Assay accuracy in malt
How accurate and repeatable is our assay for malt?
Introducing the new SIRIUS platform
It is important to mention the organizations that oversee the certified quality methods. These methods are considered the standards that most malthouses and customers use and request.
EBC, the European Brewery Convention, and ASBC, the American Society of Brewing Chemists, are the organizations that set the industry standards for quality check methods. They also describe and set the repeatability and reproducibility criteria. At GlycoSpot, we always reference the results of our method with the ones obtained using EBC analytical methods.
What is repeatability?
You need to be able to achieve the same result, using the same method, in the same lab environment with the same team of operators. This means that you should be able to get the same result under the same conditions.
On the other hand, when it comes to reproducibility, we are comparing different laboratories with different teams that are using the same method. Can a method carried out in one lab environment be compared to the same method done in a different lab environment?
Common barley malt has a diastatic power value between 200 – 600 °WK. Although for most producers it is rather between 250 and 350 °WK. The repeatability (r95) range defined by EBC would be then between ±14 and ±28 °WK. Reproducibility (R95) wise, the range would be between ±51 and ±110 °WK.
For alpha amylase, regular barley malt has normally a value between 30 and 100 DU. In terms of repeatability, it translates into a range between ±2 and ±6.7 DU. In terms of reproducibility, it is already established by EBC to be ±10 DU for the whole 30-100 DU interval. With the GlycoSpot method, you can always achieve both r95 and R95 . A usual term used in the analytical world is “accuracy”, which is the ability to achieve the exact result/measurement. When it comes to EBC and malt in general, we have what we call ring trials. These consist of 10-50 different laboratories using EBC methods for diastatic power and alpha amylase. The average or median result is taken as the reference value or the “true” value.
Depending on how far you are from the reference value, then you can define the accuracy criteria. EBC sets a loose standard with reproducibility R95: because it is so wide (±51 to 110 °WK or ±10 DU), most malthouses do not consider a method accurate enough if it merely meets R95 criteria against reference values from ring trials.
Here at GlycoSpot, with the new Sirius platform, we can achieve the results obtained in different ring trials by different organizations, within a margin of ±20WK for diastatic power, and ±5 DU for alpha amylase, closer to r95 than R95 ranges. The following figure shows how the result of our method for diastatic power correlates well with ring trial reference values, with an R2>0.99:
What factors influence accuracy in malt?
Sampling. Milled malt is inherently inhomogeneous because some parts of the germinated grain (e.g. husk) have a lower enzyme concentration, whereas others have a higher concentration (e.g. endosperm). Furthermore, in the real world, most malthouses mix different batches of malt for storage, or to customize an order. The different degrees of inhomogeneity can be fixed by sampling in sub-batches and mix the sample well before and after milling.
Assay time. Since enzymatic activity is a kinetic parameter, incubation time (set at 7 minutes in GlycoSpot kits for malt) needs to be kept as consistent as possible.
Temperature control. Enzyme activity is very sensitive to temperature. Every 10 degrees of difference, the enzymatic activity doubles, or triples. A single degree could mean 7 – 10% difference. Our method is set at 35 degrees Celsius to cancel any effect of room temperature, which most commonly can oscillate from 15 to 30 °C. The heater rotator is included in our malt package, to ensure we can maintain the correct temperature.
Pipetting and weighing can also lead to error. For this reason, at GlycoSpot, we pre-measure the amount of buffer needed to run the assay, as well as the amount of extraction buffer, to minimize any error.