Ch 13 : General Winemaking Options Flashcards
What are the main risks in grape transportation to the winery?
Oxygen
Ambient yeasts
Acetic acid bacteria
What are protective and preventative options for grape transport?
Harvesting and transporting at night
Adding SO2 at harvest
Putting grapes in cold storage
Sanitising tools to avoid microbial spoilage
Collecting in small batches to minimise crushing
What are the two functions of SO2
Anti oxidative
Anti microbial
What techniques would a winemaker use to promote oxygen exposure in the wine?
Cap management
Small wooden vessels
Lee’s stirring and racking
Allowing ullage
Hyperoxidation
How would a winemaker protect their wine/must from oxygen?
Minimising ullage
Flushing vessels with inert gas
Adding SO2
Using innert vessels
Fermenting and storing at cool constant temperatures
When are SO2 additions most effective?
At crushing, Malo, and bottling. Ideally in larger amounts compared to constant smaller additions throughout
How does pH affect SO2 efficacy?
At lower pH, the environment favours the development of molecular SO2 which is most effective. A low pH wine may not require so much SO2 which is cheaper and may help winemakers adhere to laws and guidelines in their region/style (eg organic, AOP etc.)
What are the negative affects of oxygen in wine?
Acetaldehyde
Colour change
Biological instability eg. Brettanomyces, acetic acid
What are oxidation reactions?
When oxygen acts indirectly on the wine or must by promoting one reaction which develops reactive compounds that may affect colour, flavour etc.
What are the most common press types
Pneumatic press and basket press
What are the benefits of a pneumatic press?
Can be programmed for different pressures
Can be flushed with inert gas prior
Can be a big up front expense, seen more in mid to large scale winemaking
What are the benefits of a basket press
Exposure to oxygen for certain styles
More artisan in nature
When would a winemaker add rcgm/sugar to enrich the wine?
After ferment has started as yeast are active and can handle the high sugar levels
What options, aside from must enrichment, exist to concentrate grape sugars?
Reverse osmosis
Vacuum evaporation
Cyroextraction
How would a winemaker reduce alcohol levels?
Adding water to the must
Removing alcohol from wine post ferment
Why would a winemaker expose their white grape must to oxygen before fermentation?
greater long term oxygen stability
increased ageing potential
what are the two roles of SO2?
antimicrobial
antioxidant
What are the max levels of SO2 permitted for red and white wines in the EU
150 mg/L for reds
200 mg/L for whites
what are the three forms of SO2
bound
free
molecular
will the proportion of SO2 required be higher or lower at a pH of 3.1?
lower, because there is more molecular SO2 available
What are options for grape sorting?
- sorting at picking
- hand sorting
- optical sorting
difference between pressing and crushing
crushing releases the juice
pressing removes the juice from skins and seeds
what are the most common pressing options
pneumatic press
basket press
screw press
continuous press
what constituents can be added to must in enrichment?
dry sugar
grape must
grape concentrate
RCGM
What processes can result in must enrichment?
reverse osmosis
vacuum extraction
chilling
When is enrichment often carried out?
once ferment has started as yeasts are active
when is acidification carried out?
before ferment starts to benefit from effects of lower pH and enhance acid integration during ferment
What does yeast need to ferment?
viable temperature, nutrients, nitrogen, no oxygen
at what alcohol % do most yeasts species die out
5%
what are the risks of ambient ferment?
slow start means potential build up of VA and growth of spoilage organisms (eg. Brett)
Why does yeast need nitrogen?
its a nutrient. Without sufficient nitrogen, the yeast gets stressed and produces undesirable sulphur compounds or stops ferment
what are common yeast nutrient additions?
Diammonium phosphate (DAP)
thiamine (B1)
what are the ferment temperatures for cool, mid, and warm brackets?
cool : 12-16C
mid : 17-25C
warm : 26-32C
what are the required conditions for MLF?
18-22C
moderate pH (3.3-3.5)
low total SO2
how can winemakers artificially ensure MLF does not occur?
adding the enzyme lysozyme
dropping temperatures
adding SO2
how does MLF affect the wine?
less acid, raised pH
colour loss in red wine
microbial stability
flavour modification
name two alcohol removal techniques
reverse osmosis
spinning cone
how does reverse osmosis work?
- cross-flow filtration removes flavourless permeates of water and alcohol
- this is then distilled to remove the alcohol
- the watery permeate is blended back into the wine
