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Lye to Fat Ratio Table
This table is for those of you who want to get a
bit more scientific in soap making, or just want to check and see if
the person who created the recipe you're planning on using knew what
they were doing. Each fat has its own saponification value, or "SAP
Value." And because of this, each fat requires a different amount of
lye to convert the fat to soap. (Jump to the bottom
of the page to learn more about this.)
For the soap to be made with no left over lye or
fat you must have very accurate measuring equipment. As the same oil
from different sources will have a slightly different saponification
value, we recommend you keep your soap a bit fat heavy to ensure you
don't end up with lye in your finished product.
In the table below use the 0-4% excess fat columns
(red) if you have accurate
technical equipment to test for excess fat or lye. Use the 5-8%
excess fat columns (green) to
make good hand/body soap and the 9-10% columns
(blue) if you want excessively fat heavy soap.
This page was written under close consultation by
Tina Howard at
Majestic Mountain Sage. In
fact, the following table was made using her
lye
calculator, which will automatically calculate the amount of lye
you need for a large variety of different fats. You plug into her
calculator the fats and quantities and it returns how much lye
you'll need.
| Calculate
the amount of lye you need by multiplying the amounts of
each fat (including superfatting oil) in your recipe by the
number intersected by the fat and your desired excess fat
column. Then add the different lye amounts for the different
fats in your recipe together.
Example: You want to calculate the amount of lye
for a recipe that calls for for 16 oz. of lard as it's only
fat. You want your finished soap to have 5% excess fat.
Intersecting the Lard row with the 5% column, you find the
number 0.132. Multiply 16 (fat wt) by 0.132 =
2.1 oz. of lye. |
Animal
Fat |
Desired Excess Fat In Finished Soap |
| 0% |
1% |
2% |
3% |
4% |
5% |
6% |
7% |
8% |
9% |
10% |
Goat Fat
Lanolin
Lard
Mutton Fat
Tallow |
0.138
0.075
0.139
0.138
0.140 |
0.137
0.074
0.137
0.137
0.139 |
0.136
0.073
0.136
0.136
0.138 |
0.134
0.073
0.135
0.134
0.136 |
0.133
0.072
0.133
0.133
0.135 |
0.131
0.071
0.132
0.131
0.133 |
0.130
0.070
0.130
0.130
0.132 |
0.129
0.070
0.129
0.129
0.131 |
0.127
0.069
0.128
0.127
0.129 |
0.126
0.068
0.126
0.126
0.128 |
0.125
0.067
0.125
0.125
0.126 |
Vegetable
Fat |
0% |
1% |
2% |
3% |
4% |
5% |
6% |
7% |
8% |
9% |
10% |
Canola Oil
Castor Oil
Coconut
Corn Oil
Cottonseed
Olive Oil
Palm Oil
Peanut Oil
Safflower
Soybean
Sunflower |
0.137
0.129
0.184
0.136
0.138
0.136
0.142
0.136
0.136
0.136
0.137 |
0.136
0.127
0.182
0.134
0.137
0.134
0.141
0.134
0.134
0.134
0.135 |
0.134
0.126
0.180
0.133
0.136
0.133
0.139
0.133
0.133
0.133
0.134 |
0.133
0.125
0.178
0.131
0.134
0.131
0.138
0.131
0.131
0.131
0.132 |
0.131
0.123
0.177
0.130
0.133
0.130
0.136
0.130
0.130
0.130
0.131 |
0.130
0.122
0.175
0.129
0.131
0.129
0.135
0.129
0.129
0.129
0.130 |
0.129
0.121
0.173
0.127
0.130
0.127
0.133
0.127
0.127
0.127
0.128 |
0.127
0.120
0.171
0.126
0.129
0.126
0.132
0.126
0.126
0.126
0.127 |
0.126
0.118
0.169
0.125
0.127
0.125
0.131
0.125
0.125
0.125
0.126 |
0.125
0.117
0.167
0.123
0.126
0.123
0.129
0.123
0.123
0.123
0.124 |
0.123
0.116
0.166
0.122
0.125
0.122
0.128
0.122
0.122
0.122
0.123 |
| Weight of water needed =
Total weight of fat in recipe times 0.38 |
Using potasium
hydroxide instead of Lye? Multiply the lye by 1.4 -
Using the example
at the top of the table, 1.4 X 2.1 oz (lye used) = 2.94 oz
of potasium hydroxide. |
|
Why
different oils have their own SAP values: It all has to do with the
length of the fatty acid chain. Briefly, it takes the same amount of
lye to saponify a short fatty acid molecule as it does to saponify a
long fatty acid molecule. The longer a fatty acid molecule is, the
more a set number of them weigh. Saying this in another way, the
longer chain fatty acids have a higher molecular weight. Hence, it
takes less lye to saponify the longer chain fats. You can determine
which fats above are the longer chain fats by looking at their SAP
values. The higher the SAP number, the shorter the chain. Most of
the fats above revolve around 18 carbon chain molecules with the sap
value hovering around .136-.140 in the 0% Excess Fat Column. (The
reason they are all slightly different is because the mixture of
different fatty acids in each fat or oil is slightly different.) On
the other hand, coconut oil contains about 47% lauric (C12), 19%
myristic (C14), 9.5% palmitic acid (C16) and 20-25% other residues.
Because coconut oil has several shorter string molecules, it takes
more lye to turn a given weight of them into soap. Coconut's SAP
value is .184. The reason for this is: the smaller the molecule, the
more you can fit into a given volume. The more you can fit in a
given volume, the more saponifiable bonds will be required and the
more base you will consume.
Speaking of a molar (equal number of molecules)
ratio, then it takes an equal level of base to saponify the fat/oil,
although the larger molecule will have a larger volume.
Thanks to Dr.
Richard Walton for many of the above comments.
Al Durtschi, E-mail:
mark@waltonfeed.com
All contents copyright (C) 1997-2000, Al Durtschi.
All rights reserved.
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