Why Ground Flax Seed Takes Up More Space: The Science Behind It

[clinden]

Why does ground flax seed consume about 30% more volume than whole flax? It would seem to me the finer particle size would result in the ground requiring less volume, as the "sphere packing" inefficiencies would be less?

 

[BillTre]

You have a reference for this?
Is this something that does not occur in the grinding up of other seeds/nuts?

Perhaps inside the seed shell, the contents are:

• under pressure and expand when released from the shell (kind of like pop-corn), causing a rapid expansion.
• kept separate from the surrounding environment. When released from the shell, the contents cen react with their surroundings (like, perhaps, water in the air (humidity)) and swell up due to the added mass. This would result in a delayed and environment dependent expansion.

 

[clinden]

You have a reference for this?
Is this something that does not occur in the grinding up of other seeds/nuts?

Perhaps inside the seed shell, the contents are:

• under pressure and expand when released from the shell (kind of like pop-corn), causing a rapid expansion.
• kept separate from the surrounding environment. When released from the shell, the contents cen react with their surroundings (like, perhaps, water in the air (humidity)) and swell up due to the added mass. This would result in a delayed and environment dependent expansion.

No reference-just my experience from grinding 8 ounces of seed this afternoon.

 

[BillTre]

Interesting question.
You packing argument seems good to me, but I'm not particularly knowledgeable about these things.

Does the weight change?
What if you crush it down? Maybe the small particle spring out branches pushing them apart. (look under a microscope)

 

[clinden]

Interesting question.
You packing argument seems good to me, but I'm not particularly knowledgeable about these things.

Does the weight change?
What if you crush it down? Maybe the small particle spring out branches pushing them apart. (look under a microscope)

Plausible sounding ideas.
Crushing down doesn't do much. Ground and whole both pretty much in-compressible.
Kitchen scale shows no discernible weight difference.

 

[DaveC426913]

If you dig hole with dirt and then try to fill that hole with the same dirt, you will invariably have some dirt left over. The dirt - which was very tightly compressed before - is now mixed with air, and poorly packed.

I think heart of the issue us that whole flax seed is hard and smooth, and will very easily slip into an efficient packing arrangement. Ground seed is fibrous and spongy and will initially pack very loosely as the various fibrous bits grab each other - it will not easily settle to a more efficient packing arrangement.

Given time and a bit of encouragement though, it will likely settle into a more compact form than the whole seed.

This is my opinion.

 

[DaveC426913]

I wonder if packing efficiency is related to angle of repose.

Try an experiment. Pile up a cone of whole flax seed next to a cone of ground flax seed and see if there is a difference in the angle of repose.

I predict the ground seed will have a steeper angle of repose.

 

[clinden]

If you dig hole with dirt and then try to fill that hole with the same dirt, you will invariably have some dirt left over. The dirt - which was very tightly compressed before - is now mixed with air, and poorly packed.

I think heart of the issue us that whole flax seed is hard and smooth, and will very easily slip into an efficient packing arrangement. Ground seed is fibrous and spongy and will initially pack very loosely as the various fibrous bits grab each other - it will not easily settle to a more efficient packing arrangement.

Given time and a bit of encouragement though, it will likely settle into a more compact form than the whole seed.

This is my opinion.

This too makes sense. More so than my original premise that finer particles (spheres) should pack more efficiently. In reviewing some sphere packing algorithms, I now find that the radius of the sphere does not affect packing efficiency.
Rather, the packing algorithm seems to be all that matters, once you ignore edge effects, i.e., as the total volume packed
goes to infinity, efficiency is independent of radius.

 

[BillTre]

Interesting comparison.

However, angle of repose could increase due to changes (increases) in the surface stickiness of the particles.
Ground up moist (or maybe oily) particles vs. the smooth dry looking surface of the seed's exterior.

Wet sand vs. dry sand.
Same particles, different stickiness (maybe due to capillary action of the water between the particles?), different angle of repose.

 

[256bits]

Plausible sounding ideas.
Crushing down doesn't do much. Ground and whole both pretty much in-compressible.
Kitchen scale shows no discernible weight difference.

Within the flax kernel you have a densely packed amount of material.
Packing the kernels in bulk there is a particular void/ material ratio.

Breaking the kernel in 2, 3 or more pieces allows voids to become available when packed in bulk changing the density. The pieces do not align up only at the breakages but in random fashion.
Up to certain limit in which you grind the particles to a fine powder the void/material ratio should begin to decrease up the point where you have ground the material to atom or molecular size whereupon the density of a small sample will be similar to that of a kernel - the greatest achievable. Packing that and you could have a result where the packed powdered bulk density is greater than packed kernel density.

Kind of like having a block of steel which is dense and has no voids.
Cut into chunks, and stacking in random manner, voids appear amongst the chunks decreasing the density.
You would have to cut into atom size again to get back to the steel block density once more.

The thing is, the chunks or pieces are not spherical, not of the same shape or exact copies of the original piece.
it is most likely though a function of original piece shape.

that is how I see it.

 

[davenn]

More so than my original premise that finer particles (spheres) should pack more efficiently

you have said spheres several times
why do you think they would be spheres ?
Have you looked in a microscope ?
I would have expected the particles to have irregular shapes

 

[clinden]

No microscope. I said spheres as a simplifying assumption to enable me to think about the problem
by drawing upon the well-studied sphere packing problem.