A kitchen device comprising a food processing device or food storage device, the kitchen device comprising: a chamber for housing a liquid foodstuff to be processed or stored; and a nutrition analysis system, comprising: an electromagnetic radiation source; a radiation guide for guiding the electromagnetic radiation based on total internal reflection, wherein the radiation guide comprises an input coupled to the electromagnetic radiation source, an output, and a sensing surface between the input and output for placing against a liquid foodstuff to be analyzed, wherein the sensing surface is placed for direct or full contact with the liquid foodstuff, wherein the sensing surface is integrated into a wall of the chamber of the food processing device or food storage device, or wherein the sensing surface is arranged at a location along a food processing path of the food fudd processing device; a detector for detecting guided electromagnetic radiation at the output of the radiation guide; and a filter arrangement for wavelength filtering the guided electromagnetic radiation reaching the detector, wherein the filter arrangement comprises a plurality of optical bandpass filters (46a, 46b), and the plurality of optical bandpass filters are selectively movable into the path of the detector or there is a respective detector (44a, 44b) for each optical bandpass filter, wherein the kitchen device comprises (i) a blender or juicer, or (ii) a storage jar or storage bottle, wherein the storage jar or storage bottle are configured for keeping food warm or cold and the nutrition analysis system is configured for determining when the liquid foodstuff is becoming perished. a chamber for housing a liquid foodstuff to be processed or stored; and a nutrition analysis system, comprising: an electromagnetic radiation source; a radiation guide for guiding the electromagnetic radiation based on total internal reflection, wherein the radiation guide comprises an input coupled to the electromagnetic radiation source, an output, and a sensing surface between the input and output for placing against a liquid foodstuff to be analyzed, wherein the sensing surface is placed for direct or full contact with the liquid foodstuff, wherein the sensing surface is integrated into a wall of the chamber of the food processing device or food storage device, or wherein the sensing surface is arranged at a location along a food processing path of the food fudd processing device; a detector for detecting guided electromagnetic radiation at the output of the radiation guide; and a filter arrangement for wavelength filtering the guided electromagnetic radiation reaching the detector, wherein the filter arrangement comprises a plurality of optical bandpass filters (46a, 46b), and the plurality of optical bandpass filters are selectively movable into the path of the detector or there is a respective detector (44a, 44b) for each optical bandpass filter, wherein the kitchen device comprises (i) a blender or juicer, or (ii) a storage jar or storage bottle, wherein the storage jar or storage bottle are configured for keeping food warm or cold and the nutrition analysis system is configured for determining when the liquid foodstuff is becoming perished. an electromagnetic radiation source; a radiation guide for guiding the electromagnetic radiation based on total internal reflection, wherein the radiation guide comprises an input coupled to the electromagnetic radiation source, an output, and a sensing surface between the input and output for placing against a liquid foodstuff to be analyzed, wherein the sensing surface is placed for direct or full contact with the liquid foodstuff, wherein the sensing surface is integrated into a wall of the chamber of the food processing device or food storage device, or wherein the sensing surface is arranged at a location along a food processing path of the food fudd processing device; a detector for detecting guided electromagnetic radiation at the output of the radiation guide; and a filter arrangement for wavelength filtering the guided electromagnetic radiation reaching the detector, wherein the filter arrangement comprises a plurality of optical bandpass filters (46a, 46b), and the plurality of optical bandpass filters are selectively movable into the path of the detector or there is a respective detector (44a, 44b) for each optical bandpass filter, wherein the kitchen device comprises (i) a blender or juicer, or (ii) a storage jar or storage bottle, wherein the storage jar or storage bottle are configured for keeping food warm or cold and the nutrition analysis system is configured for determining when the liquid foodstuff is becoming perished. (i) a blender or juicer, or (ii) a storage jar or storage bottle, wherein the storage jar or storage bottle are configured for keeping food warm or cold and the nutrition analysis system is configured for determining when the liquid foodstuff is becoming perished.