WINE MICRO PART 2 Flashcards
(66 cards)
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.. What media is used to select and differentiate acetic acid bacteria from wine.. Abbreviations are unacceptable..
Glucose Yeast Extract Carbonate Agar (GYC)
3.. Name two genera of acetic acid bacteria of relevance to wine production..
Lactobacillus and Pediococcus or Oenococus
4.. What are the three major functions of malolactic fermentation in wine??
Deacidification;
Increased microbial stability
Modification of flavour and aroma.
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.. 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
What causes spoilage with Acidification?
Excessive amounts of acetic acid and D lactic acid by homofermentative and heterofermentive LAB
What causes bitterness in wines
Glycerol is metabolised to form acrolein which reacts with anthrocyanins to produce a bitterness taint know as amertume
What causes Buttery taint?
Excessive production of diacetyl 1-4mg ok above 4mg is considered off.
What causes geranium off flavour?
Transformation of sorbic acid to sorbinol which forms the geranium off odour
What causes Histamine production?
Formed through decarboxylation of amino acids e.g hystamine,tyramine
What causes Manitol taint?
Formed through reduction of fructose by heterofermentative LAB
What causes mousy off flavour?
Production of 2 - acetyletrahydropyridines by heterofermantative LAB
What causes Ropiness?
Due to the development of a viscous character as oily or slimy (also known as la graisse)
What cause Tartaric Acid fermentation?
Tartaric acid is metabolised by species Lactobacillus to produce in part acetic acid resulting in increased volatile acidity
- What are the 3 major end products of heterolactic acid fermentation??
CO2, lactic acid and ethanol/acetate
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
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.
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.
12.. Name 3 genera of lactic acid bacteria associated with wine production..
Pediococcus, Oenococcus, Lactobacillus
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.
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.
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)
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.