How do you analyse hops?
Hops in their natural form are a very inhomogeneous product. There can be significant differences within the lots and even within a single bale. When analysing the various hop lots it is therefore essential to prepare the sample thoroughly in order to be able to analyse the alpha acids representatively. First of all the resins have to be extracted from the plant material by a solvent before a sample can be analysed for its valuable components.
The steps for analysing cone hops or hop products are generally as follows:
- Preparing the sample:
- taking the sample
- breaking up the large sample
- separating into individual samples
- Releasing the bitter substances:
- selecting a solvent
- selecting the suitable mixer or shaker
- clarifying the solution
- physical method / separation
- evaluating the measuring signal
Which analysis methods are available for hops and/or chemically not modified hop products?
The Analytica-EBC (2005) describes the following methods in Section 7 Hops:
To take samples and determine the moisture content :
EBC 7.1 Sampling of Hops and Hop Products
EBC 7.2 Moisture Content of Hops and Hop Products
For the analysis of bitter substances the EBC contains: 3 conductometric methods and 2 HPLC methods:
a) For cone hops and hop pellets the following are applied by conductometry:
EBC 7.4 Lead Conductance Value of Hops, Powders and Pellets
EBC 7.5 Bitter Substances in Hops and Hop Products: Ganzlin Modification of the Wöllmer Method
b) For hop extracts the following are applied by conductometry::
EBC 7.6 Bitter Substances in Hop Extracts: Ganzlin Modification of the Wöllmer Method
c) For all products but primarily for extracts using HPLC (High Performance Liquid Chromatography):
EBC 7.7 alpha and beta acids in Hops and Hop Products by
HPLC EBC 7.8 iso-alpha, alpha and beta acids in Hops and Hop Products by HPLC
Methods of Analysis
ASBC Methods of Analysis (1992) describes the following methods:
To determine the bitter content by means of spectral photometry
ASBC Hops-6: Alpha- and beta-acids in Hops and Hop Pellets by spectrophotometry and by conductometric titration
1) Spectral photometric method – IBU, EBC BU
The wort (or the beer) is shaken out with soured iso-octan. From the non-polar phase the absorption is determined by spectral photometry at 275 nm which is a function of the content of bitter components.
The result is converted into bitter units by using a formula.
Absorption at 275 nm = 0,5
IBU = 0.5 x 50 = 25 IBU
2) HPLC methods
As described in the EBC 7.8 method, alpha- and iso-alpha-acids can be precisely determined in wort and beer by means of a gradient HPLC. There are other gradient methods which are based on the same principle.