Goat milk is an interesting addition to cold process soap. My first surprise was just how good it is.
Between milking, building the farm, normal farm chores, etc., I’m constantly washing my hands, and that’s tough on my skin. Winter is a bitch, especially when I’m milking in a lean-to of the barn, bare-handed in freezing cold. That’s in addition to feeding, washing buckets, etc. bare-handed in frozen, dry air. Even before farming, my hands would just get so dry the skin would crack, so I try to be careful about wearing gloves in cold, dry air. That’s not an option for some of my work now.
When I started making soap, I added about 25 hand washes to my day, some of them especially rough. Sometimes, my hands are in alkaline water, washing out soap-making equipment. If I spill “raw” soap, my hands get a splash of vinegar (ow). I thought my hands were going to be toast. But I’m also testing my soaps and using them – and my hands are in better shape now than they were early winter before farming (and I don’t have time for lotion now, so they should be worse!). I’m not using fancy soaps, just basic goat milk soap. The milk adds some nice fats, some lactic acid, potentially some nutrients. I guess that helps*.
Most advice I’ve gotten for soap recipes is to just substitute goat milk for water, and make the recipe as written. The flaw in that advice is that goat’s milk isn’t water (duh). It is water and fat (with added nutrients). If I just add goat milk, that extra fat is part of the recipe, even if I don’t account for it. I’m de-facto superfatting my soaps.
Sometimes that’s too rich, sometimes it’s just right. Saponified fats are stabilized in a form that can store well without risk of rancidity. Unsaponified fats – they’re susceptiple to decay. So I think it’s helpful to consider what the actual fat content is.
A side note – I make my soap by using the milk in the lye stage. I freeze it fresh so the butterfat is well-distributed in the milk, and use it partially thawed to keep the lye bath cold (otherwise the heat of the lye bath would overheat the milk). I believe that this process saponifies all the saponifiables in the milk from the outset. (Superfatting means putting more fats in the soap batch than the quantity of lye used can completely convert). I assume that the fats added earliest – when the lye is most potent – are more fully saponified. Butterfat has a short shelf-life (how long can you keep butter in the fridge?). So I want the butterfat saponified first.
Then I superfat by adding oils at light trace. Those oils are ones with longer shelf life, and I always hedge my bets by adding natural “preservatives” – something that resists rancidity (rosemary oleoresin, jojoba, meadowfoam oil, vitamin e) – to try to protect the unsaponified oils. If I don’t superfat as a separate step, I add rancidty-resistant additive to the batch of oils. I blend the oils one more time right before adding the lye.
Superfatting is a balance between making a rich, skin-friendly soap and making a long-lasting bar. We can’t predict what we’re doing if we don’t consider the total volume of oils in the recipe, including the milk fat. Most calculators don’t include milk as an option, and, if they did, they would be very imprecise because milk has a huge range of butterfat percentages.
What I do is estimate the butterfat as a percent of the milk weight. It’s the best approach I’ve found so far. This is an imprecise science. Lactation is dynamic – milk tends to contain more energy earlier in the day, more restful compounds later in the day; butterfat content varies with natural cycles ranging from time of day to point in lactation. I hold some milk back from soap making, so I look at it, taste it, estimate whether it’s changing. One of my goats is a breed that typically produces about 8% butterfat. The visual evidence of her milk seems to agree with that estimate (next year, I’ll do milk test and have the butterfat measured). So for a ballpak guesstimate, I use 8%.
So if my recipe calls for 40 oz of milk, that’s ~3.2 oz of butterfat (8%*40 oz.). If I’m using 80 oz of oils, butterfat is about 3.8% of my total oils/fats (80 oz oils +3.2 oz butterfat = ~83.2 oz oils). This may be part of why goat milk soap is so good – it’s just automatically superfatted by the simplistic advice that you just swap milk for water. It’s also some particularly awesome fat. But if you’re superfatting in the 0-5% range, having an extra 3.8% of oils that you didn’t plan for can really throw things off.
On the other hand, sometimes you want to be certain your superfat level is above a minimum. For the goat mentioned above, I calculate 5% butterfat; for another goat, I calculate 3% butterfat as the minimum.
I’ve seen lots of questions about this, so maybe my little nugget will help other goat soapers out there.
* There are a lot of claims that goat milk makes good soap because goat milk has a pH similar to human skin. That seems implausible. The lye used to saponify the oils has a very alkaline pH, and the final product has its own pH. To use an extreme example – If you mess up the recipe, you can get soap with a dangerously alkaline final pH (called lye-heavy, usually a result of accidentally omitting an oil) – even in a goat milk soap. Goat milk may alter the pH of the soap recipe in a beneficial way (perhaps), but it does not magically make a soap that has a perfect pH.