Off-flavors Flashcards
Ethyl acetate
- nail polish, solvent, glue
- Biggest influence is air, increased production under aerobic conditions
- Aroma threshold 7.5 mg/L
Higher alcohols (fusel alcohols) (4)
- Increased time in contact with solids increases higher alcohols red wines tend to have higher alcohols.
- Extremely important for the production of esters
- Origin in Amino acids
- Concentration depends on amount of amino acids that you start with as well as ethanol, fermentation temp, pH, must composition, amount of solids, skin contact time
Volatile Acids
- Volatile fatty acids
- Acetic Acid
Important note about Acetic Acid (2)
- Small increase with MLF
- There are two Pathways
1. Produced from res. sugar through heterolactic metabolism
2. First step in citric acid metabolism
Carbonyl compounds
Acetaldehyde
*Increase over time due to oxidation of EtOH - due to
aeration
* Use of high conc of SO2 can cause accumulation of acetaldehyde
* Precise control of sulphur dioxide to provide protection it can completely block acetaldehyde
when aware of slight oxidation we can increase sulphur dioxide
Diacetyl
- Carbonyl compound
- Significant production during MLF by lactic acid bacteria
◦ < 1-4 mg/L nutty or toasty
◦ > 1-4 mg/L buttery or butterscotch
◦ > 5 mg/L undesirable – rancid butter - Biggest influence is air, increase production under aerobic conditions
Volatile Phenols
- Mostly are from Brettanomyces
- They can be produced during fermentation from
Saccharomyces cerevisiae - Spoilage organisms in barrel and cellar
- Band-aid, medicinal, pharmaceutical, barnyard-like, horsey, sweaty, leathery, mouse urine, wet dog, smoky, spicy, cheesy, rancid, metallic
Sulfur compounds
*Sulfides, polysulfides, heterocyclic compounds.
*Produced by yeast
–Degradation of sulfur-containing amino acids
–Degradation of sulfur-containing pesticides
–Release and/or metabolism of grape-derived sulfur-containing precursors
Sulfides
- Hydrogen sulfide (H2S) – rotten egg
- Symptom of yeast suffering due to lack of nutrients
- Degradation of yeast, we can add oxygen and we need to
supply nutrients
Hydrogen Sulfide (HS2)
When comparing red and white wine
and temp of ferm
in white wine with have a bigger risk for
h2s because the alc ferm temp
is lower. The yeast is slightly stressed
and H2S is more common with sparkling wine as well
because of the CO2 in secondary ferm.
H2S is the waste of the yeast when stressed
Thiols
◦ Low aroma thresholds > 1.1 μg/L
◦ Ethanethiol (onion, rubber, natural gas)
◦ Methanethiol (cooked cabbage, onion, putrefaction (rot), rubber)
◦ Their presence during fermentation suggest that they are by-product of yeast metabolism
Light Struck Defect
*methanethiol and ethanethiol
*Mercaptans such as ethanethiol can be formed by reaction of H2S with ethanol or acetaldehyde
* Yeast can reduce disulfides to thiols such as ethane- and methanethiol
Mousy (How many compounds)
*3 known compounds causes mousy aroma (ETPY, ACTPY, ACPY)
* Oxygen, high redox potential, high pH, Iron are positive environment for mousy off-flavor production
Mousy (What causes what)
Brett causes 2
Lactic Acid Bacteria causes 3
Cork Taint
Due to Penicillium, Aspergillus, Streptomyces naturally present
* on cork
* in cork industries
* in cellar environment
they develop at low umidity and metabolize phenolics of cork
