How to calculate total batter weight to create 100 gram bars?

[bookworm]

Hi all you caring sharing peeps,

I'm trying to work backwards and figure out how much batter to pour into a mold to end up with bars that are approximately 100g after 6 week cure.

My current 1 inch bars after cure are approx 130g, the total weight of the batch per soap calc was 1539g , I cut the loaf into 10 bars and had a small end piece.

I've been looking at Marie Gale's article as posted on this forum:-

https://www.mariegale.com/calculating-net-weight-soap-part-2/
As per her calculation ,my water evaporation would be 19%. (oil weight 1050g; water weight is 294g & total batch is 1539g ; my recipe worked at 28% water as a % of oils)

I used soap calc & input total oil weight 900g , the total weight is 1306g and using Marie Gale's calculation, less 19% of water weight , the after cure weight would be approximately 105g.

I know some of you are math wizards; accountants and scientists and all have lots of wonderful skills.

Am I on the right track?

Thank you so much in advance.

 

[Marsi]

you have bars that cure out to 130g, and want bars that cure out to 100g

100g/130g is 76.9% (100/130x100)

reduce your recipe to 77% of the original

*edited to add
change the 28% water as percentage of oils to a lye strength percentage (30% to 33% is the current norm) - this will leave you with a better understanding of the relationship of lye to oil, and will give you a way of adjusting the water content of your soaps in a recipe independant way

 

[bookworm]

Wow you made it so easy. Thank you so much

 

[Marsi]

Wow you made it so easy. Thank you so much

just another enabler

welcome

 

[TheGecko]

I'm trying to work backwards and figure out how much batter to pour into a mold to end up with bars that are approximately 100g after 6 week cure.

I'm going to assume here that your reason for wanting to do this is so that you can sell 100 gram bars. The problem is, your soap doesn't stop curing at six weeks, it will continue to lose weight as time goes on so three months later, your soap will weigh less than 100 grams. I cut my bars at 5 oz and sell them as 4 oz.

 

[amd]

my recipe worked at 28% water as a % of oils

Agree with the sentiment expressed by Marsi to not use water as % of oils calculation. Water should be calculated based lye not the oils.

I would probably not use 19% water evaporation as a guideline for creating a correct sized batch, I'd be inclined to use a bit less - say 15% - as Gecko was meaning to say soap doesn't stop water evaporation at the end of the "cure" cycle (meaning the arbitrary number of weeks that we decide to leave our soaps sit before packaging). Water evaporation and cure are a continuous process that doesn't stop during the life of the soap. I also do as Gecko does - I calculate my bar size based on 15% water evaporation ensuring that my bar size isn't too small and likely to fall under my intended goal, and then understate the label.

 

[DeeAnna]

I wouldn't try to shave the weight too close for all the reasons others have shared.

Another issue to keep in mind -- If you make soap in a loaf mold and cut the loaf into bars, you will invariably have small variations in height and thickness. These variations can materially affect the weight.

For my bars, if I change the cutter thickness by a mere 1/32" / 0.8 mm, that will change the weight of a bar by around 3%.

I also have found the bars at the ends of the loaf often weigh a smidge less than bars cut from the center of the loaf. Unless you pour at a very thin trace, some "crowning" of the soap in a loaf mold will be hard to prevent..

I list the net weight as 4.5 ounces (130 grams) on the label for the bars I sell. I require all salable bars to weigh no less than 140 grams and preferably more like 145-150 grams at the time of packaging.

I will remove the occasional older bar from the shop if I see one that is looking shop-worn. That's usually after some months in the shop. I've found these bars weigh close to 130 grams, so they clearly continue to lose weight.

 

[Zany_in_CO]

Math challenged here!

I go at it from a different angle. I know that 30 oz. of fats (X a factor of 1.37) will produce 41 oz. of soap (approx.). My loaf mold holds 40 oz. I smooth the top and use the excess to make a small sample.

With a few exceptions, for most batches I use the default settings on SoapCalc, i.e., 38% water as % of Oils and 5% superfat. Works for me. Never had DOS.

This makes 8 bars, cut at 1", weighing more or less 5 oz. because it's so difficult to get perfect cuts. I label them 4.5 oz, using the lowest bar-weight after cure.

If I want "perfect" bars, I'll cut only 7 bars and trim them to 5 oz after cure and rebatch the scraps into 1.5 oz. round samples.

NOTE: This comes from making the same formula, batch after batch, year after year, for wholesale customers. You get to a point where you can finagle the outcome of whatever soap you're making.

 

[bookworm]

Thank you all so much, it's been a very educating experience. I'm going to start implementing your great and clearly very experienced advices and see how it goes.

 

[TheGecko]

And something else that I just thought of (jeez I'm an *****) that can affect the Net Weight of your soap is planning and beveling. I just checked a half dozen bars that I made last year and everyone single one of them weighs less than 4oz. Fortunately, all my 'sales' this past year have been private sales to friends and family and I don't package my wholesale account.

 

[lucycat]

Another thought. When you reduce the recipe size to get to the 100g bar you will be changing the height of the bar if using the same mold. Do you want to do that? Would it be better to increase your recipe size and cut 11 bars from the log with the bars having less width but the bar being taller. Both will look different than your current bar and probably one will have better visual appeal, or it may make you decide you like your 130g bar the best..

 

[bookworm]

Thank you once again for all the so helpful tips. I'll be meeting with my friend who requested this size bars & run all the options through with her.