13. General Winemaking Options Flashcards
What is the maximum temp. desired for fermentation?
Why (2)?
35 C / 95 F is max.
Above this, fermentation slows down / stops as yeasts struggle to survive. This can lead to stuck fermentation.
What are benefits of concrete fermentation vessels (3)?
- high thermal inertia (maintain an even temperature more efficiently than steel)
- natural lees stirring occurs in egg-shaped vessels through convection currents.
- after initial investment, cost is low (re-usable)
At what concentration must a wine state that it “contains sulfites?”
>10mg / L of SO2
Explain what happens to SO2 when it is added to must/wine (3):
In what forms does SO2 exist when added to wine and which form is most effective?
When added to must/wine, SO2 dissolves and some of it reacts w/compounds in the liquid
=> Dissolved portion is called ‘bound SO2’ and is ineffective against oxidation/microbial spoilage
=> The unbound portion is ‘free SO2’.
Vast majority of free SO2 exists in a relatively inactive form, and a small portion is in the active molecular form, which is the most effective form.
How does the timing and size of SO2 additions influence its efficacy (4)?
- Adding a larger amount at 3 key points is more effective than small amounts throughout:
CRUSHING / END OF MLF / BOTTLING
What are disadvantages of cultured yeast? (2)
1) can lead to a similarity of fruit expression (“industrial wine”)
2) adds the cost of using a commercial product
What happens if Nitrogen levels in must are low during fermentation?
What can winemakers do to correct this?
- Low nitrogen levels can lead to stuck fermentations and rotten egg smells from sulfur compounds.
- Winemakers can add yeast nutrients, e.g. Diammonium phosphate / thiamine.
What does the fermentation process also produce aside from alcohol, CO2 and heat (4)?
1) volatile acidity (not enough to be detected)
2) very small amounts of naturally produced SO2
3) wine aromatics (from aroma pre-cursors + those created by yeast)
4) glycerol (increases body of wine)
What are benefits of stainless steel fermentation vessels (5)?
- easy to clean
- large range of sizes available
- high level of mechanization (temp. control, auto pump-over, auto-emptying)
- neutral vessels (no added flavors from oak/oxygen)
- after initial investment, cost is low (can be re-used indefinitely)
Historically, how did MLF occur?
How can it occur now (2)?
- often happened spontaneously in spring as temps rose.
- now process can be started by adding cultured lactic acid bacteria + ensuring favorable conditions.
How does the presence of oxygen influence growth of spoilage bacteria?
Favors the growth of spoilage bacteria e.g. acetic acid bacteria + Brett., esp if other conditions are favorable, e.g. presence of RS.
Why would / wouldn’t a wine maker conduct malolactic conversion in barrels vs larger batches in tanks (2)?
- Allows for the ability to stir lees at the same time as malo and promote better integration of flavors.
- This is also more labor-intensive because barrels may be at different temps, so all barrels need to be monitored individually.
How can controlled exposure to oxygen be good for some wines (6)?
- promotes growth of yeast population to start/maintain fermentation.
- lessens reductive off-flavors.
- can lead to greater oxygen stabalization in some white wines = increased aging potential.
- essential for reaction btw/anthocyanins + tannins to create greater color stability in red wines.
- can give greater diversity of aromas/flavors (fresh vs dried fruits, honey, caramel, coffee etc…)
- vital for certain wines, e.g. Oloroso Sherry, Madeira, Tawny Port.
How will sorting differ for good/bad vintages and grapes intended for inexpensive/premium wines (4)?
- Good years: grapes might be in perfect condition, little sorting may be needed (MOG still needs to be removed)
- Bad years: greater level of sorting required to remove moldy / under-ripe grapes.
- Inexpensive wines: may not be sorted at all ($$$+time for machinery/labor)
- Premium wines: only the highest quality grapes will be used, high level of sorting required.
What are 3 options for removal of alcohol after fermentation?
1) adding water (dilutes flavour)
2) reverse osmosis (most common high-tech option, very $$$)
3) spinning cone (extracts vol. aroma compounds from wine then removes alcohol – flavour components added back in)
What is the difference between crushing and pressing?
- crushing = breaking grape’s skins and releasing juice, making it available for fermentation
- pressing = separation of juice/wine from skin/seeds
What is the French word for grape sorting?
Triage
Besides stainless steel, concrete and wood, what are 2 fermentation vessels used by wineries?
1) Plastic vessels (useful for small-batch, but permeable to oxygen + hard to control temp.)
2) Terracotta (e.g. amphorae in Georgia)
What are the 2 pictures below of?
1) Pneumatic Press
2) Basket Press
What is the relationship btw/Oxygen and Yeast (3)?
- Initially, yeasts need O to multiply quickly.
- Once O is used up by yeast via aerobic respiration, they switch to fermentation.
- Fermentation required the absence of oxygen (anaerobic environment).
What are some ways a winemaker can actively discourage MLF (5)?
- cooling temp to below 15 C / 59 F
- adding SO2
- adding lysozyme (kills lactic acid bacteria)
- move any batch that is undergoing MLF (prevents spread of LA bacteria)
- filter out LA bacteria.
What is reductive/protective winemaking?
Practice of minimizing oxygen exposure during winemaking process
What are (3) advantages and (2) disadvantages of wood fermentation vessels?
AD: - retains heat well
- allows a small amount of oxygen
- can be re-used (inexpensive in the long term)
DIS: - great care must be taken to maintain hygenic conditions (wood can harbor spoilage orgs.)
- Initial investment of new barrels is high.
What are the 2 main methods of chilling down grapes once they reach the winery?
What is a disadvantage of having to chill grapes, and how can this be avoided?
- Refrigeration unit (used for whole bunches); takes longer but can be a useful place to store grapes.
- Heat exchanger; works quickly on grapes that are de-stemmed/partially crushed.
Both methods = investments of equipment + energy usage. Harvesting at night/morning helps to avoid these costs.
What are disadvantages of ambient yeast? (3)
1) fermentation may start slowly – results in build-up of VA and spoilage yeasts (e.g. Brettanomyces) = off-flavors.
2) fermentation to dryness may take longer + higher risk of stuck fermentation.
3) consistent product can’t be guaranteed.
What is the most common species of yeast used in winemaking?
Why (4)?
- saccharomyces cerevisiae
- it can withstand high acidity/alcohol
- it is resistant to SO2
- reliably ferments must to dryness.
- there are different strains = winemakers can choose for desired outcome.
What are the 2 types of wine aromatics produced as a result of fermentation?
Give examples (2 each):
- Aromas from pre-cursors; e.g. thiols (gooseberry in SB), terpenes (floral notes in Muscat.)
- Aromas created by yeast; e.g. esters (banana from carbonic), acetaldehyde (paint thinner in Fino Sherry)
Why is de-acidification done?
What is the most common method and what is an alternative?
Why is the alternative less common?
- done in cool climates where grapes may have to be picked before they’re ripe (e.g. inclement bad weather)
- adding calcium carbonate (chalk) or potassium carbonate.
- Ion exchange is an alternative = much more expensive.
What are some things that can be done to minimize the threats of oxidation and acetic acid bacteria in transportation to the winery (4)?
1) harvesting at night (cooler temps)
2) addition of SO2 (anti-oxidant / anti-microbial)
3) putting grapes in cold storage once received at winery
4) sanitizing equipment/bins
In the EU, what are the max. concentrations of SO2 for red and white wines?
Red: 160 mg/L
White 210 mg/L
What is ambient yeast?
AKA (2)?
What are 2 species of ambient yeast?
Yeast that is present in the vineyard/winery
AKA “wild yeasts” / “natural yeasts”
Kloeckera / Candida
How do yeasts usually behave during a “wild fermentation” (3)?
- These yeasts will start the fermentation if not inoculated.
- Most die once alcohol > 5%
- Saccharomyces cerevisiae will soon become dominant yeast.
Why doesn’t destemming have to be carried out for machine-harvested grapes?
Machine-harvested grapes are collected by shaking grapes off their stems in the vineyard.
What is malolactic conversion?
When does it happen and why would a winemaker choose one time vs another?
- result of lactic acid bacteria converting malic acid into lactic acid and CO2 (and heat)
- happens after alcoholic fermentation and during it occasionally.
Studies have shown that when ML happens during fermentation it can increase fruity characteristics and reduce production times which saves money as the wines can be finished and sold earlier.
What is an example of a yeast cultured yeast species besides Saccharomyces cerevisiae and what particular wines is it used for?
Saccharomyces bayanus
Used for must w/high potential alcohol or for re-fermenting sparkling wine.
What is alcoholic fermentation?
The conversion of sugar into ethanol and CO2 carried out by yeast in the absence of oxygen (anaerobically)