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==History of Scientific Research==
[[File:THP microbes.jpg|thumb|200px|right|Grbin et al. (1996) Survey of microorganisms that produce THP <ref name="Grbin_1996" />.]]
THP in wine ("mouse taint") was first described in wine by Müller-Thurgau and Osterwalder in 1913, although mention of an off-flavor in wine that 'is closely resembling the smell of a residence of mice' dates to 1894 in "A Treatise on wines" by J.L.W. Thudichum. Müller-Thurgau and Osterwalder attributed it to be produced by bacteria. They also established that the ability to detect THP varies from person to person <ref name="Grbin_1996" />. A 1908 text by the Germans Nessler and Windish linked THP off-flavors to wine that aged longer on lees, perhaps due to yeast autolysis <ref name="Snowdon" />. In the 1940's, some scientists proposed that THP was purely a chemical reaction, however, their evidence was inconclusive. In 1977, Tucknott et al. was able to identify that THP production was attributed to both ''Brettanomyces'' yeast and lactic acid bacteria, and that ethanol and L-lysine played a role in its production, and this was confirmed by Heresztyn et al. in 1986 <ref name="Grbin_1996">[httphttps://iwrdbdigital.sonomalibrary.org/cgi-bindigital/collection/p15763coll33/id/koha34976/opac-detail.pl?biblionumber=27016&shelfbrowse_itemnumber=19456 rec/1 Developments in the sensory, chemical and microbiological basis of mousy taint in wine. Grbin, P.R, Costello, P.J, Herderich, M. 1996.]</ref>.
The chemical analysis of THP has proven to be a difficult endeavor in science. In 1995, Herderich et al. out of Australia developed a method for chemically analyzing THP for the first time. It was at this time that all three forms of THP (ETHP, ATHP, and APY) could be identified consistently in contaminated wine. It was also during this time that the three forms of THP contributed to the flavor of various foods, such as tortilla chips and taco shells. For example, APY was found in the fermentation of cocoa in 1995. In 1995, Grbin et al. described ''Brettanomyces'' yeast as the yeast that produces THP, while wine strains of ''S. cerevisiae'' did not <ref name="Grbin_1996" />.
In 2000, the Australians Grbin and Henschke showed that some strains but not all of ''B. bruxellensis'', ''B. anomalus'', ''B. nardenensis'', and ''B custersianus'' produce THP, and that THP production was influenced by the carbon source, but not dependent on it (THP was still produced in dry wines with little available nutrients, and fermentation rate was not always related to THP levels) <ref name="Grbin_2000">[http://onlinelibrary.wiley.com/doi/10.1111/j.1755-0238.2000.tb00186.x/abstract PAUL R. GRBIN and PAUL A. HENSCHKE. 2000.]</ref>.
In 2007, the Australian team of Grbin et al. developed a complex and unique method of analyzing forms of THP using a Finnigan TSQ 70 mass spectrometer directly coupled to a Varian 3400 gas chromatograph. The chromatograph was equipped with a 30 m J&W Carbowax 20 CAM fused silica column, 0.25 mm i.d, and 0.25 μm film thickness. They were able to confirm confirmed that higher lysine levels increased the amount of ATHP produced (but not ETHP), although with diminishing increases of THP as the lysine level was increased. They also discovered that L-ornithine also functioned as a precursor for THP production in ''Brettanomyces''. The group proposed a biochemical pathway for the different forms of THP in ''Brettanomyces'' <ref name="Grbin_2007" />. More recently, Hayasaka (2018) developed a reliable and rapid but pricey method to detect THP in wine using specialized HPLC-APCI-MS/MS equipment <ref>[https://www.sciencedirect.com/science/article/pii/S0021967318315668?via%3Dihub Quantitative analysis of mousy off-flavour compound 2-acetyl tetrahydropyridine in wine using liquid chromatography tandem mass spectrometry interfaced with atmospheric chemical ionisation. Y.Hayasaka. 2018. DOI: https://doi.org/10.1016/j.chroma.2018.12.047.]</ref>.
==Detection Methods==In 2007, Grbin et al. developed a complex and unique method of analyzing forms of THP using a Finnigan TSQ 70 mass spectrometer directly coupled to a Varian 3400 gas chromatograph. The chromatograph was equipped with a 30 m J&W Carbowax 20 CAM fused silica column, 0.25 mm i.d, and 0.25 μm film thickness <ref name="Grbin_2007" />. More recently, Hayasaka (2018) developed a reliable and rapid but pricey method to detect THP in wine using specialized HPLC-APCI-MS/MS equipment <ref>[https://www.sciencedirect.com/science/article/pii/S0021967318315668?via%3Dihub Quantitative analysis of mousy off-flavour compound 2-acetyl tetrahydropyridine in wine using liquid chromatography tandem mass spectrometry interfaced with atmospheric chemical ionisation. Y.Hayasaka. 2018. DOI: https://doi.org/10.1016/j.chroma.2018.12.047.]</ref>. Due to the specialized GC/MS equipment needed for measuring forms of THP that most labs do not have, certain answers will be difficult other human sensory-based methods have been developed in the winemaking world. Originally, a "palm & sniff" method was developed to detect THP where a small amount of wine is rubbed on the palm which increases the pH of the wine and then immediately sniffed to obtaindetect THP. Some Since then, some studies have used alkaline strips as a way to smell the aroma of THP, and while not as precise as the specialized GC/MS lab equipment, could still help further the understanding of THP. These strips were prepared in the following way: knowing Knowing that mousy off-flavour flavor has a lingering sensory impact, the technique of alkaline paper strip assessment was adapted from Heresztyn (1986a). Paper strips (Whatman No. 1, 4–5 mm × 50 mm) were prepared by soaking in NaOH (0.1M) and drying overnight at room temperature. The alkaline paper strips were then briefly dipped into cell-free samples (centrifuged) and immediately assessed for the mouse-like odour odor by sniffing <ref>Private correspondence with Dr. Paul Grbin by Dan Pixley. 11/2/2017.</ref>. Tempère et al. (2019) developed what they suggest is a better way to test for mousy off-flavor in wine via oral sensory, specifically as a way to enable panelists who are not as sensitive to THP to detect it during sensory testing. They compared the alkaline strips method to a method where the wine's pH is increased by adding sodium bicarbonate to a pH of 5 and a pH of 7. This mild base is contained in human saliva. At a pH of 5, sensory panelists were more easily able to detect APY and to correctly order the intensity of APY in wine than when they used alkaline strips. For example, the range of detection level for all panelists went from a range of 15 - 300 µg/L to a range of 0.3 - 30 µg/L. At a pH of 7, panelists were not as easily able to detect the aroma of APY. Keep in mind that this test does not reflect the real world tasting of wine since the pH would never be raised during normal consumption, but it could be used by a sensory program as a way to more reliably detect smaller amounts of APY in wine <ref name="Tempère_2019">[https://oeno-one.eu/article/view/2350 Comparison between standardized sensory methods used to evaluate the mousy off-flavor in red wine. Tempère, S., Chatelet, B., de Revel, G., Dufoir, M., Denat, M., Ramonet, P.-Y., Marchand, S., Sadoudi, M., Richard, N., Lucas, P., Miot-Sertier, C., Claisse, O., Riquier, L., Perello, M.-C., & Ballestra, P. 2019. DOI: https://doi.org/10.20870/oeno-one.2019.53.2.2350.]</ref>. Kiyomichi et al. (2023) developed a simple method to accurately detect ATHP, ETHP, and APY using gas chromatography-mass spectrometry with stir bar sorptive extraction (SBSE-GC–MS instrumentation). Thermal desorption and injection were performed using a Twister thermal desorption unit (TDU) and a Gerstel CIS 4 cooled injection system with a programmable temperature vaporization (PTV) inlet, installed on an Agilent 6890 gas chromatograph combined with an Agilent 5975 Mass Selective Detector (Agilent Technologies, Massy, France), equipped with a Gerstel MPS 2 autosampler (Gerstel, Mülheim an der Ruhr, Germany). An HP-5MS fused-silica capillary column (30 m × 0.25 mm, 0.25 µm, film thickness, SGE, Courtaboeuf, France) was used, with helium as carrier gas (Messer France S.A.S, Suresnes, France) at a constant pressure of 70 kPa, corresponding to an initial flow of 1.3 mL.min−1 <ref>[https://www.sciencedirect.com/science/article/abs/pii/S0308814623000705 Daiki Kiyomichi, Céline Franc, Pierre Moulis, Laurent Riquier, Patricia Ballestra, Stéphanie Marchand, Sophie Tempère, Gilles de Revel. Investigation into mousy off-flavor in wine using gas chromatography-mass spectrometry with stir bar sorptive extraction. Food Chemistry, Volume 411, 2023, 135454, ISSN 0308-8146, https://doi.org/10.1016/j.foodchem.2023.135454.]</ref>. See also [https://ives-technicalreviews.eu/article/view/7867 "Simultaneous assay of mousy off-flavor markers in wine," Ives Technical Review]. Other techniques for detected THP in food have been developed, which might be applicable to wine or beer. For example, Grimm et al. (2001) developed a technique for detecting 2-acetyl pyrroline (APY or 2AP) in rice. The rice samples had to be heated to 80-85°C in order to extract the volatile APY, and then APY levels in the headspace of the rice container could be detected using solid phase microextraction (SPME) with fibers that operate at the higher temperatures <ref>[https://www.ncbi.nlm.nih.gov/pubmed/11170584 Screening for 2-acetyl-1-pyrroline in the headspace of rice using SPME/GC-MS. Grimm CC, Bergman C, Delgado JT, Bryant R. 2001.]</ref>. It isn't known if such methods would also work for measuring THP compounds in beer or wine, but they could provide a potential option for beer and wine researchers. Cider makers have used a baking soda in water solution to help detect THP. Dissolve a small amount of baking soda in water, swish the solution in your mouth for a few seconds, and then spit it out. While the pH of the saliva in your mouth is raised from the baking soda solution, taste the beer/wine/cider to more easily detect THP <ref>[https://groups.google.com/g/cider-workshop/c/a9JcCERQTYk?pli=1 "testing for mouse". Testing for Mouse. Retrieved 04/06/2021.]</ref>. The effectiveness of these methods in beer has not been reported to our knowledge (please report any research or anecdotes in the [https://www.facebook.com/groups/MilkTheFunk/ MTF Facebook group]).
==Forms of THP==
===ATHP===
===ETHP===
It has been speculated by scientists studying mousy off-flavors in wine that its production is the result of slow metabolism of ATHP into ETHP by ''Brettanomyces''. ETHP was observed to form much slower than ATHP, and coincided with a decrease in ATHP. This slow production of ETHP may be another reason it has been underestimated by researchers until recently <ref name="Snowdon"></ref>. It is not known whether or not ETHP has not been shown to break down can degrade into another byproduct.
===APY===
===Unidentified "Transient" Forms===
[[File:THP Pathway.JPG|thumb|400|Proposed pathway for THP production by ''Brettanomyces'' <ref name="Elsevier">[https://books.google.com/books?hl=en&lr=&id=KJJwAgAAQBAJ&oi=fnd&pg=PA346&dq=brettanomyces+Tetrahydropyridine&ots=ktbn8PR_fF&sig=r3lkcV-gBa-pK86HSOgFDVIJVDk#v=onepage&q=brettanomyces%20Tetrahydropyridine&f=false Managing Wine Quality: Oenology and Wine Quality. A Reynolds Elsevier, Sep 30, 2010. Pg 359.]</ref>]]
It is thought that THP in mousy wines/beers is mostly produced by microorganisms. All species of ''[[Brettanomyces]] '' can produce forms of tetrahydropyridine in varying amounts, although some below threshold. Additionally, Lactic Acid Bacteria (LAB) including ''[[Lactobacillus]] '' and ''[[Pediococcus]] '' can produce forms of THP. Acetic Acid Bactera (AAB) has also been demonstrated to produce forms of THP <ref name="Snowdon"></ref><ref name="Grbin_2000" />.
Moulis et al. (2023) studied THP production by 22 strains of ''Brettanomyces bruxellensis'', 20 strains of ''Oenococcus oeni'' and 10 strains of ''Lentilactobacillus hilgardii'' (formerly classified as ''Lactobacillus hilgardii''), all of which have been reported to produce THP compounds. They found that all strains could produce ATHP, but not all strains could produce ETHP or APY. This variability was determined mostly by species, but also by strain. for example, all of the 22 ''B. bruxellensis'' strains only produced ATHP and ETHP and not APY. Variability between strains was less pronounced for the species ''L. hilgardii'' compared to the ''B. bruxellensis'' and ''O. oeni'' strains (different strains of ''B. bruxellensis'', for example, produced much different levels of ATHP/ETHP, where as every strain of ''L. hilgardii'' produced relatively the same amount of APY). The researchers also noted that repeatability of THP levels was difficult to achieve, and they owed this to unknown variables such as the physiological state of the cells at time of inoculation into the test media. Interestingly, there was no correlation between strain genealogy and how much THP they produced. The researchers also isolated other species from 25 French wines with mouse taint, including ''S. cerevisiae'', ''Pichia manshurica'', ''Priceomyces carsonii'', ''Pediococcus parvulus'', but none of these strains produced THP in the test growth media <ref name="Moulis_2023" />. ===''Brettanomyces''===
Although the exact pathway is not known for ''Brettanomyces'' (several are proposed), the conditions for THP production are well documented. ATHP is produced by metabolizing the amino acid L-lysine or D-lysine <ref name="Grbin_2007" />, along with ethanol and a glucose or fructose molecule. Iron is also needed for THP production, although its exact role in biosynthesis is not known <ref name="Snowdon"></ref>. As with other amino acids, lysine is taken up by ''Saccharomyces'' during fermentation and then released after fermentation. Levels of lysine fluctuate slightly throughout fermentation but are generally high throughout a beer's lifetime (including after fermentation) <ref>[http://link.springer.com/article/10.1385/CBB:46:1:43 The α-aminoadipate pathway for lysine biosynthesis in fungi. Hengyu Xu, Babak Andi, Jinghua Qian, Ann H. West , Paul F. Cook. Sept 2006.]</ref><ref>[http://pubs.acs.org/doi/abs/10.1021/bi9829940 Lysine Biosynthesis in Saccharomyces cerevisiae: Mechanism of α-Aminoadipate Reductase (Lys2) Involves Posttranslational Phosphopantetheinylation by Lys5. David E. Ehmann , Amy M. Gehring , and Christopher T. Walsh. 1999.]</ref><ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2007.tb00249.x/abstract Elucidation of the Role of Nitrogenous Wort Components in Yeast Fermentation. C. Lekkas, G.G. Stewart, A.E. Hill, B. Taidi and J. Hodgson. May 2012.]</ref><ref>[http://www.sciencedirect.com/science/article/pii/S0308814699000710 Proteins and amino acids in beers, their contents and relationships with other analytical data. S. Gorinstein, M. Zemsera, F. Vargas-Albores, J-L. Ochoa, O. Paredes-Lopez, Ch. Scheler, J. Salnikow, O. Martin-Belloso, S. Trakhtenberg. 1999.]</ref>. Wheat generally has a slightly lower amount of lysine than barley, and oats have a slightly higher amount of lysine than barley <ref>[http://www.aaccnet.org/publications/cc/backissues/1983/Documents/chem60_461.pdf Amino Acid Composition of Six Grains and Winter Wheat Forage. Morey, D.D. 1983.]</ref><ref>[https://diy.soylent.com/ingredients/oats "Oats". DIY Soylent website. Retrieved 02/07/2017.]</ref><ref>[https://diy.soylent.com/ingredients/barley-malt-flour "Barley malt flour". DIY Soylent website. Retrieved 02/07/2017.]</ref><ref>[https://diy.soylent.com/ingredients/wheat-flour-wholegrain "Wheat flour, whole-grain". DIY Soylent website. Retrieved 02/07/2017.]</ref>. In red wine, yeast autolysis releases many amino acids including lysine <ref>[https://pubs.acs.org/doi/abs/10.1021/jf9803381 Changes in the Amino Acid Composition of the Different Nitrogenous Fractions during the Aging of Wine with Yeasts. Victoria Moreno-Arribas, Encarnación Pueyo, M. Carmen Polo, and Pedro J. Martín-Álvarez. 1998. DOI: 10.1021/jf9803381.]</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/12483471 Influence of the yeast strain on the changes of the amino acids, peptides and proteins during sparkling wine production by the traditional method. Martínez-Rodríguez AJ, Carrascosa AV, Martín-Alvarez PJ, Moreno-Arribas V, Polo MC. 2002. DOI: 10.1038/sj.jim.7000323.]</ref><ref>[http://oeno-one.eu/article/view/974 New trends on yeast autolysis and wine ageing on lees: a bibliographic review. Caroline Fornairon-Bonnefond, Carole Camarasa, Michel Moutounet, Jean-Michel Salmon. 2002.]</ref>. Aging beer on trub and its effects on THP production has not been studied, but it might not be a factor in beer since lysine levels are high in beer regardless of yeast autolysis <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2054994917862045/?comment_id=2055489394479264&reply_comment_id=2055715194456684&comment_tracking=%7B%22tn%22%3A%22R%22%7D Richard Preiss. Milk The Funk Facebook group thread on on yeast autolysis impact on THP. 04/10/2018.]</ref>.
The production of ATHP is not efficient, meaning that the amount of ATHP produced is not proportional to the amount of L-lysine consumed. Therefore, the production of ATHP appears to be a byproduct (secondary metabolite) of L-lysine catabolism <ref name="Snowdon"></ref>. ATHP is further metabolized into ETHP by ''Brettanomyces'', although not much is known about this metabolic process <ref>[http://ucce.ucdavis.edu/files/repositoryfiles/Joseph_5_Aromatic_Diverswity_of_Brettanomyces-82350.ppt Joseph, C.M. Lucy. ''Aromatic Diversity of Brettanomyces''. U.C. Davis. Retrieved 3/10/2015.]</ref><ref name="Snowdon"></ref>. ETHP has a significantly higher taste threshold, and is often not detected in contaminated wine <ref name="Oelofse"></ref>.
Although ''Brettanomyces'' is capable of producing APY from L-ornithine <ref name="Grbin_2007" />, the amount produced is much less than that of LAB and high amounts of L-ornithine are required. In wine, there isn't enough L-ornithine present to production significant amounts of APY from L-ornithine. Therefore, the presence of APY (which is much easier to detect aromatically than ATHP) indicates a bacterial contamination in wine (it is unknown if this applies to beer) <ref name="Snowdon"></ref>. Additionally, Moulis et al. (2023) found that out of 25 French wines with THP, only 20% of them had ''B. bruxellensis'' in them, indicating that THP is mostly produced by bacteria or chemically in wine <ref name="Moulis_2023" />.
The presence of the "mousy off-flavor" caused by forms of THP appears to be temporary in beer. Although not much is known about the degradation or metabolic breakdown of ATHP/ETHP, it tends to age out of beer after 2-6 months. Since the odor/taste threshold for ETHP is much higher than ATHP, and ATHP appears to be metabolized into ETHP by ''Brettanomyces'' over time, this may be one of the mechanisms by which the mousy off-flavor ages out of beer. The possibility of ETHP breakdown is not mentioned in any studies that we know of, although Moulis et al. (2023) reported that for organisms that produced ETHP, there was always a 1:10 ratio between ETHP/ATHP or ETHP/APY, suggesting that this ratio might be governed by the chemistry of the media used and/or the [https://en.wikipedia.org/wiki/Reduction_potential reduction potential] <ref name="Moulis_2023" />. Another unknown is why does ''Brettanomyces'' produce ATHP shortly after kegging and force carbonating a beer that has reached final gravity. The most likely cause is oxygen pick up during the kegging process. Pitching fresh ''Saccharomyces'' at bottling/kegging time and naturally carbonating the beer with sugar has reportedly reduced mousy off-flavor detection, perhaps because ''Saccharomyces'' metabolizes both the oxygen and sugar faster than ''Brettanomyces''.
===Lactic Acid Bacteria===
[[File:THP path bacteria.JPG|thumbnail|right|[http://pubs.acs.org/doi/abs/10.1021/jf020341r Proposed pathway of APY and ATHP by ''L. hilgardii'' by Costello and Henschke (2002).]]]
Heterofermentative [[Lactobacillus]] spp., particularly ''L. hilgardii'' (reclassified as ''Lentilactobacillus hilgardii'') and ''L. brevis''(reclassified as ''Levilactobacillus brevis''), as well as ''Leuconostoc oeni'' <ref name="Grbin_1996" />, can also produce high levels of ATHP , and to a lesser extent APY and ETHP from L-lysine/L-ornithine, ethanol (must be present), and iron. Although many strains of heterofermentative lactic acid bacteria can produce THP, not all do. For example, Costello et al (2008) found that all strains tested of ''L. brevis'' (3 strains tested), ''L. bucherni'' (3 strains tested), and ''L.hilgardii'' (8 strains tested) produced THP, several heterofermentative species did not produce any detectable levels of THP in a grape-based media (one strain each of ''L. fermentum'' and ''L. cellobiosus''). Some strains within a species produce high amounts while others produce low amounts, for example Costell et al. (2008) found that some strains of ''O. oeni'' produced very high amounts between 50-150 µg/L while others produced very little between 5-20 µg/L in a grape-based media <ref name="Costello_2008">[http://onlinelibrary.wiley.com/doi/10.1111/j.1755-0238.2001.tb00205.x/abstract Ability of lactic acid bacteria to produce N-heterocycles causing mousy off-flavour in wine. PETER J. COSTELLO1, TERRY H. LEE1, and PAULA. HENSCHKE. 2008.]</ref>. A strain of ''L. plantarum'' (L11a) was shown to produce relatively low amounts. L-lysine stimulates production of ATHP, and L-ornithine stimulates the production of APY <ref name="Costello">[http://pubs.acs.org/doi/abs/10.1021/jf020341r Mousy Off-Flavor of Wine: Precursors and Biosynthesis of the Causative N-Heterocycles 2-Ethyltetrahydropyridine, 2-Acetyltetrahydropyridine, and 2-Acetyl-1-pyrroline by Lactobacillus hilgardii DSM 20176. Peter J. Costello and Paul A. Henschke. 2002.]</ref><ref>[http://www.ajevonline.org/content/37/2/127.abstract Formation of Substituted Tetrahydropyridines by Species of Brettanomyces and Lactobacillus Isolated from Mousy Wines. Tamila Heresztyn. 1986.]</ref><ref name="Costello_2008" /><ref>Sparrows, Jeff. ''Wild Brews''. Brewers Publications. 2005. Pg. 112.</ref><ref>[https://books.google.com/books?id=tFjsAuo5WocC&pg=PA348&lpg=PA348&dq=lactobacillus+Tetrahydropyridine&source=bl&ots=QUVyoFtIwK&sig=h1cdjB0r1pIRX2Bms8wVA0UiLk4&hl=en&sa=X&ei=4DX_VPz5CsH6oQSAzoGgBA&ved=0CEwQ6AEwCQ#v=onepage&q=lactobacillus%20Tetrahydropyridine&f=false Lahtinen, Ouwehand, Salminen, von Wright. Lactic Acid Bacteria: Microbiological and Functional Aspects, Fourth Edition. Pg 348.]</ref><ref>[http://ajevonline.org/content/37/2/127.short Heresztyn, Tamila. Formation of Substituted Tetrahydropyridines by Species of Brettanomyces and Lactobacillus Isolated from Mousy Wines.]</ref>. Acetaldehyde has a stimulatory effect on ATHP and APY production, but is not required. No studies have been done to show whether or not oxygen plays a role in ATHP/APY production in LAB <ref name="Snowdon"></ref>. Most species of [[Pediococcus]] do not create forms of THP, although a few species do produce relatively small amounts. In particular, these include ''P. pentosaceus'' <ref>[http://www.uniprot.org/uniprot/Q03HT0 UniProt article. Retrieved 3/10/2015.]</ref><ref>[http://www.uniprot.org/uniprot/U5ZF76 UniProt article. Retrieved 3/10/2015.]</ref>, and ''P. clausenii'' <ref>[http://www.uniprot.org/uniprot/G8PEU4 UniProt article. Retrieved 3/10/2015.]</ref>, although one study found no THP in two strains of ''P. pentocaseus'' and only transient/occasional THP production in one out of five strains of ''P. parvulus'' <ref name="Costello" />. ''Oenococcus oeni'' and ''Leuconostoc mesenteroides'' have also been associated with creating ATHP, APY, and ETHP all above threshold amounts. Since only heterofermentative species produce significant amounts of THP, it is thought that its production is linked to the heterolactic pathway, and thus the metabolism of sugars in LAB <ref name="Costello"></ref>. A pathway for APY and ATHP production in ''Lactobacillus hilgardii'' was proposed by Costello and Henschke, which involves the intake of lysine or ornithine, along with ethanol (which is broken down into acetaldehyde) to produce APY and ATHP <ref name="Costello" />. ''Lactobacillus pontis'' has been shown to break down proteins via proteolysis, yielding free amino acids such as ornithine which could serve as precursors to THP formation, and it might be [[Lactobacillus#Foam_Degradation|reasonable to presume]] that other species of ''Lactobacillus'' could also free up ornithine as a precursor to THP <ref name="Adams_2005" />.
===Acetic Acid Bacteria and Mould===
Although research is limited, acetic acid bacteria (''Gluconobacter'' sp. and many strains of ''Acetobacter aceti'') have been shown to produce forms of THP <ref name="Snowdon"></ref>. Mediterranean dried sauses covered in [[Mold|mould]] have been characterized as having APY as a flavor contributor. The source of the APY was identified with a mould that grows on the surface called ''Peniciilium nalgiovense'' <ref name="Adams_2005" />. Moulis et al. (2023) identified several strains of acetic acid bacteria in 32% of selected French wines with mouse taint, but none of the strains produced THP when tested individually in model medium <ref name="Moulis_2023" />.
===Maillard Reactions===
===Oxygen Reactions===
(In Progress)
Grbin (1996) reported that some wines express mousy taint after oxidation <ref name="Grbin_1996" />, however, ATHP in food has been identified as being very volatile in the presence of oxygen <ref>[https://www.sciencedirect.com/science/article/pii/S1021949815000277?via%3Dihub Reactivity and stability of selected flavor compounds. Monthana Weerawatanakorn, Jia-Ching Wu, Min-Hsiung Pan, Chi-Tang Ho. 2015. DOI: https://doi.org/10.1016/j.jfda.2015.02.001.]</ref><ref name="Tempère_2019" />.
Shilpi Halemane from Logsdon Farmhouse Ales anecdotally reported getting THP in bottles that were not purged properly on their bottling line, and this was detected at the end of the day on the same day <ref>"Wild Beer Curling: Course Correcting and Guiding Your Beer to Success". HomebrewCon Seminar. 2018.</ref> (~14:50 mins in).
https://www.facebook.com/groups/MilkTheFunk/permalink/2053443891350481/?comment_id=2053628131332057&reply_comment_id=2054035171291353&comment_tracking=%7B%22tn%22%3A%22R9%22%7D
https://pubmed.ncbi.nlm.nih.gov/22508009/
===THP in Kettle Souring===
** Concentration reported in wines exhibiting mousy off-flavour: Trace quantities up to 7.8 µg/L <ref name="Snowdon"></ref><ref>[http://kb.osu.edu/dspace/bitstream/handle/1811/56335/OARDC_HCS_0744_ppt_18_Gerstenbriand.pdf?sequence=27 Malolactic Fermentation 2005. Geneva on the Lake. Feb 2005. Retrieved 3/10/2015.]</ref>
Since a low pH hinders the detection of THP, one detection used by wine makers winemakers is to rub some wine on one's palm and smelling for THP. A more reliable method is to dip an alkaline paper strip into the wine, and then smelling the strip to detect the aroma of THP <ref name="Grbin_1996" />.
==Off Flavor Kits==
# Does the release of lysine from yeast autolysis when aging on trub increase THP potential (some say it does in wine and cider <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1852891514739054/ Tariq Ahmed of Revel Cider. Milk The Funk Facebook thread on THP in wines/ciders aged on lees. 10/16/2017.]</ref>)?
# Are other species of yeast such as wild ''S. cerevisiae'' capable of producing THP <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2069944559700414/ Zach Taggart. Milk The Funk Facebook group thread on other yeast species producing THP. 04/24/2018.]</ref>?
# Do sulfites sulphites bind to THP molecules, rendering them unperceivable <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2069944559700414/?comment_id=2070023539692516&reply_comment_id=2074259392602264&comment_tracking=%7B%22tn%22%3A%22R%22%7D Otto Forsberg. Milk The Funk Post discussion on THP and sulfites. 04/27/2018.]</ref>?
<nowiki>*</nowiki> Due to the specialized GC/MS equipment needed for measuring forms of THP that most labs do not have, certain answers will be difficult to obtain. Some studies have used alkaline strips as a way to smell the aroma of THP, and while not as precise as the specialized GC/MS lab equipment, could still help further the understanding of THP. These strips were prepared in the following way: knowing that mousy off-flavour has a lingering sensory impact, the technique of alkaline paper strip assessment was adapted from Heresztyn (1986a). Paper strips (Whatman No. 1, 4–5 mm × 50 mm) were prepared by soaking in NaOH (0.1M) and drying overnight at room temperature. The alkaline paper strips were then briefly dipped into cell-free samples (centrifuged) and immediately assessed for the mouse-like odour by sniffing <ref>Private correspondence with Dr.
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1766965029998370/ Joe Idnoni from House Cat Brewing and Brian Ogden from Attaboy Beer report that Caseinate de Potassium (a fining agent used in wine-making) was used to significantly reduce THP off-flavors in a kettle sour beer.] Note that casein is a milk allergen, and might require declaration as a milk allergen (refer to your local government requirements) <ref>[https://www.fda.gov/Safety/Recalls/ucm456836.htm "UPDATED - Allergy Alert on Undeclared Milk in Nutrition Resource Services, Inc.'s Whey, Casein, and Colostrum Protein Products". FDA website. 08/03/2015. Retrieved 12/21/2017.]</ref>.
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1852891514739054/ Tariq Ahmed of Revel Cider discusses their protocol for reducing THP in spontaneously fermented ciders.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/2627026050658926/?comment_id=2628780327150165&comment_tracking=%7B%22tn%22%3A%22R%22%7D Chris Cates with thoughts on water profile (sulfate) increasing the perception of THP in sour beer.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1624811250880416/ MTF thread detailing experiences with certain strains and procedures (03/24/2017).]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1967129246648613/ Milk The Funk thread on THP flavor spikes and other sensory testing approaches.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/2015071285187742/ Milk The Funk thread on anecdotal experiences of THP forming in beer lines.]
* [https://www.facebook.com/groups/MilkTheFunk/posts/7626497387378409/ Milk The Funk thread reporting an anecdote by Henrik Ventzel that adding some DME and fresh Nottingham yeast to a sour with THP and cleared up THP after 2 months.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1034461653248715/ General Milk The Funk Thread on March 10, 2015.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1134644959897050/ General Milk The Funk Thread on Aug 25, 2015.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1149568535071359/ General Milk The Funk Thread on 09/17/2015.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/2934892606538934/ MTF thread on THP in natural wine, and increased awareness of THP in wine. as a result.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/4042481855779998/ MTF thread on removing THP from wine made with low or no sulphite.]
* [https://www.masterbrewerspodcast.com/237 MBAA Podcast 237: David Fuhrer on bottle conditioning using the German speise method (similar to krausening) reduces THP.]
* [http://www.homebrewtalk.com/f127/brett-strain-production-athp-449852/#post6752813 Homebrewtalk thread started by "ne0t0ky0".]
* [http://www.homebrewtalk.com/f127/cheerios-character-after-bottling-504468/ Homebrewtalk thread started by "loctones", comments by Michael Tonsmeire.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1149568535071359/?comment_id=1159597500735129&offset=0&total_comments=17&comment_tracking=%7B%22tn%22%3A%22R%22%7D Kyle Weniger from Joseph James Brewing Co noticed significantly improved THP reduction storing a split batch of beer at room temperature versus storing cold.]
* [http://www.stitcher.com/podcast/the-brewing-network/the-sour-hour/e/the-sour-hour-episode-8-37471621 Chad Yakobson on The Sour Hour, 3/11/2015 (around 50 minute mark) - indicates that he has been researching THP for 2 years, and is continuing this research. Little else is mentioned.]
==See Also==
===Additional Articles on MTF Wiki===
* ''[[Lactobacillus]]''
* [[Butyric Acid]]
* [[Isovaleric Acid]]
* [[Mixed Fermentation]]
===External Resources===
* [https://www.youtube.com/watch?v=U-7IDTlg23o THP overview presentation by Richard Preiss at Escarpment Laboratories.]
* [https://punchdrink.com/articles/natural-wine-flaw-mouse/ "The Wine Flaw of Our Times," by John McCarroll.]
==References==