Agriculture Reference
In-Depth Information
• MLF also contributes to increased flavour complexity.
In white wines where the fruit aromas are the most important aspect of the desired
style, MLF can be inhibited by initially chilling the wine and maintaining a free SO
2
level of approximately 20-30 ppm to achieve a molecular SO
2
level of 0.5-0.8 ppm.
Storage and Maturation of Wine
The main types of storage vessel are stainless steel tanks or a variety of different
sized oak barrels. Oak barrels are used to import oak characters through lactones.
Different oak characters may be delivered with the use of different toasting levels,
sizes and types (eg French or American) of barrels. Stainless steel tanks are inert
and help minimise oxidation to maintain the wine's fruit aromas. They also allow
the following steps to be performed as necessary;
• Potassium bitartrate stability
• Protein stability.
• Other fining including the use of protein fining agents and copper sulphate.
These steps are outlined in “Wine Chemistry” (see below).
Bottling When the wine is ready for bottling it is fine-filtered, generally sterile
grade using pads and/or membrane filters, and immediately filled into bottles or
bag in box containers. A number of different types of fillers are in use for different
applications. The most basic form is a simple syphon filler while more sophisticated
machines fill under vacuum or under an overpressure of inert gas. Important aspects
in bottling are the prevention of oxidation and the prevention of microbiological
contamination by careful sterilisation of equipment and sterile filtration.
Wine Microbiology
The production of wine from grape juice or must is fundamentally a microbial
process. Grape juice and wine are largely inhibitory to the growth of most organ-
isms due to the low pH and high osmotic pressures in juice and must, and high
concentrations of ethanol in finished wine. Arising from these selective pressures,
it is only highly adapted organisms that are capable of growth in grape juice, must
or wine. Numerous microorganisms participate in the production process and may
contribute in a positive or negative manner to the overall sensorial qualities of the
end product. The impact of microorganisms upon the wine making process is sum-
marised in Table
7.5
. Unquestionably the most important microbial process in wine
production is the bioconversion by yeast of fermentable carbohydrates glucose and
fructose into ethanol. Yeast growth and metabolism also contribute significantly to
the overall sensory properties of the wine. Yeasts are responsible for the conver-
sion of certain aroma precursors to volatile compounds; metabolism of organic
