Display Title

Hops Methods​

Hops 1. Sampling

Hop samples may be required from bulk, unpressed, pressed, baled, or pellet lots or from “hop powders.” Each form requires a specific procedure to ensure a sample representative of the bulk lot and a preparation for laboratory analysis adapted to the material received. This method presents the basic procedures for obtaining representative samples of hops and preparing them for laboratory analysis.

Hops 2. Physical Examination

Hops are an agricultural commodity, and, as such, their sampling, inspection, and grading are regulated by the U.S. Department of Agriculture. Pertinent details related to the physical nature of the product in a lot (estimation of the proportion of leaves and stems in a sample; color; luster; size and condition of cones; amount, color, and condition of lupulin grains; aroma; and presence of seeds) are summarized in this method.

Hops 3. Aphids in Hops

The structural characteristics of hop cones and the conditions under which they are produced make them particularly vulnerable to aphid attack. Agricultural precautions are taken to prevent and minimize aphids’ presence in hops. This quality-assurance method serves as a laboratory check for their presence and damage level in hops.

Hops 4. Moisture

This method measures the moisture content (%) of hops by distillation, by vacuum drying, and by the routine air oven method. The most practical procedure for determining the moisture content of hops is with an air oven such as that used for malt moisture determination (see Malt-3). However, with hops, loss of other volatiles under heating conditions may be substantial. Accordingly, sample size, moisture dish dimensions, and heating time and temperature must be carefully regulated. The malt moisture oven may be used if the temperature setting is in lower part of permitted range. A distillation procedure is most accurate and should be used to check routine results obtained from the air oven method.

Hops 5. Resins

Analysis of hops for “soft” and “hard” resins is seldom required in the United States. Determinations are frequently requested for hops that are to be exported. This method provides references that describe recommended procedures.

Hops 6. α-and β-Acids in Hops and Hop Pellets

A major function of hops in brewing is to provide part of the constituents that characterize beer flavor. α-Acids are the primary precursors of bitter principles of beer and, as such, their evaluation becomes an important analytical procedure. ;Β-Acids, while essentially insoluble in the brewing process, also affect beer bitterness to a limited degree through their oxidation products. This method describes a spectrophotometric procedure that can be used to evaluate both α- and ;Β-acids and a conductometric procedure that is useful for evaluation of (-acids.

Hops 8. Non-Isomerized Hop Extracts

Introduction of concentrated liquid extracts of hops into brewing as a source of bittering substances requires analytical procedures adapted to such materials. The basic principles for evaluation are the same as those elaborated in Hops-6 and Hops-7, but provisions are required for reextraction of bittering substances from the concentrates. The organic solvent used for such partitioning is selected on the basis of efficiency, adaptability, and compatibility with safety requirements in laboratory use. A major distinction in method development depends on whether the extract is non-isomerized (Hops-8) or isomerized (Hops-9). Further, a “reduced” extract may be produced, e.g., one containing p-iso-α-acids. This method discusses analysis of hop extracts by isopropyl ether spectrophotometric and conductometric methods.

Hops 9. Isomerized Hop Extracts

Both this method and Hops-9D allow separation of isoadhumulone, isohumulone, and isocohumulone by high-performance liquid chromatography of diluted isomerized hop extract. The sum of the individual components provides a value for the total iso-(-acid content of the extract.

Hops 12. Hop Storage Index

When hop cones or hop products are subjected to prolonged or inappropriate process and storage conditions, an oxidative decrease has been observed in both α- and ;Β-acids content and has been found to be variety dependent. The loss coincides with a progressive increase in the ratio of absorbance at 275 nm (A275) to 325 nm (A325) when the alkaline methanol extract is evaluated with a UV spectrophotometer. Such loss in α- and ;Β-acids and increases in the hop storage index (HSI) ratio may reflect unfavorably on the utility and quality of the hops in brewing. This method calculates the HSI.

Hops 13. Total Essential Oils in Hops and Hop Pellets by Steam Distillation

This method determines total essential oils (mL/100 g) in hops and hop pellets by steam distillation.

Hops 14. α-Acids and β-Acids in Hops and Hop Extracts by HPLC (International Method)

This method utilizes reverse-phase high-performance liquid chromatography with ultraviolet detection to separate and quantitate cohumulone, n- + ad-humulone, colupulone, and n- + ad-lupulone in hops and hop extracts.

Hops 15. Iso-α-Acids in Isomerized Hop Pellets by HPLC 1993

This method involves the extraction of iso-α-acids from isomerized hop pellets that have been prepared by addition of magnesium oxide during pelleting, which continues the isomerization of the α-acids in the pellets by heating under vacuum. Because of the magnesium salts, an acid (phosphoric acid) is needed to maximize the extraction of the free iso-α-acids into the n-butyl acetate extracting solvent. The diluted solutions are analyzed by high-performance liquid chromatography.

Hops 16. Iso-α, α-, and β-Acids in Hop Extracts and Isomerized Hop Extracts by HPLC

In this method, high-performance liquid chromatography with variable-wavelength UV detection is used to simultaneously determine the concentrations of iso-α-, α-, and ;Β-acids in hop and isomerized hop extracts. Separation of these components is achieved with a C.18-reverse-phase column.

Hops 17. Hop Essential Oils by Capillary Gas Chromatography-Flame Ionization Detection

This method identifies and measures selected components of hop essential oil using a gas chromatograph equipped with a flame ionization detector. Estimated concentrations of several components may be determined using the optional internal standard.

Hops 18. Determination Of Tetrahydroiso-α-Acids In Hop Products By Spectrophotometry

The method for spectral determination of tetrahydroiso-α-acids in hop products described here can be used to determine the spectral concentration of these α-acids in hop products made from either α-acids or β-acids. The method offers a choice of extinction coefficient to be used depending on which type of α-acid is in the product.