Patent Application
20110223642
The present invention relates to an improved method for inhibiting gram positive bacteria growth and improving the alcohol yields during yeast propagation and ethanol fermentation by treatment with an antibacterial hop product, and to an improved antibacterial hop product, and to a method for making an improved antibacterial hop product. The antibacterial hop product is made by isomerizing alpha acids inside hops into a more water soluble antibacterial isoalpha acid. The antibacterial hop product can be added to a yeast propagator as it relates to yeast or gram negative bacteria growth and/or a fermenter as it relates to ethanol production via yeast or gram negative bacteria. It can also be added to any other stage of the process where gram positive bacterial infection needs to be suppressed.
Fermentable ingredients such as cereals, fruits, starches and canes/beets often arrive from the field contaminated with bacteria. The bacteria concentration can be reduced with washing but not eliminated. High cooking temperatures are often employed to further reduce the bacteria load; however, in some cases this is not practical or it is costly. When these fermentable ingredients are added to a yeast propagator or fermenter the residual bacteria can grow and compete with the yeast for nutrients and fermentable sugars. The result can be a reduction in overall alcohol yield, production of off-flavors or incomplete fermentation. Antimicrobials such as hop acids and other antibiotics often are employed at distilleries to inhibit the growth of gram positive bacteria during yeast propagation and/or fermentation. The gram positive bacteria that commonly infect fermentation streams are lactic acid producing bacteria of the genus Lactobacillus and Pediococcus. Aqueous alkaline solutions of hop acids currently are the only food grade antimicrobial used in distillery mashes; however, they can cost more than antibiotics making them expensive to use. In accordance with prior art practices, these aqueous alkaline solutions are made by extracting hops with CO2 followed by alpha acid isomerization, isoalpha acid isolation and followed by product formulation. The current invention eliminates the need for CO2 extraction, isoalpha acid isolation and product formulation. The antibacterial hop product is made by performing solid state chemistry by mixing hop powder with a metal base or oxide followed by pelletization and heating. In addition, most fuel ethanol plants only treat their propagators with an antibacterial. Once that propagator is added to a fermenter, the antibacterial gets diluted to a point where its antibacterial effect is lost. That is not the case with iso-pellets.
The present invention solves the need for inhibiting gram positive bacteria growth during yeast propagation and or fermentation cost effectively. Dry hop cones can be ground into a powder and blended with various alkali earth metals or alkaline earth metals or their oxides, bases, carbonates or bicarbonates to form a stabilized hop pellet. The stabilized hop pellets are salts of hop acids, generally salts of alpha acids. By warming these salts, to a temperature of 40° C. to 100° C., preferably about 70° C. to 90° C., more preferably about 80° C., e.g., in a hot room, the alpha acids undergo a thermal isomerization to form isoalpha acids thus forming an isomerized hop pellet also known as iso-pellets. We unexpectedly discovered that by adding antibacterial iso-pellets made in accordance with the present invention we obtained better antibacterial inhibition than by adding an equivalent amount of isoalpha acids alone. While not wishing to be bound by theory, we believe this better antibacterial inhibition is due to a secondary effect caused by other antibacterial compounds in hops such as beta acids and Xanthohumol. In addition it was discovered quite unexpectedly that the yeast became more alcohol tolerant when iso-pellets were used vs. iso-alpha acids alone.
The present invention is described herein with reference to the accompanying drawings, in which similar reference characters denote similar elements throughout the several views. It is to be understood that in some instances, various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.
The present invention is especially suitable for use in forming stabilized hop products useful in fermentation processes, and will be described with such utility.
Referring to
The resulting isomerized hop pellets are not very soluble in cold or warm water; however they are very soluble in hot water of temperatures over 50° C., preferably over 70° C. Once the isomerized hop pellets are dissolved in hot water they can be added to a yeast propagator and or fermenter at a dose rate of approximately 20 ppm to 300 ppm, preferably about 125 ppm based on 12% isoalpha acids. If added just to a propagator the isopellets should be diluted down to 2 to 20 ppm in a fermenter. The hop acids employed are not limited to isomerized hop acids but can also be stabilized unisomerized hop pellets. The stabilized hop pellet, can be isomerized into isoalpha acids once placed into 70° C. or hotter hot water for thirty or more minutes. Once this isomerization is completed the mixture can be added to the yeast propagator or fermenter. The unexpected results include reduced levels of isoalpha acid required to inhibit gram positive bacteria growth, better antibacterial protection toward the end of fermentation, and increased yeast alcohol tolerance. Typically about 15 ppm of isoalpha acid is required to inhibit most gram positive bacteria growth in a typical corn mash media; however, we discovered that isomerized hop pellets made in accordance with the present invention can inhibit bacteria growth at an isoalpha acid dosage of about 12 ppm. While not wishing to be bound by theory, it is believed iso-pellets made in accordance with the present invention also contain beta acids, which are very effective at inhibiting gram positive bacteria growth. Unfortunately beta acids ordinarily are not soluble in corn mash or cereal fermentations, and thus their antibacterial effect is worthless. Surprisingly, we unexpectedly discovered that as the fermentation proceeds and the alcohol yields increase, the alcohol solubilizes the beta acids allowing it to inhibit bacteria growth toward the end of fermentation. This unexpected benefit allows one to inhibit bacteria growth at the start of fermentation with iso-alpha acids and at the end with beta acids making iso-pellets more cost effective to use. This observation also leads to the discovery that if we dissolve the iso-pellets in a water/alcohol solution, it dissolves essentially all the actives in the iso-pellets, whereas with water only, it seems to dissolve essentially only just the iso-alpha acids. Preferably the alcohol comprises a lower alcohol, e.g. containing 1 to 6 carbon atoms, more preferably, methanol, ethanol, propanol or the like, or a mixture of lower alcohols. Of course, in the case of a fermentation process for producing a food product or beverage, the alcohol should be food compatible. Generally, the alcohol is present in an amount of 20% to 80% w/w alcohol/water, more preferably 40% to 60% w/w alcohol/water, most preferably 50%% w/w alcohol/water. Another unexpected benefit was increased alcohol tolerance of the yeast. Hops contain polyphenols and prenylasted flavanoids which are known to have antioxidant properties. Many fuel ethanol plants have difficulty achieving alcohol yields higher than about 17.5% w/w due to alcohol stress. Advantageously, the antioxidant properties of hop polyphcnols extends yeast life allowing the yeast to produce alcohol yields consistently higher than one would normally experience.
For clarity of disclosure, and not by way of limitation, the detailed description of the invention is divided into the subsections set forth below.
5.1. How The Antibacterial Isomerized Hop Pellet is Used
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The following examples are offered by way of illustration and not by way of limitation.
A trial was conducted at a batch fermentation, dry mill, fuel ethanol plant comparing the alcohol tolerance alcohol yield of fermenters treated with a purified solution of isoalpha acids vs. Iso-pellets. 4-kg of 30% Iso-alpha acid (containing 70% water) were added to each fermenter and compared to fermenters treated with an equivalent amount of isoalpha acids via iso-pellets (10-kg of Iso-Pellets containing 12% isoalpha acids). The trial was conducted over multiple fermentations and in each an every case, the Iso-pellet treated fermenters showed on average a 0.1% increase in alcohol yield vs. the 30% isoalpha acid treated fermenters. Yeast will only produce more alcohol if it is more tolerant to alcohol. We believe this increase in alcohol yield is due to the antioxidant polyphenols compounds found in Iso-pellets as well as the enhanced antibacterial effect that comes from the other compounds found within Iso-Pellets like beta acids and xanthohumol. That increase in alcohol yield is equivalent to 750 additional gallons per fermenter based on a fermenter size of 750,000 gallons. Therefore a typical 50 million gallon fuel ethanol plant could experience 375,000 gallons of additional ethanol per year by using Iso-pellets vs 30% Iso-alpha acids.
5.00 g of P-249-09 iso-pellets, made as in Example 1 where placed in a 100 mL beaker. To the pellets, 45.0 g of 50% ethanol was added at 20 C, 30 C, 40 C and 60 C to make a 10% Iso-Pellet Slurry. The pellets were stirred with a Teflon stir bar and the temperature was maintained within IC. 2.5 g aliquots were filtered through a 0.45 μm syringe filter with a cotton pre-filter at 5, 10, 20, and 30 min; then diluted to 50 mL with acidic methanol for HPLC analysis.
Results are reported in Table 2 and Plotted in
Other modifications and variations of this invention will occur to those skilled in the art in the light of the above description. It is to be understood, therefore, that changes may be made in the particular embodiments described herein which are within the full intended scope of the invention as defined in the appended claims.
This Application claims priority from U.S. Provisional Application Ser. No. 61/312,987, filed Mar. 11, 2010, the contents of which are incorporated herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61312987 | Mar 2010 | US |
