1. Preparation of finished wines for bottling. Flashcards
Where is the wine put after blending?
Into the largest impervious inert vat possible.
Must be filled up completely or blanketed.
Mostly is stainless steel, sometimes concrete. Someone uses mild steel with epoxy linen.
Planning is essential so that empty vats are always present.
What is generally a big vat?
Depends on the winery: can go from 25hL (2500 liters) to 500hL (50000 liters) or more.
What is the best inert gas that can be used during pre bottling?
- Nitrogen - doesn’t dissolve in the wine, CO2 might get lost making wine dull.
- CO2 - heavier than air, but it soluble and gradually dissolves (especially in cold wines) letting air in.
The best option is a mix of CO2 and Nitrogen, the proportion is based on desired CO2.
What is constantly checked during this stage of pre bottling?
- Sulphur dioxide levels. Monthly to weekly. (It is constantly added to keep levels constant).
- Lowering dissolved oxygen.
- Adjustment of dissolved carbon dioxide.
- Slight acidification.
- Copper addition to avoid reduction.
How is sugar added at this stage and why?
- RCGM (concentrated grape must).
- Sussreserve (unfermented grape juice).
- Sucrose - banned in EU because there’s a high risk of starting a second fermentation.
Why?
- To make specific styles of “Medium Sweet Wine”.
- To soften the mouthfeel in red wines (smaller amount).
Is added here because wine becomes very susceptible to attack by microorganisms, especially yeast. A winemaker needs to avoid a second fermentation now.
What is checked in the lab analysis pre bottling?
- pH.
- Total Acidity.
- VA.
- Residual CO2.
- Dissolved oxygen.
- Turbidity.
- Filterability.
What are the requirements for traditional bottling (minimal technology)?
The only check necessary is to prevent piece of broken glass or flying insects to go into the bottle.
Enclosed bottling machine or bottling line is usually put in a separate room to avoid contaminations.
Principles of modern bottling.
Keep microorganisms low.
Main focus is to avoid yeasts, malolactic bacteria and acetobacter especially in the presence of high nutrients and malic acid in the wine.
Why it is called modern bottling?
Because other terms are misleading.
- Sterile bottling - sterile means absence of microorganisms, no attempt is made to eliminate them as alcohol and acidity do that naturally. No attempt is made to sterilise the bottle, only the bottling machine is.
- Aseptic bottling - prevention of putrefaction, it’s a good term but the only aseptic packaging is cardboard brick.
- Hygienic bottling - not all bottling is hygienic.
Why do you need bottling “aseptic” processes? What are they based on?
Used for unstable wines, usually with high sugar content, to eliminate yeasts.
Heat is the main principle.
- High temp - short time.
- Medium temp - medium time.
- Low temp - long time.
Bottling processes.
- Bottling line sterilisation.
- Bottle rinsing.
- Hot bottling.
- Tunnel pasteurisation.
- Flash pasteurisation.
- Cold sterile filtration.
- DMDC (dimethuldicarbonate).
How the bottle line is sterilised?
Flushes.
- Hot water (90C), cleans the bottle and kills microorganisms at the same time.
- Steam - less effective as lacks cleansing power of hot water and might bake the residues.
Chemical.
- Paracetic acid - non toxic hydrogen perixide and acetic acid combined, can also be left in the equipment for further sterilisation.
- Chlorine - not much used as it could form TCA.
Why bottles are not re-used much?
Cleaning and sterilised them is not practical and costs are high.
Many bottles might be contaminated with paraffin or petrol.
Options for bottle rinsing?
- No rinsing - bottles bought new are packed while hot so they are ready for filling.
- Machine with fresh and filtered water with SO2.
- Machine with filtered wine (to avoid water residue).
- Gas - blown into an upside bottle that removes foreign matter- is hygienic and has no water cost. Can also use nitrogen to reduce oxidation.
Main problem of bottle rinsing.
The operation can easily result in a less clean bottle unless the machinery is in immaculate conditions.
How hot bottling works?
- Wine passes through a heat exchanger at 54C.
- Bottled at 54C.
- Slowly cool to ambient temperature in controlled temperature storage.
Low level of heat + long cooling time.
Advantages and disadvantages of hot bottling.
Advantages.
- Complete sterilisation.
- Advances maturity of easy drinking reds.
Disadvantages.
- Heat can damage the wine.
- Needs low microbiological load - if high bacteria/yeast will not die.
- Filling might be problematic - when the wine will cool down level will be lower (also because of the movement of the cork - screwcap is the best option).
What is the main point of pasteurisation? What are the two main methods?
Heat can slow the deterioration of milk and wine.
Wine needs a lower temperature. Milk is between 80C and 90C, wine needs around 75C.
- Tunnel.
- Flash.
Why pasteurisation is common in Kosher wines?
Kosher wines are made, bottled, opened and poured by Jews.
As that is not always possible pasteurisation is done so that non-Jews can open it and pour it.
A Jew controller called “Mashgiach” needs to be present and bottle labeled as Mevushal, for Passover (also no corny syrup or flour cannot be used).
How tunnel pasteurisation works?
- Wine is bottled cold.
- Bottle is heated at 82C in a tunnel by hot water (15 min).
- Cold water.
The whole process is 45 minutes.
It is widely use - especially for sparkling (e.g. Asti).
Advantages and disadvantages of tunnel pasteurisation.
Advantages.
- Only good hygiene is required - no sterile techniques.
Disadvantages.
- Equipment and setup is expensive.
- High energy use.
- Heat can damage the wine - expert labour is required.
How flash pasteurisation works?
From the vat wine passes through a metal plate heat exchanger at 75C and then cooled down.
Widely used.
Main problems of flash pasteurisation.
- If the bottling machine is contaminated the wine will get reinfected.
- Requires specific labour - machine, filling, bottle preparations (clean and not older than a month), sterilised cork, etc.
Why cold sterile filtration is so widely used?
- Cheap.
- Reliable.
- Doesn’t need to heat up the wine.
It is called cold because the wine is not heated up, the wine is not chilled in this process.
How cold sterile filtration works?
Wine is filtered through sheet in a tight formation. At the end there’s a final membrane that captures eventually all the yeasts/microorganisms that escaped the process.
Two important choices for cold sterile filtration.
- Sheet grades - according to the body of the wine.
- Pore sizes of the final membrane - in red wines 1.2m to remove yeasts, in white/rose 0.65/0.45m to remove malo to block secondary ferment in bottle.
Main problem of cold sterile filtration.
If over-used can strip the wine off flavours and body.
The difference is felt nonetheless after every use. The wine needs to rest and then comparative tastings needs to be done.
Critical points of control during cold sterile filtration.
- Check that bottles and closures are sterilised.
- Training operators only.
- Sterilise filling machine and test for absence of yeasts and bacteria.
- Check of filters and membranes.
- Bottles needs to be filled and closed as fast as possible.
- A final tests needs to be done before sales to check presence of yeasts and bacteria in order to avoid rebottling after sales (much more cost).
How DMDC (dimethyldicarbonate) works?
- Colourless liquid (DMDC) is added to the wine - 200mg/L maximum.
- In contact with wine it hydrolise by water into methanol (low safe levels) and carbon dioxide.
- Inactivates the enzymes in the microorganisms and kills them.
