# Master Batch Lye - Quantities Help

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#### EllieMae

##### Well-Known Member
I'd like to start master batching my lye to save time for each batch. I understand most but I can't seem to figure out how you determine the quantity per batch when everything is already pre-mixed at my desired rate (33% in my case).

I've noticed that my water weight plus lye weight does not equal my lye water weight once combined. Is there a formula that I should be using to determine how much of the master batched lye water needs to be used per batch (based on weight of oils - I use the same recipe each time, only sometimes changing the overall weight to suit different molds). Or would this method require me to make each sized batch, weigh what the lye water weight is and record it for future use?

Or is it easier to master batch the lye water to 50/50, and then run the recipe through a calculator that accounts for master batching at 50/50, each time?

#### shunt2011

Staff member
Moderator
I master batch my lye 50/50. Then dispense the proper amount of lye per my recipe and add any additional liquid.

#### atiz

##### Well-Known Member
I'd like to start master batching my lye to save time for each batch. I understand most but I can't seem to figure out how you determine the quantity per batch when everything is already pre-mixed at my desired rate (33% in my case).

I've noticed that my water weight plus lye weight does not equal my lye water weight once combined. Is there a formula that I should be using to determine how much of the master batched lye water needs to be used per batch (based on weight of oils - I use the same recipe each time, only sometimes changing the overall weight to suit different molds). Or would this method require me to make each sized batch, weigh what the lye water weight is and record it for future use?

Or is it easier to master batch the lye water to 50/50, and then run the recipe through a calculator that accounts for master batching at 50/50, each time?
You don't have to do 50/50, you can masterbatch it 33% if that's what you always use. (I think people do 50/50 because it's easier then to replace the rest of the liquid with whatever.)

The weight of your solution should be the lye weight + water weight -- not sure what you mean when you say that "water weight plus lye weight does not equal my lye water weight once combined"! It really should equal it (chemistry was like a million years ago, but isn't there some law about conservation of mass or something...?).

If your masterbatch lye is 33%, that means that if you need X g lye for your recipe, you have to take 3X g of your solution (which will have Xg lye + 2Xg water). (If you need 50g lye, you would take 150g of the 33% masterbatch, and so on.)

Hope this helps!

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#### DeeAnna

##### Well-Known Member
If your total masterbatch weight is not the same as the original weights for the NaOH plus water, then I gather you've lost some water due to evaporation. If so, add that water back in to bring the weight back to what it should be. It should only be a few grams.

If you use lye at 33% lye concentration to make your soap and your masterbatch lye is at 33%, then Atiz's explanation is correct. An alternate way to get this same answer is to look at your recipe for the NaOH weight and water weight, and add the two numbers together --

Weight of masterbatch lye to use = NaOH weight + water weight​
Atiz's method and mine should give you the same answer -- just two ways of doing the same thing.

#### EllieMae

##### Well-Known Member
Okay, thanks guys. This is super helpful. I always assumed that it should equal up but when I actually weighed the lye water solution this past weekend it was off by like 20g. I then assumed that it does not add up (for some strange, chemistry reason I was unaware of)...but perhaps I was off in my calculations or weighing. My brain then started to hurt imagining that I'd have to use some silly equation each time I were to use master batched lye water.

Good to have the confirmation that water plus lye does, in fact, equal to the lye water weight. Makes life exponentially easier than I've been imagining since Sunday. Thank you!!!

#### DeeAnna

##### Well-Known Member
There can be some evaporation. Also there can be some rounding error.

If it's more than a few percent, I'd be concerned, but if the error is only a small amount compared to the total amount of solution you've made, a little discrepancy is pretty normal.

For example, I make 2000 grams of lye solution at a time, and being off by 20 grams wouldn't worry me. My goal is to have the weight be exactly right, but I'm realistic enough to know that's not going to happen.