A question of weight

[John Harris]

When someone says they are making a 3 pound batch, for example, what are they referring to? Is it just the oils/butters they are counting or are they including the lye and water also?

 

[penelopejane]

I think people are generally referring to the mold size which is calculated on the total batter weight not just the oils.

 

[jcandleattic]

When I refer to my batches by weight I am always talking about oil weight only. However, it really depends on the person who is talking because as you see by the above post, it's not always by oils only, it really could be either.

 

[msunnerstood]

When I talk about it I am talking about the finished weight.

 

[DeeAnna]

I guess I talk about it either way, depending on the context. I think I usually say something like "a batch with 1600 grams of oils" or "a total batch weight of 2800 grams" or something like that.

 

[Obsidian]

For me it's the oil weight. I have no idea what my finished batches weigh.

 

[John Harris]

I am asking the question because I want to start making smaller experimental batches. I will be pouring into individual bar molds (4 or 6 bars per mold). Do I measure the volume of one cavity and multiply by the number of cavities?

 

[DeeAnna]

Yes, you do need to know the volume of the mold(s) you want to fill, but there's more to it than that.

Many people use the "0.40 rule" for weight ounces and inches or the "0.70 rule" for grams and centimeters to determine the batch size needed to fill the mold(s). For either of these rules, the answer you get will be the weight of fats, not the total batch weight.

More about these rules here on SMF:
https://www.soapmakingforum.com/threads/how-to-figure-how-much-oil-for-mold.2909/
https://www.soapmakingforum.com/threads/using-40-to-calculate-my-soap-mold-oils.58581/

Article I wrote about these rules: https://classicbells.com/soap/moldBatchSize.asp

 

[TheGecko]

When someone says they are making a 3 pound batch, for example, what are they referring to? Is it just the oils/butters they are counting or are they including the lye and water also?

That's a really good question because while I have one and two 'pound' molds, they hold more than that. As an example, the recipe for my 1-lb mold is 16 oz of oils plus 7.37 oz of lye solution for a total weight of 23.37 oz. Plus I add in at least 1 tea Sodium Lactate and 1 tea Kaolin Clay which may take it up to 23.5 oz and that tops out my mold. My 2-lb mold tops out with approximately 48.5 oz total weight; 33 oz of oils, 15.5 oz lye solution. I don't like topping out my molds because it makes them hard to move, so I always take enough out to fill one of those single cavity molds you can buy in a 16-pack on Amazon. So while the total weight of my batch is obviously more than 16 or 32 oz, I refer to it as a one or two 'pound' because of a combination of mold size/oil weight.

But I'm really glad that you asked the question, because it's been sitting in the back of my mind to ask too because I've been kind of winging it with some of my other molds as in...let's make a 1-lb batch and see how many of x-molds it fills.

 

[Mobjack Bay]

I think some of the discrepancy is a grams to ounces conversion issue. What I refer to as my 2 lb loaf mold holds a recipe made with 36 ounces oil. 1000 grams of oil = 35.27 ounces. The capacity of the mold is actually 53.4 ounces total batter.

edited for clarity

 

[DeeAnna]

"...1000 grams of oil = 35.27 ounces..."

The conversion of 1000 g fat to ounces (by weight) will be around 32 ounces. The specific gravity of most typical soaping fats is about 0.92 -- these fats are generally lighter than water.

edit -- I was thinking about this incorrectly and my advice is wrong. Mobjack Bay's numbers are correct as written. See posts 14 and 15 below for more.

 

[Mobjack Bay]

"...1000 grams of oil = 35.27 ounces..."

The conversion of 1000 g fat to ounces (by weight) will be around 32 ounces. The specific gravity of most typical soaping fats is about 0.92 -- these fats are generally lighter than water.

Thanks for the correction on the conversion. At least I know how much fat to use for my mold!

 

[MGM]

I found that 9oz oils fills to a good height on my tester molds (half-litre milk cartons) but beyond that I barely understand my molds. I once tried to do the math but it was way off so now I just eyeball (always knew you couldn't trust math!) and have my individual cavity mold nearby to catch any leftovers. A few months ago, I used my brand new slab mold for the first time and sorely underestimated, so i have these thin little bars. When I used that slab mold again last week, I made sure to make a big batch. It was way too much! I had to set aside about 1/4 of the batter because it traced too fast and I needed it very pourable, so I was worried i would end up with thin little bars again. Nope! Poured the 4 colours of batter at thin trace, then put my thick stuff in the cavity mold with a few swirls of leftover colours. So in addition to a full slab mold, i also had 8 or 9 bars, too! This is not the part of soap-making that's supposed to be mysterious....

 

[Mobjack Bay]

"...1000 grams of oil = 35.27 ounces..."

The conversion of 1000 g fat to ounces (by weight) will be around 32 ounces. The specific gravity of most typical soaping fats is about 0.92 -- these fats are generally lighter than water.

Well, actually, I’m confused. I’m converting from weight in ounces to weight in grams. Do I need to know the specific gravity to do that? Doesn’t 1000 g of anything weigh 35.274 ounces? I should have been clearer that I was using total batch weight from the soap calculator for my “mold capacity.”

 

[DeeAnna]

Oh dear -- I'm wrong. For some reason I was reading it as a conversion from volume to weight, and that is clearly incorrect. Thanks for pointing this out, @Mobjack Bay. I've edited my post to clarify that your numbers are right.

 

[Dahila]

my usual batch is 1400 g of oil my mold is good for 2200 g which it usually oil, water, additives. My hubby made the molds for this particular weight. My slab molds are made for 4000 g of oils. I think most people think about oils when they say about batches .
I had never had a batch that I had left over

 

[DeeAnna]

I think the reason why molds are often sized based on the weight of oils rather than the total batch weight is because the weight of oils is probably the most consistent ingredient from recipe to recipe. The weight of everything else -- water, fragrance, additives, even NaOH, can vary quite a bit depending on the soaper's preferences and the type of soap being made.

That's also why the 0.40 Rule (inches/ounces) or 0.70 Rule (centimeters/grams) aren't necessarily spot-on. They will get you close, but you have to tweak from there to fit how you make soap. A "more water" or "lots of bulky additives" soaper will need less batter than what these rules predict. A "less water" soaper will need more.

I typically use 1600 grams of fats per batch to fit my molds, but I might use more or less fragrance, different sorts of additives, and a bit less or a bit more water. I almost always end up with a little more soap batter than usual if I make a batch that's off the beaten track for me. So I know enough nowadays to get out my little "overflow" mold to take any extra batter.

 

[John Harris]

<--- totally baffled.

 

[Carly B]

It's a good question. I rely on Soapcalc. When you calculate, it will show you total weight of oils, but also, total weight of the uncured soap. So if your mold has six four-ounce cavities, you won't want more than 24 oz total. So just a little trial and error in the soapcalc should be all you need.

 

[TheGecko]

<--- totally baffled.

I'm with you brother. I thought I had it figured out, but now my head spinning.