Fatmeter Measurements vs Foss-Let Chemical Method

Introduction

If you wish to the accuracy of the Fatmeter Measurements, and compare the results with Foss-Let Laboratory Analysis Method for an accurate appraisal of its performance, it is essential that the techniques employed are the same as those from which the original calibration data were derived.

When checking the calibration of the Fatmeter against the Foss-Let Method a key element in the process is the preparation of fish samples for these determinations. The purpose of this note is to describe the procedures to be used in the preparation of these samples. For detailed instructions please refer to the User Manual and calibration charts supplied with the meter.

Background

In attempting a calibration check of the Fatmeter, there are THREE points which must be understood. These are:

  • The Fatmeter is primarily intended as a tool for the Processor, Fish Farmer, or Researcher. It provides a non-destructive estimate of the fat content of the fish, or fish section. Please refer to measurement instructions for the product.
  • The Fatmeter is an averaging instrument and except in clearly defined circumstances will not make accurate measurements of the fat content of smaller, single fish eg. Herring and Mackerel, which require readings to be averaged from each of EIGHT fish randomly selected from a batch, before the specified accuracy of the instrument can be achieved. On the other hand, the fat content of a single large fish such as Salmon, can be assessed accurately if FOUR readings are taken from EACH side of the fish. These are then averaged by the instrument to provide an estimate of the fat content representing the trimmed fillets of the fish.
  • All fat content measurements used in the preparation of the calibration data for the Fatmeter were obtained using a Foss-Let Oil Meter. This requires 22g sample of fish flesh to be used. To allow for losses in mincing, sample of fish muscle with a minimum weight of 60g are required. It is advisable to prepare enough minced material in case a duplicate Foss-Let measurement is required, so that a sample of at least a 100g in weight is desirable. It is also good practice to carry out triplicate Foss-Let measurements on each filtrate. Any contamination of the filtrate or of the Foss-Let itself will then be immediately apparent.