Weighing Issues

[carrie71]

Ok...this is probably the most dumb question but here goes. So 12 oz of olive oil does not weigh 12 oz? If a recipe calls for 12 oz of olive oil, then it needs the oil in weight and not fluid oz?
I may need to go back to grammar school because I’m confused.

 

[Kcryss]

Ok...this is probably the most dumb question but here goes. So 12 oz of olive oil does not weigh 12 oz? If a recipe calls for 12 oz of olive oil, then it needs the oil in weight and not fluid oz?
I may need to go back to grammar school because I’m confused.

Maybe you're looking at something showing the difference between weight and volume. With soap, it's best to use a scale and actually weigh everything. Volume can vary based on density etc.

 

[carrie71]

Maybe you're looking at something showing the difference between weight and volume. With soap, it's best to use a scale and actually weigh everything. Volume can vary based on density etc.

Thank you so much for your reply. I have a brand new digital scale. I placed the measuring container on it then hit tare. I filled it to the 12 oz mark but it weighed out at 9 something on the scale. Does this sound right?

 

[Kcryss]

Thank you so much for your reply. I have a brand new digital scale. I placed the measuring container on it then hit tare. I filled it to the 12 oz mark but it weighed out at 9 something on the scale. Does this sound right?

Yes, it does. Different liquids and even dry ingredients as well weigh different based on density, water content (dry ingredients) and probably a few other things as well. That's why weighing ingredients for soap making is critical to successful soaping. Great that you have a new scale.

 

[shunt2011]

It doesn’t matter what the lines say, just be sure to weigh everything you’re using and you won’t go wrong. Unless the scale isn’t accurate. If a bottle states ounces, then it should weigh in at that amount.

 

[Kcryss]

Thinking about it though ... that is a huge difference. You might want to verify the accuracy of the scale.

 

[carrie71]

I did try it with water on my scale. And 8 oz of water weighs 8oz on the scale.
However, it’s taking 14 oz of olive oil to weigh in at 12 oz.
Can it be the type (extra virgin) of oil?

 

[Kcryss]

I would have to run upstairs and see what mine shows when I weigh it out. I can do that in 30 min when I get off work.

 

[carrie71]

You’re a lifesaver!

 

[amd]

Keep in mind that you are dealing with two different types of measurements:
Fluid Ounces = Volume
Ounces = Weight
http://www.differencebetween.net/sc...s/difference-between-fluid-ounces-and-ounces/

However, it’s taking 14 oz of olive oil to weigh in at 12 oz.
Can it be the type (extra virgin) of oil?

Water is unique in that the fluid ounces (volume) is equal to the ounces (weight). Oils typically are not equal between volume and weight... or equal to each other for that matter. For example it takes a lot less volume of castor oil to equal the same weight as Sunflower oil (sunflower oil will more volume), because castor oil is heavier. So while your OO type might have slight differences comparing volume to weight (Pomace OO might have less volume for the same amount of weight as say EVOO), that isn't the problem in your case. The difference really is that fluid ounces is not the same as weight ounces.

Keep in mind that SAP values are set by weight of oil to weight of lye, so it is important to follow weights and not volume.

 

[carrie71]

That makes sense now. I think with more homework and experimentation, I might get a handle on this. This is my first cold process recipe. We’ll see what happens!

 

[Kcryss]

I did try it with water on my scale. And 8 oz of water weighs 8oz on the scale.
However, it’s taking 14 oz of olive oil to weigh in at 12 oz.
Can it be the type (extra virgin) of oil?

I weighed EVOO - 4.2 oz by weight and 4 oz by volume.

 

[carrie71]

Thank you so much! I’m not sure where I’m messing up but I’ll figure it out eventually. You’ve been a great help though!

 

[Kcryss]

Happy to help.

 

[DeeAnna]

Fats have a specific gravity of about 0.92. Water has a specific gravity of 1.0.

8 volume ounces of water weigh 8 weight ounces
8 volume ounces of fat weigh 0.92 X 8 = 7.4 weight ounces

14 volume ounces of fat weigh 0.92 x 14 = 12.9 oz

Remember also that measuring volume in a measuring cup is really, really inaccurate for the purposes of making soap. If you're measuring a weight of 12 weight ounces for 14 volume ounces of fat, the difference of 0.9 wt oz was caused by how inaccurate your measuring cup is.

If you convert your recipes to grams, all this confusion magically disappears. I recommend it.

 

[SmockingRN]

Dear Deanna, You have helped me so much with my many questions. Thank you, thank you, thank you!

 

[jcandleattic]

oil in weight and not fluid oz?

Fluid oz is volume, not weight. ALWAYS weigh the oils in weight.
Remember your elementary teachings - which weighs more, 1lb of bricks, or 1lb of feathers? Well, they will both WEIGH the same, but the volumes will be drastically different. Same with oils. The specific gravity and density of each oil will be slightly different so they will not weigh the same even if their volumes are the same.

Some of this may have already been covered in other posts, but I only read this question before replying.

 

[MGM]

If you convert your recipes to grams, all this confusion magically disappears. I recommend it.

Not just in soap-making, in EVERYTHING. Baking especially.
Also, using metric makes a lot more sense, too.
But old habits die hard in some parts of the world...

 

[JakeBlanton]

Keep in mind that you are dealing with two different types of measurements:
Fluid Ounces = Volume
Ounces = Weight
http://www.differencebetween.net/sc...s/difference-between-fluid-ounces-and-ounces/


Water is unique in that the fluid ounces (volume) is equal to the ounces (weight). Oils typically are not equal between volume and weight... or equal to each other for that matter. For example it takes a lot less volume of castor oil to equal the same weight as Sunflower oil (sunflower oil will more volume), because castor oil is heavier. So while your OO type might have slight differences comparing volume to weight (Pomace OO might have less volume for the same amount of weight as say EVOO), that isn't the problem in your case. The difference really is that fluid ounces is not the same as weight ounces.

Keep in mind that SAP values are set by weight of oil to weight of lye, so it is important to follow weights and not volume.

Actually, 1 fluid ounce of water does not weight exactly 1 ounce.

With the metric system, 1 ml of water at 4C was *supposed* to weigh 1 gram, but because of unit redefinitions over the years, that is not entirely accurate anymore either. Nothing wrong with the metric system, but there is nothing intrinsically special about it. It's just another arbitrary scale they they just happen to use powers to 10 to define multiples.

Water has a density of 999.9720 kg/cu-m or 0.9999720 g/ml. Not exactly 1g/ml, but pretty close.

A gallon (liquid) has 128 fl-oz in it or 231 cu-in (exactly).

A pound is legally defined as 453.59237 g.

There are 2.54 cm per inch (exactly).

1 cc (cubic centimeter) = 1 ml (exactly).

Therefore, a gallon (liquid) = 231 * 2.54 * 2.54 * 2.54 = 3785.411784 ml

Since there are 128 fl-oz in a gallon (liquid), 1 fl-oz = 29.5735295625 ml

And since water weighs 0.9999720 g/ml, this means that 1 fl-oz weighs 29.57270150367249 g.

So, 1 fl-oz weighs 29.57270150367249 (grams) / 453.59237 (grams/lb) * 16 (oz/lb) = 1.043146347587 oz (weight).

An ounce (force) is different than an ounce (liquid) and that is also different than an ounce (dry volume).

So, the old adage "a pint of water equals a pound" is not quite right... It's more like a pint of water equals 15.338212 oz (weight).

Not just in soap-making, in EVERYTHING. Baking especially.
Also, using metric makes a lot more sense, too.
But old habits die hard in some parts of the world...

There's noting magic about the metric system. It's just another arbitrary system of measurements. The issue here is not metric vs "US Customary" measuring systems, but measuring things by volume instead of weight of not understanding that there is a difference between volume units and weight units that are often referred to by the same name. When someone says "ounces", are they talking about ounces of force (weight), ounces of liquid volume, or ounces of dry volume? Many people don't even know that there are 3 different types of ounces in the "US Customary" system of measurement (and I'm not even going to include the UK's Imperial measuring system in this discussion). For baking, if you truly want consistent results, you should measure your ingredients by weight. It doesn't made a difference whether you are using the US's system or the metric system. You just need to know your system of measurement and be consistent in the use of it.

Fats have a specific gravity of about 0.92. Water has a specific gravity of 1.0.

8 volume ounces of water weigh 8 weight ounces
8 volume ounces of fat weigh 0.92 X 8 = 7.4 weight ounces

14 volume ounces of fat weigh 0.92 x 14 = 12.9 oz

Remember also that measuring volume in a measuring cup is really, really inaccurate for the purposes of making soap. If you're measuring a weight of 12 weight ounces for 14 volume ounces of fat, the difference of 0.9 wt oz was caused by how inaccurate your measuring cup is.

If you convert your recipes to grams, all this confusion magically disappears. I recommend it.

And remember that there are 2 different volume ounces -- fluid ounces and dry ounces...

A dry pint is 33.6003125 cu-in (exactly).

A fluid pint is 28.875 cu-in (exactly).

https://en.wikipedia.org/wiki/Pint

 

[DeeAnna]

We're talking about measuring ounces by weight and ounces by volume, not about measuring in pints.

And even if we were discussing measuring in pints, I've never heard of anyone in recent decades actually using dry pints as a unit of measure -- that's pretty outmoded. Dry materials like flour and sugar are sold by weight, not by volume. And most everyday people use cups, not pints, for measuring small volumes, regardless of whether the material is dry or liquid.