AW Measurement in Handling of Seeds

When we think about forest conservation, one of the first thoughts that come to mind is avoiding damage. Such as the damage caused by roads, electrical lines, mines or littering. However, forests must also cope with natural issues such as fire, disease, invasive species and warming temperatures.

A way to help forests be more sustainable is trying to exploit their natural potential, so they can grow fully in difficult conditions. In this regard institutions around the world run programs for the protection of the genetic health of forest trees species. By studying the genetics of forest trees, it can be determined which ones are more resistant to changes in weather conditions, certain diseases or plagues.

Seeds Storage and Conservation

This knowledge is used to gather, analyse and conserve seeds which can be used to reforest damaged zones or to revitalize selected areas. Thus helping forests against the environmental stresses that affect reproduction, growth and productivity of forest trees as well as the survival of its ecosystems.

The moisture content of the seed affects to the type of treatment it could need. Moisture is related to its degree of maturity and it is crucial for the longevity in storage.

The storage conditions play a vital role in maintaining the moisture content of the seeds since depending on the temperature and humidity of the storage environment, the seeds will loose water to the air or absorb it, until reaching the equilibrium with the air.

In the past, the method to calculate seed moisture consisted in weighing the seeds, drying them in an oven for several hours and weighing them again to measure the weight difference. The issue with this way of measuring the seed moisture is that the high temperatures required to dry the seeds would harm its germination capabilities.

AW-Measurement for Sensitive Seeds

Water activity measurement (aw) or in other words, the equilibrium of Relative Humidity (eRH), is a non-destructive method widely used in the seed industry for moisture management.

Water activity or equilibrium relative humidity is usually defined as the percent relative humidity generated in equilibrium with the product sample in a closed system at constant temperature.

ERH = 100 x a_w  

Therefore, a_w can be measured with a relative humidity sensor provided that the conditions specified in the above definition are fulfilled.

Practical Conditions for Measuring Water Activity

Leak proof measurement chamber: closed system.

Volume ratio: air/product. The volume of air must be kept to a minimum: a small air volume reaches equilibrium with the sample faster than a large air volume

Temperature homogeneity: any temperature difference between the sensor, the chamber and the sample will result in significant errors. The higher the aw value the greater the error will be (a 0.8a_w at 25°C with a 1°C temperature difference can result in an error of 0.05a_w).

Constant temperature needs to be kept.

Equilibrium time: in order to read the correct water activity value, equilibrium needs to be reached! The higher the a_w the longer it takes!

Calibration of the sensor: using traceable humidity standards.

Learn more about Water Activity Measurement in our explain-it Video: