Dear Ruth and Jessica,
I am a little confused about Ruth’s answer – Ruth’s answer is sort of right, but mixes up weight (actually mass) and volume, and especially, I am confused about Ruth’s comment about recording your altitude.
It is true that you weigh less on the top of Mount Everest than at the bottom of Death Valley, but - in connection with food density - is that something a normal kitchen scale can measure – I doubt it.
The boiling point of liquids is influenced by the altitude and the differences are measurable, but that is a completely different story.
Density is mass per volume and always has a unit (g/cm3, kg/m3, kg/litre, tonnes/m3, etc.).
You can use ordinary standard, household measures, cup, teaspoon, decilitre/litre measures, etc.
I think that what Ruth is trying to say is that you can actually use any glass or container – and I would say the bigger the better to minimize errors in measuring.
1. Weigh the container without anything in it.
2. Top fill the container with water from fridge or just cold tap water (in my country it is ground water and always 8 degrees).
3. Weigh the water+container – the difference in mass water+container minus mass of container is a measure of the volume of water as the density of water is about 1 g/cm3, i.e. if you find that the mass of water in the container is 526 gram, then the volume is (about) 526 cm3.
4. Then fill the container to the top with the food in question and weigh it. The mass of the food is the mass of container+food minus the mass of the container.
The density can then be calculated as mass of food divided by the volume of the container, e.g. if the mass of food is 428 g and the volume of the container is 526 cm3, the density of you food is 428 g divided by 526 cm3 which equals 0.814 g/cm3 or 814 g/litre or 0.814 kg/litre.
All the best,
Anders
PS. Just as a precaution, please do not mix up density and specific gravity (which is without unit) – see earlier posts in the group.
Anders Møller
Danish Food Informatics
Borgediget 12
DK-4000 Roskilde, Denmark
From: Food Composition Discussion Group [mailto:[log in to unmask]] On Behalf Of Charrondiere, Ruth (ESN)
Sent: 11 May 2015 16:43
To: [log in to unmask]
Subject: Re: Best Practices for Calculating Density Conversion Factors
Dear Jessica,
you take a laboratory scale, put an empty glass or other container on it, weigh it. Then fill it up with water coming from the fridge. weigh it. Record the difference in weight which is your volume. Then weigh all foods in this container and divide it by the volume. Describe the food well, e.g. fish powder, loose; raw eggplant without skin in 1 cm cubes. Record your location (altitude). I would be happy to include your data in our next version of the FAO/INFOODS density database
Best wishes
Ruth
P.S. Anyone else willing to contribute data are most welcome
From: Food Composition Discussion Group [[log in to unmask]] On Behalf Of Raneri, Jessica (Bioversity) [[log in to unmask]]
Sent: Monday, May 11, 2015 2:12 PM
To: [log in to unmask]
Subject: Best Practices for Calculating Density Conversion Factors
Dear Infoods Members,
We’re currently attempting to identify the density conversion factors of some unique foods in Vietnam in order to analyse 24hr recall data. Is anyone aware of guidelines or best-practices manual on how to calculate these densities? We would like to eventually make the data publically available.
Many thanks in advance.
Jessica Raneri, MSc
Nutritionist, Research Support Officer
Nutrition and Marketing Diversity Programme,
Bioversity International
Via dei Tre Denari, 472/a
00057 Maccarese (Fiumicino)
Rome, Italy
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