjusting sugar concentrations to final specifications (77.0 g//LL)) using grape juice concentrate approximately 2 days prior to online filtration (00.45 μm)) during packaging.. Sulphur levels (330 ppm free));; sorbate (1150 ppm)) and pH (33.20)) are added or adjusted in accordance with wine specifications immediately prior to packaging.. Five weeks post packaging this product develops a haze and spritz.. Microscopy re veals the presence of numerous yeast cells.. Discuss the likely yeasts species that may be involved in this spoilage problem.. Include in your answer possible sources of contamination and pertinent winery management strategies to prevent future recurrences of the problem..

Dekkera
Wines that undergo MLF in the bottle develop a haze and gassiness that would detract considerably from its value.
These treatments include pH adjustment (down), racking off lees, physical removal of microorganisms (by filtration), treatment with SO2, and storage at low temperature.

60

64.. A small batch of chardonnay wine has the following chemical parameters:: Alcohol 13.5%% (vv//vv));; pH 3.1,, TA 8.5 g//LL.. You are having difficulty getting malolactic fermentation to occur in this wine.. Describe the management techniques that can be applied to this parcel of wine to ensure MLF is completed..

pH Manipulation 3.2 to 3.4
Temperature - maintenance of temperatures between 16°-25°C, with an optimal level at about 20°-22°C
Sulfur dioxide - the presence of SO2 is inhibitory to LAB, so an ideal situation would be have no SO2 present at the end of the alcoholic fermentation.
Lees contact - this will encourage the occurrence of yeast autolysis which releases nutrients that are stimulatory to LAB.
Clarification - excessive clarification of must removes a significant proportion of the indigenous LAB population. Additionally, suspended solids removed during clarification are a source of nutrients that are stimulatory to LAB.
Contact with skins - extended contact will allow time for increased extraction of stimulatory substances from grape skins.

61

65.. Red grapes are mechanically harvested at night seven days following a hail storm that has caused about 10%% of the fruit to be damaged by splitting.. No sulfur was added to the harvest bins by mistake and due to mechanical breakdown the grape bins are left on a truck for eight hours prior to weighing and de-stem//crush.. Describe microbial flora that is most likely to be the present in the grapes prior to inoculation with a starter culture and how these organisms will influence the final composition of the wine made from these grapes..

Indigeneous yeast would be present such as Saccharomyces cerevisiae . Species of molds are also present, including those belonging to the genera Aspergillus, Alternaria, Botrytis, Cladosporium, Penicillium, Plasmopora, and Unicinula.

62

66.. You wish to make a varietal white wine that exemplifies the expression of grape variety and wine making skills.. What production and microbiological aspects of the yeast strain should be considered in choosing an appropriate starter culture?

Desirable MLF is said to contribute complexity to the sensory profile of a wine. The most common attributes described in wines after MLF include buttery, caramel, smoky, sweaty, nutty, oaky and yeasty. strongly aromatic and floral varieties such as Riesling tend to cover the effects of MLF, whereas the occurrence of MLF in less aromatic wines such as Chardonnay is more easily discerned. Additionally, the organism used to
conduct MLF strongly influences the sensory changes that occur in a wine.

63

67.. You have a fermentation which has stopped.. List 5 analytical parameters that you should measure and justify why each is important for appropriate management and re - starting of the fermentation with a yeast rescue culture .

Addition of SO2 , addition of vitamins and supplements, addition of yeast hulls. Check temperature of ferment. Addition of DAP

64

68.. Write concisely on the formation of mousy off flavour in wine..

Dekkera has been implicated in the formation of other unpleasant off-flavour compounds such as an apple or cider-like aroma, ‘mousy-off-flavour’ (substituted tetrahydropyridine compounds) and phenolic taints

65

69.. Briefly discuss the causes,, impact upon wine composition and winemaking control of surface film growth..

Caused by genera Candida and Picha and manifests as small clumps of yeast . Yeast utilises ethanol to form acetic acid and acetaldehyde. Growth may be controlled by low temperature and high ethanol concentration, filling up storage space so no head space with wine, CO2 or Argon gas or filtration.

66

70.. Describe how the concurrent growth of yeast during fermentation may influence the population of lactic acid bacteria indigenous to the grape surface .

The most important factors affecting the growth of LAB may be summarised under wine composition, interactions with other microorganisms, and the influence of the winemaker.
A number of compositional factors influence the growth of LAB, including pH, the presence of ethanol, SO2, nutritional elements, and the oxygen tension of the wine.