Unit 4 - Lesson 4 - Grape Flashcards
Difference in grape must fermentation and malt or others?
- High starting sugar concentration
- low pH value (<4 pH) stresses yeast
- Brix is higher from high sugars
- Ferment without climate control meaning cold winters slow fermentation
- Maybe nutrient deficient due to laws no adding
- With nat fermentation low yeast count to start
Problem with high Brix?
Potential increased osmotic pressure on yeast
Could lead to more esters
What are typically the only items checked for grape must?
Brix and pH
Maybe for visible bacteria or yeast in a lab
Why is yeast assimilable nitrogen (YAN) important
Health of the yeast
What happens if YAN is too high or too low
Can create hydrogen sulphides
What is typical if winemakers do not check YAN?
Adding 100-300 mg/L of nitrogen
What is the problem with just adding DAP (di-ammonium phosphate). DAP is an inexpensive, inorganic nitrogen source?
It doesnt provide other nutrients
What are some other nutrients that may be added?
Yeast hulls Sterols and fatty acids Free amino acids Folic acid Zinc Magnesium
What yeast is typically chosen for brandy?
- Select a commercial strain suitable for wine or spirits production.
- Allow the yeasts naturally present in the juice or on thegrapesto proceed with fermentation.
What are commercial yeast strains for wine, what form?
Dry
Only need it once a year
It is simple, economical and consistent
Torulaspora delbrueckii
yeast species produces pleasant aromatic profiles in wine. It also reduces acetic acid and acetaldehyde levels in wine
Metschnikowia
Wine yeast not capable of fermenting high amounts of sugar, but do produce an array of fruity aromas
Brettanomyces
A widely studied genus of yeasts, prized by some winemakers, and feared by others. They produce volatile phenols that may contribute smoky, medicinal, and barnyard aromas which are considered off-flavours to some winemakers in various parts of the world.
Saccharomycescerevisiae
Common in vineyards around the world
These yeasts are usually the primary consumers of juice sugars, and thus produce the bulk of the wine’s alcoho
Why use natural yeast for brandy?
- Complex flavor
- Cheaper than commercial
- Law may ban eg Calvados
- Marketing - Artisan/Craft
How does natural yeast fermentation profile look?
- Crush juice is immediately available for natural yeast
- non Saccharomyces starts fermentation
- Saccharomyces grows and takes over
- 24-48 hr Saccharomyces is usually dominate
Why would a natural wine maker use cold maceration?
To let other yeast flourish before Saccharomyces takes over
What is the hybrid approach some yeast companies are doing for natural wine?
Isolating those beneficial natural yeasts other than Saccharomyces
Cultivating while keeping unwanted out
Style of fermenters in wine?
Cylindro conical like beer
What are key points of wine fermenters?
- Solid construction
- Easy to clean
- Taller than wide 2:1
4, Option to have cooling ability
What is MLF?
It is not a alcohol fermentation
Malic acid is turned to lactic acid
Malic is tart / Lactic soft creamy
Also creates Diacetyl
When does MLF occur?
After fermentation
Kloeckera apiculata
A species of yeast naturally present ongrapesfrom all over the world. It is usually not very competitive with other yeasts, and can be kept at bay by them. However, given the opportunity, this yeast can produce large amounts of ethyl acetate.
Acetobacter
A genus of bacteria that forms films on top of wine that has been exposed to the air for too long. These bacteria metabolise ethanol to produce acetic acid and ethyl acetate. The result is often a vinegar-like aroma in the wine.
