Enhancement of beer flavor by a combination of pichia yeast and different hop varieties

Abstract

In the beer fermentation process, Pichia spp. yeast strains can be combined with normal beer yeast strains and with different hop varieties to produce synergistic effects, including the increased production in the fermentation product of esters, e.g., increased levels of isoamyl acetate, isobutyl acetate, ethyl propionate, ethyl valerate, ethyl butyrate, ethyl decanoate, and ethyl octanoate. Additionally, the Pichia spp. strain interacts differently with different hop varieties, such that the flavor profile of beer can be tuned by employing different combinations of Pichia spp. strains and hops.

1 . A method of brewing beer comprising the steps of
 a) providing a wort;   b) adding at least one hop variety to obtain a hopped wort;   c) fermenting the hopped wort with a first yeast strain, wherein the first yeast strain is a  Pichia  spp. yeast strain; and   d) fermenting the hopped wort with a second yeast strain to obtain a beer, wherein the second yeast strain belongs to the genera  Saccharomyces  or  Brettanomyces.      
     
     
         2 . The method according to  claim 1 , wherein each of step c) and step d) is carried out sequentially. 
     
     
         3 . The method according to  claim 2 , wherein the fermentation in step c) is allowed to proceed for at least 12 hours, such as at least 24 hours, such as at least 36 hours, such as at least 48 hours, such as at least 60 hours, such as at least 72 hours, prior to the onset of the fermentation in step d). 
     
     
         4 . The method according to  claim 1 , wherein step c) and step d) are carried out at the same time by co-inoculation of the first yeast strain of step c) and the second yeast strain of step d). 
     
     
         5 . The method according to  claim 1 , wherein step d) is allowed to proceed for at least 24 hours, such as at least 36 hours, such as at least 48 hours, such as at least 72 hours, such as at least 96 hours, such as at least 120 hours. 
     
     
         6 . The method according to  claim 1 , wherein the at least one hop variety is selected from the group consisting of Saaz, Nelson Sauvin, Cascade and Amarillo. 
     
     
         7 . The method according to  claim 1 , wherein the fermentation in step c) is carried out at between about 12° C. and 28° C. 
     
     
         8 . The method according to  claim 7 , wherein the fermentation in step c) is carried out at between about 20° C. and 22° C. 
     
     
         9 . The method according to  claim 1 , wherein the  Pichia  spp. Yeast strain is a  Pichia kluyveri  strain. 
     
     
         10 . The method according to  claim 10 , wherein the  Pichia Kluyveri  strain is selected from the group consisting of  Pichia kluyveri  PK-KR1 and  Pichia kluyveri  PK-KR2 as deposited on 24 Aug. 2006 at the National Measurement Institute, 541-65 Clarke Street, South Melbourne, Victoria 3205, Australia, by University of Auckland, School of Biological Sciences, Auckland 1142, New Zealand, under accession numbers V06/022711 and V06/022712, respectively, and mutants and variants thereof. 
     
     
         11 . The method according to  claim 1 , wherein the second yeast strain is selected from the group consisting of  Saccharomyces cerevisiae, Saccharomyces pastorianus  and  Brettanomyces bruxellensis.    
     
     
         12 . The method according to  claim 1 , wherein the beer is a low-alcohol, reduced-alcohol or non-alcohol beer. 
     
     
         13 . The method according to  claim 1 , wherein the use of a  Pichia  spp. yeast strain in step c) increases the content of at least one flavor compound selected from the group consisting of isoamyl acetate, isobutyl acetate, ethyl propionate, ethyl valerate, ethyl octanoate and ethyl decanoate by at least 50%. 
     
     
         14 . The method according to  claim 1 , wherein the use of a  Pichia  spp. yeast strain in step c) increases the content of the thiol 3-mercaptohexyl acetate by at least 10%. 
     
     
         15 . The method according to  claim 1 , wherein when the at least one hop variety in step b) is any variety selected from the group consisting of Ahtanum, Amarillo, Apollo, Cascade, Centennial, Chinook, Citra, Cluster, Columbus, Crystal, Eroica, Galena, Glacier, Greenburg, Horizon, Liberty, Millenium, Mount Hood, Mount Rainier, Newport, Nugget, Palisade, Santiam, Simcoe, Sterling, Summit, Tomahawk, Ultra, Vanguard, Warrior, Willamette, Zeus, Admiral, Brewer's Gold, Bullion, Challenger, First Gold, Fuggles, Goldings, Herald, Northdown, Northern Brewer, Phoenix, Pilot, Pioneer, Progress, Target, Whitbread Golding Variety (WGV), Hallertau, Hersbrucker, Saaz, Tettnang, Spalt, Feux-Coeur Francais, Galaxy, Green Bullet, Motueka, Nelson Sauvin, Pacific Gem, Pacific Jade, Pacifica, Pride of Ringwood, Riwaka, Southern Cross, Lublin, Magnum, Perle, Polnischer Lublin, Saphir, Satus, Select, Strisselspalt, Styrian Goldings, Tardif de Bourgogne, Tradition, Bravo, Calypso, Chelan, Comet, El Dorado, San Juan Ruby Red, Satus, Sonnet Golding, Super Galena, Tillicum, Bramling Cross, Pilgrim. Hallertauer Herkules, Hallertauer Magnum, Hallertauer Taurus, Merkur, Opal, Smaragd, Halleratau Aroma, Kohatu, Rakau, Stella, Sticklebract, Summer Saaz, Super Alpha, Super Pride, Topaz, Wai-iti, Bor, Junga, Marynka, Premiant, Sladek, Styrian Atlas, Styrian Aurora, Styrian Bobek, Styrian Celeia, Sybilla and Sorachi Ace, the use of the  Pichia  spp. yeast strain in step c) will result in a flavor profile of levels of the flavor compounds isoamyl acetate, isobutyl acetate, ethyl propionate and ethyl valerate which is different from a flavor profile resulting from use of the  Pichia  spp. yeast strain in step c) when the hop variety in step b) is any other variety selected from the group consisting of Ahtanum, Amarillo, Apollo, Cascade, Centennial, Chinook, Citra, Cluster, Columbus, Crystal, Eroica, Galena, Glacier, Greenburg, Horizon, Liberty, Millenium, Mount Hood, Mount Rainier, Newport, Nugget, Palisade, Santiam, Simcoe, Sterling, Summit, Tomahawk, Ultra, Vanguard, Warrior, Willamette, Zeus, Admiral, Brewer's Gold, Bullion, Challenger, First Gold, Fuggles, Goldings, Herald, Northdown, Northern Brewer, Phoenix, Pilot, Pioneer, Progress, Target, Whitbread Golding Variety (WGV), Hallertau, Hersbrucker, Saaz, Tettnang, Spalt, Feux-Coeur Francais, Galaxy, Green Bullet, Motueka, Nelson Sauvin, Pacific Gem, Pacific Jade, Pacifica, Pride of Ringwood, Riwaka, Southern Cross, Lublin, Magnum, Perle, Polnischer Lublin, Saphir, Satus, Select, Strisselspalt, Styrian Goldings, Tardif de Bourgogne, Tradition, Bravo, Calypso, Chelan, Comet, El Dorado, San Juan Ruby Red, Satus, Sonnet Golding, Super Galena, Tillicum, Bramling Cross, Pilgrim. Hallertauer Herkules, Hallertauer Magnum, Hallertauer Taurus, Merkur, Opal, Smaragd, Halleratau Aroma, Kohatu, Rakau, Stella, Sticklebract, Summer Saaz, Super Alpha, Super Pride, Topaz, Wai-iti, Bar, Junga, Marynka, Premiant, Sladek, Styrian Atlas, Styrian Aurora, Styrian Bobek, Styrian Celeia, Sybilla and Sorachi Ace.