Hydrogen sulfide: Difference between revisions

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Specifically, sulfide is an essential metabolic intermediate in the biosynthesis of cysteine and methionine, which are necessary for protein synthesis and cellular metabolism.<ref name="Moreira">Moreira, N., et al. [https://repositorio.ucp.pt/bitstream/10400.14/6812/4/Volatile%20sulphur%20compounds.pdf "Volatile sulphur compounds in wine related to yeast metabolism and nitrogen composition of grape musts."] ''Anal. Chim. Acta'' 2002. 458:157-167.</ref><ref name="Jiranek">Jiranek, V., et al. [https://aem.asm.org/content/aem/61/2/461.full.pdf "Regulation of Hydrogen Sulfide Liberation in Wine-Producing Saccharomyces cerevisiae Strains by Assimilable Nitrogen."] ''Applied and Environmental Microbiology.'' Vol. 61, No. 2. Feb. 1995. pp. 461–467.</ref><ref name="Huang"/> Sulfide is also now recognized as having important functions in detoxification, population signalling, and extending life span in yeast.<ref name="Huang">Huang, CW., et al. [https://academic.oup.com/femsyr/article/17/6/fox058/4056150 "Hydrogen sulfide and its roles in Saccharomyces cerevisiae in a winemaking context."] ''FEMS Yeast Research.'' Volume 17, Issue 6, September 2017</ref>
Specifically, sulfide is an essential metabolic intermediate in the biosynthesis of cysteine and methionine, which are necessary for protein synthesis and cellular metabolism.<ref name="Moreira">Moreira, N., et al. [https://repositorio.ucp.pt/bitstream/10400.14/6812/4/Volatile%20sulphur%20compounds.pdf "Volatile sulphur compounds in wine related to yeast metabolism and nitrogen composition of grape musts."] ''Anal. Chim. Acta'' 2002. 458:157-167.</ref><ref name="Jiranek">Jiranek, V., et al. [https://aem.asm.org/content/aem/61/2/461.full.pdf "Regulation of Hydrogen Sulfide Liberation in Wine-Producing Saccharomyces cerevisiae Strains by Assimilable Nitrogen."] ''Applied and Environmental Microbiology.'' Vol. 61, No. 2. Feb. 1995. pp. 461–467.</ref><ref name="Huang"/> Sulfide is also now recognized as having important functions in detoxification, population signalling, and extending life span in yeast.<ref name="Huang">Huang, CW., et al. [https://academic.oup.com/femsyr/article/17/6/fox058/4056150 "Hydrogen sulfide and its roles in Saccharomyces cerevisiae in a winemaking context."] ''FEMS Yeast Research.'' Volume 17, Issue 6, September 2017</ref>


Sulfide is produced mainly by molecular reduction of [[sulfate]] or [[sulfite]] present in the juice or wort.<ref name="Giudici">Giudici, P. and Kunkee, R.E. [https://www.ajevonline.org/content/45/1/107.short "The effect of nitrogen deficiency and sulfur-containing amino acids on the reduction of sulfate to hydrogen sulfide by wine yeasts."] ''Am. J. Enol. Vitic.'' 1994. 45:107-12.</ref><ref name="Moreira"/><ref name="Jiranek"/><ref name="Hallinan">Hallinan, CP, et al. [https://www.researchgate.net/profile/Vladimir_Jiranek/publication/229784618_Differential_utilisation_of_sulfur_compounds_for_H2S_liberation_by_nitrogen_starved_yeasts/links/5ae31890a6fdcc9139a11277/Differential-utilisation-of-sulfur-compounds-for-H2S-liberation-by-nitrogen-starved-yeasts.pdf "Differential utilisation of sulfur compounds for H<sub>2</sub>S liberation by nitrogen-starved wine yeasts."] ''Australian Journal of Grape and Wine Research''1999. 5, pp. 82-90.</ref><ref name="Huang"/><ref name="Osborne">Osborne, James. [http://blogs.oregonstate.edu/owri/2013/12/10/development-sulfur-odors-post-fermentation/ "Development of sulfur off-odors post-fermentation."] Oregon Wine Research Institute. 2013.</ref><ref name="Butzke">Butzke, CE and Park, SK. [https://pdfs.semanticscholar.org/5ee8/503db38eb8e0b117b62e499c21218eb0ffd7.pdf "Impact of Fermentation Rate Changes on Potential Hydrogen Sulfide Concentrations in Wine."] ''J. Microbiol. Biotechnol.'' 2011. 21(5). pp. 519–524</ref> Sulfate is fairly ubiquitous, and sulfite is a common addition in wine and sometimes in beer. Sulfide is also formed from elemental sulfur, which is sometimes used as an antifungal treatment on grapes<ref name="Huang"/><ref name="Moreira"/><ref name="Jiranek"/> Utilization of these sulfur-containing compounds to produce amino acids occurs through a series of steps called the Sulfate Reduction Sequence (SRS).
Sulfide is produced mainly by molecular reduction of [[sulfate]] or [[sulfite]] present in the juice or wort.<ref name="Giudici">Giudici, P. and Kunkee, R.E. [https://www.ajevonline.org/content/45/1/107.short "The effect of nitrogen deficiency and sulfur-containing amino acids on the reduction of sulfate to hydrogen sulfide by wine yeasts."] ''Am. J. Enol. Vitic.'' 1994. 45:107-12.</ref><ref name="Moreira"/><ref name="Jiranek"/><ref name="Hallinan">Hallinan, CP, et al. [https://www.researchgate.net/profile/Vladimir_Jiranek/publication/229784618_Differential_utilisation_of_sulfur_compounds_for_H2S_liberation_by_nitrogen_starved_yeasts/links/5ae31890a6fdcc9139a11277/Differential-utilisation-of-sulfur-compounds-for-H2S-liberation-by-nitrogen-starved-yeasts.pdf "Differential utilisation of sulfur compounds for H<sub>2</sub>S liberation by nitrogen-starved wine yeasts."] ''Australian Journal of Grape and Wine Research''1999. 5, pp. 82-90.</ref><ref name="Huang"/><ref name="Osborne">Osborne, James. [http://blogs.oregonstate.edu/owri/2013/12/10/development-sulfur-odors-post-fermentation/ "Development of sulfur off-odors post-fermentation."] Oregon Wine Research Institute. 2013.</ref><ref name="Butzke">Butzke, CE and Park, SK. [https://pdfs.semanticscholar.org/5ee8/503db38eb8e0b117b62e499c21218eb0ffd7.pdf "Impact of Fermentation Rate Changes on Potential Hydrogen Sulfide Concentrations in Wine."] ''J. Microbiol. Biotechnol.'' 2011. 21(5). pp. 519–524</ref> Sulfate is fairly ubiquitous, and sulfite is a common addition in wine and sometimes in beer. Sulfide is also formed from elemental sulfur, which is sometimes used as an antifungal treatment on grapes.<ref name="Huang"/><ref name="Moreira"/><ref name="Jiranek"/> Utilization of these sulfur-containing compounds to produce amino acids occurs through a series of steps called the Sulfate Reduction Sequence (SRS).


Bacteria can also produce sulfide.<ref name="Jiranek2002">Jiranek, V. [https://www.infowine.com/intranet/libretti/libretto7316-01-1.pdf "Causes of Hydrogen Sulfide Formation in Winemaking."] ''vinidea.net - Wine Internet Technical Journal.'' 2002. vol 3.</ref>
Bacteria can also produce sulfide.<ref name="Jiranek2002">Jiranek, V. [https://www.infowine.com/intranet/libretti/libretto7316-01-1.pdf "Causes of Hydrogen Sulfide Formation in Winemaking."] ''vinidea.net - Wine Internet Technical Journal.'' 2002. vol 3.</ref>

Revision as of 17:36, 20 March 2020

Hydrogen sulfide (H2S), or just "sulfide" is a microbe-derived off flavor. It is the most common of a group of fermentation products known as volatile sulfur compounds (VSCs). Sulfide aroma and flavor is often described as sulfurous like rotten eggs, "rhino farts", burnt match, or volcanic gas. It is also sometimes called a "reduced" or "reductive" aroma because it is more likely to accumulate under low-oxygen conditions.[1]

Sulfide is one of the most common off flavors that presents in wine and cider. It can also occur in beer and other fermented beverages.[2] In fact, a slight note of sulfide may be acceptable in some styles of lager (beer). The aroma/flavor threshold of H2S is within 0.0005-1.5 mg/L,[3][4][5][6][7][8][9][10]

Sulfide is a precursor to other VSCs, notably mercaptans and disulfides. Mercaptan sensory threshold in wine is 0.00002-0.002 mg/L.[4] In 2000, the “Guinness Book of World Records” lists ethanethiol (another VSC) as the “smelliest substance in existence” (at 0.0028 mg/L).[4] However not all VSCs are bad; some sulfur compounds are desirable and important for wine character.[11] Hydropolysulfides such as H2S2 and H2S3 have been shown to contribute to the flint and mineral odor in wine.[12]

Hydrogen sulfide is toxic is large amounts, however the odor threshold is well below the threshold for toxicity and therefore toxicity is not a concern.[13]

Sulfide should not be confused with sulfite or sulfate.

Sulfide Formation

Yeast produce sulfide naturally, as part of the production of certain amino acids.

Specifically, sulfide is an essential metabolic intermediate in the biosynthesis of cysteine and methionine, which are necessary for protein synthesis and cellular metabolism.[14][15][12] Sulfide is also now recognized as having important functions in detoxification, population signalling, and extending life span in yeast.[12]

Sulfide is produced mainly by molecular reduction of sulfate or sulfite present in the juice or wort.[16][14][15][17][12][18][5] Sulfate is fairly ubiquitous, and sulfite is a common addition in wine and sometimes in beer. Sulfide is also formed from elemental sulfur, which is sometimes used as an antifungal treatment on grapes.[12][14][15] Utilization of these sulfur-containing compounds to produce amino acids occurs through a series of steps called the Sulfate Reduction Sequence (SRS).

Bacteria can also produce sulfide.[19]

Causes of Overproduction

Yeast strain is one of the main factors influencing the production of sulfide.[5][17][20][21] Some strains of yeast are biologically much more prone to over-producing sulfide.

Lack of adequate yeast nutrients is another main factor.[4][5][15][18][22][23] In order for the yeast to scavenge the sulfide and incorporate it into cysteine and methionine, the yeast need plenty of nitrogen and co-factors such as pantothenic acid to form the precursors for these sulfur-containing amino acids.[5][15][24][25][26] If there is not enough of the precursor, the yeast release the hydrogen sulfide into the wine or beer. Any factors that increase nutrient demand (such as under-pitching) may also lead to increased sulfide production.

Elemental sulfur is frequently sprayed in the vineyard to fight grapevine powdery mildew, and the residual sulfur on grape has been observed to contribute to the formation of sulfide during fermentation by yeast, and the reappearance of VSCs after bottling.[12][14][15][1]

Timing of its Appearance

Maximum amounts of sulfide is liberated when the depletion of nitrogen occurs during the exponential growth phase. Conversely, when depletion of nitrogen occurs during the stationary phase, sulfide liberation is a lower amount and is short-lived.[15]

While sulfide formation occurs mainly during primary fermentation, additional VSCs can be formed at later stages. Their formation can be difficult to predict and is not necessarily related to sulfide issues during the primary fermentation.[18] The VSCs involved include mercaptans and disulfides that have distinctive aromas such as skunky, rubbery, garlic, onion, or cabbage-like.[18][12][27] These compounds often result from degradation of sulfur-containing compounds in the yeast lees or from the re-release of chemically-bound sulfide during aging or storage (even after packaging).[18][22][1] Sulfide can be formed when naturally bottle carbonating.[28]

"When conditions in the wine become more reductive (during barrel aging or in the bottle) the disulfides can be reduced back to mercaptans resulting in a reappearance of sulfide aromas.[29][30]

There is not always correlation between total sulfide produced by yeast during fermentation and the sulfide concentration in the final wine.[20][31]

Prevention

An ounce of prevention is worth a pound of cure. For best results, a multi-factorial approach is needed to reduce the sulfide level in the final wine.[18]

  • Farmers using a sulfur spray should limit residual sulfur on fruit to 7 mg/kg or less (with less than 1 mg/kg being ideal). Stop spraying at least 5 weeks pre-harvest for the lowest risk of sulfide formation.[1]
  • Low sulfide-producing and/or low nitrogen-requirement yeast strains may be considered.[19] Scott Labs and Renaissance Yeast have bred some wine yeast strains specifically to reduce sulfide production.[32][33]
  • Reduced sulfite usage has been shown to reduce liberation of sulfide.[17][15][19] Beer brewers using sulfite should adequately aerate/oxygenate to neutralize the residual sulfite when pitching (see low oxygen brewing).
  • Aeration is especially important in affecting nitrogen utilization, fermentation vigor, and hence sulfide stripping from the medium.[15][19]
  • Vitamins should be supplemented (except in beer, which generally contains adequate vitamins[citation needed]). Deficiencies of vitamins that act as co-factors to SRS enzymes (pantothenic acid and pyridoxine) cause overproduction of sulfide even when adequate nitrogen is present.[15][19][24][25][26] (See Yeast Nutrition for how to provide vitamins.)
  • Nitrogen supplementation can help lower sulfide production, but only when there are also adequate co-factors present for the SRS.[15][34] Otherwise nitrogen supplementation may increase sulfide production.[26][24][35][5][31][20] There may also be some variability among yeast strains or species with regard to whether increasing nitrogen decreases sulfide formation.[20][36] However, wort generally contains enough nitrogen, so nitrogen supplementation in beer may not be helpful (with the possible exception of kveik).[citation needed] (See Yeast Nutrition for how to provide nitrogen.)
  • Pitch healthy yeast at a good pitch rate to decrease nutrient demand.[citation needed] "Shocking" the yeast (rapid changes in growth conditions like temperature or pH) should be avoided.[19] (See yeast fermentation for proper yeast management.)
  • Generally lower temperatures decrease sulfide liberation, although not necessarily because of decreased production.[26] However each strain has an optimum fermentation temperature to minimize its production, so lower temperature doesn't always mean lower sulfide production.[21]
  • A shorter fermentation decreases the amount sulfide present at the end.[34] This is probably because fermentation time is linked to aeration and nutrient supplementation. (See yeast fermentation)
  • The exact role of lees on sulfide formation has not been established. Aging on lees could be the cause of the problem but also the solution; evidence of both the release of VSCs from lees and the removal of VSCs by wine lees has been widely reported. The conditions under which each phenomenon occurs is a very complex matter closely related with the yeast strain and the winemaking conditions.[37][18][38][39][40][41][42][43][3]

Removal

While large amounts of sulfide may be produced during fermentation, much of this sulfide is usually volatilized (off-gassed) from the wine or beer along with CO2 during active fermentation.[18][3] Any residual sulfide should be removed promptly because it becomes more difficult to remove the longer it stays in the wine.[44]

There are several approaches to removing excess sulfide post-fermentation:

  • Increased yeast contact after fermentation may remove sulfide and other VSCs faster.[3] However, this may not always hold true. See the prevention section above for more info.
  • Sulfide is highly volatile, and can be readily removed through sparging with inert gas (such as nitrogen or possibly carbon dioxide), although this approach will be less effective against other VSCs and it will strip desirable aromatic compounds.[1]
  • Sulfide is easily oxidized, so aeration (i.e. through racking) may be used.[1][4][18] Although some texts claim that aeration should be avoided because of the danger of forming other VSCs, such as disulfides, there is little data to support this concern in recent scientific literature, and low level of oxygen has actually been shown to reduce these compounds.[1][45] However, excessive oxidation can cause a loss of desirable sulfur compounds, such as the fruity "grapefruit, passionfruit" compounds critical to Sauvignon Blanc and many other fruity white wines.[1] Intentional aeration is generally not a good option for beer, however simply aging the beer may provide enough oxygen exposure to remove the sulfide.
  • Adding sulfite frequently eliminates sulfide.[4] Aeration combined with sulfite often gives adequate results in wine without need to resort to adding metals.[4][44]
  • Copper additions are a common practice for the removal of sulfide, since the binding of copper with thiols will cause them to precipitate.[18] However, these complexes are challenging to remove from wine, and they can potentially release the sulfide later.[12][46][47][48] In addition, copper might catalyze the release of sulfide from sulfur containing amino acids like cysteine, although this is still speculative.[1] A bench trial is needed to determine the optimal level of copper needed. The wine should be racked several days after adding copper.[18][44] Copper sulfate reacts with hydrogen sulfide and any other thiols or mercaptans in the wine. Therefore, if you are dealing with a wine variety rich in aromatic varietal thiols (e.g., Sauvignon Blanc), the addition of copper sulfate can actually reduce the wine’s varietal aroma in addition to treating the reduced aroma.[49] Disulfides are not removed by copper and the offensive aroma may reappear later if they are reduced back to mercaptans.[18][4] Copper does work in beer as well.[50]

Using Copper

Copper should not be added until the fermentation is complete and the amount of yeast material is reduced by racking. This is because yeast cells can bind with copper and reduce effectiveness, and because addition of copper during fermentation may promote sulfide production by yeast.[18]

Perform a quick test to determine whether copper will help remove the offensive aroma.
Perform a bench trial to determine the optimal (minimum required) level of copper to add.

A simple method of removing sulfide is to add enough 1 percent copper sulfate solution to produce about 0.1 ppm of copper in the wine. Then the wine should be stirred thoroughly, and after a few hours, the wine should be carefully smelled. Table 1 can be used to determine how much of the 1 percent copper sulfate solution is needed for a 0.1 ppm treatment. One treatment is often enough, but a second or even a third treatment may be necessary for difficult cases. The wine should be left undisturbed for several days after this treatment so the copper sulfide (a very fine black powder) can settle to the bottom of the container. Then the wine should be carefully racked off the copper sulfide residue.[44]

Concentrations of between 0.05 and 0.3 mg/L of copper are commonly added.[18]

Bench trial procedure

Excess copper sulfate can be removed with bentonite, yeast hulls, or fresh lees additions.[51] Contrary to conventional wisdom, the majority of added copper remains in wine and is not readily removed by racking or filtration.[1][46]

Copper(II)-citrate (Cu2C6H6O7) is recommended instead of copper sulfate since it is an "organic chelating agent" of copper meaning the copper does not totally go into the ionic form.[4] Consequently, it does not leave as much residual copper in the wine.[4] The manufacturer claims only about 50% goes into wine.[4]

  • copper sulfate: 1g = 0.255mg copper[4]
  • copper citrate: 1g = 0.350mg copper[4]
  • kupzit: 50g = 1g copper citrate = .350g copper[4]


Recent work has shown that dilution with brine can release metal-sulfide complexes such as copper sulfides (FrancoLuesma et al., 2014), and that this release is correlated with release during accelerated or normal aging. Interestingly, this release can also be triggered by ascorbic acid (Chen et al. 2016) – in other words, the commonly used “ascorbic acid test” may not be detecting disulfides as is commonly assumed, but instead may be detecting copper sulfide (or copper mercaptide) complexes![1]

Science

This whole section is under construction.

See https://aem.asm.org/content/aem/61/2/461.full.pdf for the pathway of H2S formation. (fig 1)[15], or https://sfamjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2672.2003.01827.x for the full pathway including protein synthesis and other byproducts.[24] or here: https://academic.oup.com/femsyr/article/17/6/fox058/4056150 for an in-depth review of the biological pathways.[12]

To be utilized for production of H2S, SO2 simply diffuses into the cell, equilibrates at cytosolic pH as bisulfite (HSO3-) and sulfite (SO32-), and thereby can actually accumulate to 60-times its extracellular concentration.[17][15]

Glutathione is naturally present in grape juice (∼1.3 to 102 mg/L) and can also be synthesized by yeast through the Sulfate Assimilation Pathway. The addition of glutathione to grape juice has been observed to increase H2S production.[12] The mechanism is not yet fully understood but it is generally assumed that glutathione is first hydrolyzed to cysteine, which is then degraded by cysteine desulfhydrase to release H2S under nitrogen-limited conditions (Rauhut 2009).[12]

H2S has been demonstrated to react with (E)-2-hexenal in grape juice to form the fruity varietal thiols 3-mercapto-hexanol and 3-mercaptohexylacetate.[12] However, only tiny amounts of thiols (<1%) are produced through this pathway as (E)-2-hexenal is rapidly metabolised by yeast during fermentation (Schneider et al.2006; Subileau et al.2008; Harsch et al.2013).[12]

Final wine concentration of glutathione was correlated with both total N and organic nitrogen.[34] (see http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.913.1799&rep=rep1&type=pdf)

Mercaptan: if H2S is not removed from the wine, it will react with ethanol or acetaldehyde to form a new, even nastier compound called ethyl mercaptan or ethanethiol (burnt rubber, garlic, mercaptan or ethanethiol (burnt rubber, garlic, cabbage).[4]
CH3-CH2OH + H2S → CH3-CH2-SH + H2O

Diethyl disulfide: if ethyl mercaptan is not eliminated, then two molecules of mercaptan can react to form another molecule, even more nasty
CH3CH2-SH + HS-CH2-CH3 → CH3-CH2-S-S-CH2-CH3 B.P. = +154°C (very non-volatile)

  • This molecule is impossible to eliminate from wine by normal means and has a very cheese-like aroma[4]

Reaction of sulfide with oxygen:[4] 2 H2S + O2 → 2 S + 2 H2O

Reaction of sulfide with sulfite:[4] 2 H2S + SO2•H2O → 3 S + 3 H2O

Reaction of sulfide with copper sulfate:[4] H2S + CuSO4 → CuS + H2SO4 Not quite sure about this.

Recent work suggests that copper complexes may serve as a latent source of free hydrogen sulfide (H2S) and other malodorous volatile thiols during wine storage.[1] Advanced methods for measuring this sulfide exist. (see https://www.ajevonline.org/content/68/1/91)

Amino Acids

Cysteine is commonly referenced as contributing to increased formation for sulfide, but in practice its effect is negligible since cysteine concentration in must is typically very low.[18][16][14][12][15] It is likely cysteine is being enzymatically catabolized to ammonium, pyruvate, and H2S directly (2, 46).[15] Indeed it is -- aspartate aminotransferase deaminates cysteine to give mercaptopyruvate, which in a subsequent step catalyzed by MST liberates H2S and pyruvate.[52] However, other in vivo studies suggested that deletion of yeast CYS4 or CSY3 did not reduce the production of H2S.[12] Grape juice usually contains plenty of sulfate (∼160 to 700 mg/L) but very low concentrations of cysteine and methionine (<20 mg/L).[12][19] Although cysteine-hydrolyzing enzymes which release H2S have been described (2, 46), cysteine is not important to excessive H2S production during winemaking because of its scarcity in grape juice (3, 18).[15][12] while a link between nitrogen depletion and H2S liberation continues to be reported (17, 27, 28, 40, 47), the direct involvement of cysteine has not been demonstrated.[15]

Adding cysteine increases sulfide and inhibits sulfite formation. Added methionine inhibits both sulfide and sulfite formation.[16] Conflicting research: The addition of 20 mg l−1 methionine to grape musts has no great effect on the production of hydrogen sulphide.[14] At low methionine concentrations, DAP impact on H2S is minimal, and at low ammonium concentrations the effect of methionine addition is likewise minimal.[23] Irrespective of the availability of an average nitrogen source, insufficient regulatory methionine derivatives are formed. The result is not only a derepression of the SRS (5–7), and thus increased H2S formation, but also a reduced incorporation of H2S into methionine[15] Methionine repressed the cysteine-induced increase in the H2S production but had no effect on the formation of SO2.[53]

The most potent amino acid suppressants of H2S liberation are typically those which support high growth rates, i.e., serine, glutamine, ammonium, aspartate, arginine, and asparagine, or amino acids which act as direct precursors for O-acetylserine or O-acetylhomoserine synthesis, i.e., serine and aspartate.[15]

Linear regression of published data (Fig. 1 and 2) showed a general negative correlation between juice arginine concentrations and total H2S formation as well as residual H2S concentration in wine.[5]

See Also

  • Randy Mosher has a good article about all the various VSCs in beer.

Additional sources not yet included


tox

amino acids in apple juice https://onlinelibrary.wiley.com/doi/full/10.1002/jib.519


AA


References

  1. ↑ a b c d e f g h i j k l Jastrzembski, J., and Sacks, G. "Sulfur Residues and Post-bottling Formation of Hydrogen Sulfide." Research News from Cornell’s Viticulture and Enology Program Research Focus 2016-3a.
  2. ↑ Smith, B. "Sulfur and Rotten Egg Aromas in Beer – Off Flavors in Home Brewing." BeerSmith™ Home Brewing Blog. 2018.
  3. ↑ a b c d Oka K, et al."Decrease in Hydrogen Sulfide Content during the Final Stage of Beer Fermentation Due to Involvement of Yeast and Not Carbon Dioxide Gas Purging." Journal of Bioscience and Bioengineering. Vol. 106, No. 3, 253–257. 2008.
  4. ↑ a b c d e f g h i j k l m n o p q r s t u Kaiser, K. "Controlling Reductive Wine Aromas." Brock University CCOVI lecture series. 1 Feb 2010.
  5. ↑ a b c d e f g Butzke, CE and Park, SK. "Impact of Fermentation Rate Changes on Potential Hydrogen Sulfide Concentrations in Wine." J. Microbiol. Biotechnol. 2011. 21(5). pp. 519–524
  6. ↑ "Hydrogen Sulfide, Hazards." Occupational Safety and Health Administration (OSHA). Accessed March 2020.
  7. ↑ "Hydrogen Sulfide1 Acute Exposure Guideline Levels." Acute Exposure Guideline Levels for Selected Airborne Chemicals. Volume 9. National Research Council (US) Committee on Acute Exposure Guideline Levels. Washington (DC): National Academies Press (US); 2010.
  8. ↑ "ToxGuide™ for Hydrogen Sulfide H2S" Agency for Toxic Substances and Disease Registry (ATSDR). December 2016.
  9. ↑ Odor perception and physiological response. The Science of Smell Part 1. Iowa State University. May 2004.
  10. ↑ "hydrogen sulphide." aroxa. Accessed March 2020.
  11. ↑ Swiegers, JH and Pretorius, IS. "Modulation of volatile sulfur compounds by wine yeast." Applied Microbiology and Biotechnology vol 74, 2007. pp.954-960.
  12. ↑ a b c d e f g h i j k l m n o p q Huang, CW., et al. "Hydrogen sulfide and its roles in Saccharomyces cerevisiae in a winemaking context." FEMS Yeast Research. Volume 17, Issue 6, September 2017
  13. ↑ Guidotti, TL. "Hydrogen Sulfide: Advances in Understanding Human Toxicity." International Journal of Toxicology. 2010. 29(6) pp. 569-581.
  14. ↑ a b c d e f Moreira, N., et al. "Volatile sulphur compounds in wine related to yeast metabolism and nitrogen composition of grape musts." Anal. Chim. Acta 2002. 458:157-167.
  15. ↑ a b c d e f g h i j k l m n o p q r s Jiranek, V., et al. "Regulation of Hydrogen Sulfide Liberation in Wine-Producing Saccharomyces cerevisiae Strains by Assimilable Nitrogen." Applied and Environmental Microbiology. Vol. 61, No. 2. Feb. 1995. pp. 461–467.
  16. ↑ a b c Giudici, P. and Kunkee, R.E. "The effect of nitrogen deficiency and sulfur-containing amino acids on the reduction of sulfate to hydrogen sulfide by wine yeasts." Am. J. Enol. Vitic. 1994. 45:107-12.
  17. ↑ a b c d Hallinan, CP, et al. "Differential utilisation of sulfur compounds for H2S liberation by nitrogen-starved wine yeasts." Australian Journal of Grape and Wine Research1999. 5, pp. 82-90.
  18. ↑ a b c d e f g h i j k l m n o Osborne, James. "Development of sulfur off-odors post-fermentation." Oregon Wine Research Institute. 2013.
  19. ↑ a b c d e f g Jiranek, V. "Causes of Hydrogen Sulfide Formation in Winemaking." vinidea.net - Wine Internet Technical Journal. 2002. vol 3.
  20. ↑ a b c d Ugliano, Maurizio, et al. "Effect of Nitrogen Supplementation and Saccharomyces Species on Hydrogen Sulfide and Other Volatile Sulfur Compounds in Shiraz Fermentation and Wine." J. Agric. Food Chem. 2009, 57, 11, 4948-4955.
  21. ↑ a b Kim YR, et al. "Effects of Yeast Strains and Fermentation Temperatures in Production of Hydrogen Sulfide During Beer Fermentation." Korean J. Food Sci. Technol. 2008. Vol. 40, No. 2, pp. 238-242.
  22. ↑ a b Rauhut, D. "Yeasts – production of sulfur compounds" in Wine Microbiology and Biotechnology. ed. G.H Fleet. Harwood Academic Publishers, Switzerland. 1993. p. 183-223.
  23. ↑ a b Spiropoulos, A., et al. "Characterization of Hydrogen Sulfide Formation in Commercial and Natural Wine Isolates of Saccharomyces." Am. J. Enol. Vitic. 2000. 51:233-248.
  24. ↑ a b c d Wang, XD, et al. "Fermentative activity and production of volatile compounds by Saccharomyces grown in synthetic grape juice media deficient in assimilable nitrogen and/or pantothenic acid." Journal of Applied Microbiology. 2003. 94, pp. 349-359.
  25. ↑ a b Tokuyama, Takashi, et al. "Hydrogen Sulfide Evolution Due to Pantothenic Acid Deficiency in the Yeast Requiring this Vitamin, with Special Reference to the Effect of Adenosine Triphosphate on Yeast Cysteine Desulfhydrase." J. Gen. Appl. Microbiol. 19, 1973. pp. 439-466
  26. ↑ a b c d Bohlscheid, Jeffri C, et al. "Interactive Effects of Selected Nutrients and Fermentation Temperature on H2S Production by Wine Strains of Saccharomyces." Journal of Food Quality. 2011. 34 pp. 51-55.
  27. ↑ "Volatile Sulfides: Detection and Prevention." ETS Laboratories. Accessed online March 2020.
  28. ↑ "Preventing sulfide when bottle conditioning." homebrewtalk.com. 2019.
  29. ↑ Ferreira, Vicente, et al. "Elusive Chemistry of Hydrogen Sulfide and Mercaptans in Wine." J. Agric. Food Chem. 2018, 66, 10, pp. 2237-2246.
  30. ↑ Vela, Eduardo, et al. "Micro-oxygenation does not eliminate hydrogen sulfide and mercaptans from wine; it simply shifts redox and complex-related equilibria to reversible oxidized species and complexed forms." Food Chemistry. Volume 243, 15 March 2018. pp. 222-230.
  31. ↑ a b Ugliano, Maurizio, et al. "Occurrence of hydrogen sulfide in wine and in fermentation: influence of yeast strain and supplementation of yeast available nitrogen." Journal of Industrial Microbiology & Biotechnology. volume 38. 2011. pp. 423-429.
  32. ↑ "Understanding the Production of Hydrogen Sulfide (H2S) During Fermentation." Scott Laboratories. scottlabs.com Accessed March 2020.
  33. ↑ "10 g Fresco Cider Yeast - H2S Preventing." The Beverage People. Product page. Accessed March 2020.
  34. ↑ a b c Park, SK, et al. "Formation of Hydrogen Sulfide and Glutathione During Fermentation of White Grape Musts." Am J Enol Vitic. January 2000 51: 91-97.
  35. ↑ Kumar, GR, et al. "Survey of Hydrogen Sulfide Production in Wine Strains of Saccharomyces cerevisiae." Am J Enol Vitic. September 2010 61: 365-371.
  36. ↑ Mendes-Ferreira, A., et al. "Survey of Hydrogen Sulphide Production by Wine Yeasts." Journal of food protection. 65(6):1033-7. 2002.
  37. ↑ Pérez-Serradilla, JA and Luque de Castro MD. "Role of lees in wine production: A review." Food Chemistry. Volume 111, Issue 2, 15 November 2008, pp. 447-456.
  38. ↑ Bautista, R., et al. "Effect of the contact with fermentation-lees or commercial-lees on the volatile composition of white wines." European Food Research and Technology 2007 volume 224, pp 405-413.
  39. ↑ Tamayo C, et al. "Relationship between H2S-producing strains of wine yeast and different fermentation conditions." Canadian Journal of Microbiology. 1999, Vol. 45, No. 4. pp. 343-346.
  40. ↑ Palacios, S., et al. "Evidence For Sulfur Volatile Products Adsorption by Yeast Lees." Am J Enol Vitic. January 1997 48: 525-526/
  41. ↑ Vasserot, Y., et al. "Study of thiol consumption by yeast lees." Antonie van Leeuwenhoek 83: 201–207, 2003.
  42. ↑ Bueno, JE, et al. "Effect of a Short Contact Time With Lees on Volatile Composition of Airen and Macabeo Wines." Biotechnology Letters. volume 28, pp. 1007-1011. 2006.
  43. ↑ Kraft, DN. "Impact of Lees Content, Nitrogen, and Elemental Sulfur on Volatile Sulfur Compound Formation in Vitis vinifera L. cv. ‘Pinot noir’ wine." Master's Thesis, 2015.
  44. ↑ a b c d "Removing H2S (Hydrogen Sulfide)." The Vintner's Vault. Accessed online March 2020.
  45. ↑ McCord, Jeff. "Application of toasted oak and micro-oxygenation to ageing of cabernet sauvignon wines." 2003.
  46. ↑ a b Clark, AC, et al. "Copper(II) addition to white wines containing hydrogen sulfide: residual copper concentration and activity." Australian Journal of Grape and Wine Research. 2015. 21: 30-39.
  47. ↑ Ugliano, Maurizio, et al. "Evolution of 3-Mercaptohexanol, Hydrogen Sulfide, and Methyl Mercaptan during Bottle Storage of Sauvignon blanc Wines. Effect of Glutathione, Copper, Oxygen Exposure, and Closure-Derived Oxygen." J. Agric. Food Chem. 2011, 59, 6, 2564-2572
  48. ↑ Viviers, MZ., et al. "Effects of Five Metals on the Evolution of Hydrogen Sulfide, Methanethiol, and Dimethyl Sulfide during Anaerobic Storage of Chardonnay and Shiraz Wines." J. Agric. Food Chem. 2013. 61, 50, pp. 12385-12396.
  49. ↑ Gardner, D. "Wine Flaw Focus: Hydrogen Sulfide and “Reduction”." Denise Gardner Winemaking (dgwinemaking.com). October 19, 2018.
  50. ↑ Walker, MD. "The influence of metal ions on concentrations of flavour‐active sulphur compounds measured in beer using dynamic headspace sampling." J. Sci. Food Agric. 1995. 67:1 25-28.
  51. ↑ Gardner, D. "Sulfur-based Off-flavors in Wine." Pennsylvania State University. Feb 14, 2020
  52. ↑ Kabil, O. and Banerjee, R. "Redox Biochemistry of Hydrogen Sulfide." The Journal of Biological Chemistry. Vol. 285, No. 29, pp. 21903-21907. July 16, 2010.
  53. ↑ Duan, W. et al. "A Parallel Analysis of H2S and SO2 Formation by Brewing Yeast in Response to Sulfur-Containing Amino Acids and Ammonium Ions." Journal of the American Society of Brewing Chemists. 62:1, 35-41. 2004.
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