Measuring the moisture content on the fruits

05-09-2025

“During the past couple of years, growers on Lake Constance have been regularly faced with long, dry periods in summer, combined with a lack of water to irrigate the trees”, Sarah Gruntmeir said during the KOBstbautag in Bavendorf on the German side of Lake Constance on 17 July. To optimally use the scarce water, an insight into the need for water of the trees is essential. Measuring the moisture condition can be done in three ways:

1. Measuring the moisture condition in the soil with the help of sensors that measure the suction power or the volumetric volume of soil moisture. 
2. Measuring fruit growth during the day with a dendrometer, the water transport through the stomata with a porometer, or the water pressure in the trancheae (xylem) of the stem.
3. Measuring the volume of water in the fruit with an optic measuring device. 

In principle, the last-mentioned method offers the best picture of what the fruits need. Sarah Gruntmeir researched this method and tested the Felix F-750 spectrometer. This device makes it possible to determine the moisture content in the fruit from 8 mm fruit diameter. A disadvantage is that at a price of around € 10,000 this device is rather expensive for this application. In cooperation with the German institute for applied photonics and optics (ILM), a prototype of a measuring device has been developed that can measure the water content in smaller fruits and on top of that is considerably cheaper. 

(Source: EFM September 2025)