Lather test

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Apr 19, 2019
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Last summer I developed five different soap recipes to test the idea that soaps with the same properties in the soap c@lculator (and similar fatty acid profiles, see below) will lather the same regardless of the sources of the fats. For each recipe, I started with a different palmitic and/or stearic-rich hard fat or hard fat combination. From there I added varying amounts of coconut, rice bran, high oleic sunflower and castor oils to all of the recipes and then added avocado oil as needed to match the FAs as closely as possible among recipes.

All recipes have the following properties in the SMF c@lculator:
Bubbly 17
Cleansing 13
Conditioning 52-53
Hardness 41-42
Longevity 29
Creamy Lather 33-34

And this fatty acid profile:
Lauric + Myristic 13
Palmitic + Stearic 29 (all palmitic dominant, but ratio varies among recipes from p:s 1.1 to 2.2)
Ricinoleic 5
Oleic 40-42
Linoleic + Linolenic 8-9

The palmitic and stearic-rich fats or fat combinations and palmitic:stearic ratios:
palm (no stir) + shea (refined); p:s = 2.2
lard (Armour brand); p:s = 2.2
tallow (Soaper’s Choice); p:s = 1.6
GW 415 soy wax + cocoa butter (unrefined); p:s = 1.2
cocoa butter (unrefined) + shea (refined); p:s = 1.1

Every recipe was made with aloe juice as a partial water replacement, sodium citrate as a chelator, Nurture’s 8th and Ocean FO and 2% superfat. The lye was food grade from Essential Depot. The soaps were color coded by adding different color swirls. (ETA: the soaps were made 8-11 August 2021; the testers identified the soaps by color; all testers knew there were five base fats/combos and the makers were given the FA profile and soap properties)

I sent the soap to 16 testers, including 10 “soap lovers” and 6 “soap makers.” Each tester was asked to score the soaps from 1-10, with 10 being the highest, based on the amount of lather components (creamy, foamy, bubbly; which I did not define in advance) and the total amount of lather. After watching a few soap lovers test soap in the past, I decided to keep it simple and did not give explicit directions on how to do the testing. I also asked for information on water hardness (soft, softened, hard) and for any comments on the soap. I asked the soap lovers to let me know which soap(s) they liked the best. The soap makers also voluntarily shared their preferences. A couple of the soap makers went over and above the call of duty by varying the way the soap was physically manipulated during testing, looking at how the lather changed over time of use (i.e. a few seconds to 20 seconds) and by comparing lather at the sink versus in the shower. My partner and I also tested the soap repeatedly over the last few months, but I excluded our results from the analyses to avoid any bias.

By mid-December, 13 testers had returned results, including 9 “soap lovers” and 4 “soap makers.” The testing period spanned from mid-October to mid-December.

Lather results - The most obvious feature in the results is high variability among testers for most lather attributes regardless of the recipe. Individual testers had preferences (see below) but compelling trends in performance across lather components or total lather amount were lacking due to high variability among testers. I used box and whisker plots (Excel) to summarize the lathering results by recipe:


The bubbly attribute is possibly the most interesting, with the palm & shea soap at the low end and the soy wax & cocoa butter and cocoa butter & shea soaps holding their own. A few testers that liked the latter two soaps specifically commented on how bubbly they were. For the record, I didn’t bother to make graphs of the scoring for lather across time or by water type (hard, softened, soft) because I didn’t notice any trends.

Preference results* - Eleven Nine testers provided 1st and 2nd favorite soaps and two four additional testers provided a first preference. Eight of 13 testers (61%) ranked the cocoa butter + shea soap in the top two (4 as first, 3 as second, 1 as tied). The lard and soy wax + cocoa butter soaps were next, with lard getting four (4) 1st place votes, but no and one (1) 2nd place vote and soy wax + cocoa butter getting two (2) 1st place votes, two (2) 2nd place votes, and one (1) vote as tied for top two. Tallow had two (2) 1st place votes and the palm + shea soap came in last with two (2) 2nd place votes. Testers generally had nice things to say about the soaps (lovely, awesome, ”love the soft, creamy lather”). Despite the low cleansing number, one tester thought some of the soaps left their hands feeling squeaky clean.

What’s the best way to test soap? An email exchange with another maker after they sent me their results led us to realize just how much the physical manipulation of soap during use affects the amount and quality of lather produced. For my soaps, we both found that rolling the soap in one or two hands makes bigger bubbles compared with rubbing the soap between palms. Perhaps this is due to more air being introduced when a soap is rolled. Without adding more water, both methods produce creamier lather as time goes on. When I test in the shower, the soap is wetter and so am I. Then I started noticing that I tend to use the rubbing method when I’m testing small bars of soap at the sink, but in the shower I roll bigger bars using two hands. When I was watching my partner lather up, I noticed that her rubbing method produced creamy results in 5-10 seconds, while my rubbing produced larger bubbles and denser “foamy” bubbles over the same amount of time for the same soap. A couple of testing runs I did with my eyes closed convinced me that my initial assessment of a soap is heavily influenced by seeing how it lathers. I’ve also tried testing soap with gloves on, which robs me of the sensation the soap produces in my hands. Testing soap qualities is full of complexities!

ETA: a few other variables that I discussed with soap makers during lather testing were: effects of size and shape of bar (surface area effects?), changes in lathering after a new bar is used a few times and effects of water temperature (warm water dissolves soap faster than cold water)

Final notes! The fatty acid profile I’m using for GW 415 is the “best fit” profile I calculated a couple of years ago based on the available data from the manufacturer. I guess it could be off slightly, but we’ll never know unless someone else decides to take a deep dive into the numbers. I added the avocado oil to raise the palmitic without having to make the cocoa butter percentage cost prohibitive. I briefly considered trying to tease out the unsaponifiable component of the recipes, but gave up on that idea pretty quickly because the data available online vary tremendously. At the least, unsaponifiables and “hidden fatty acids” that are not shown in the c@lculators add unknowns for those who want to formulate on the basis of fatty acid profiles.

*argh… this section didn’t seem quite right to me. I double checked the testing sheets and corrected the numbers. (9 testers x 2 votes = 18, 4 testers x 1 vote = 4, 18 + 4 = 22 votes total). I also missed a 2nd place vote for lard.
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For my soaps, we both found that rolling the soap in one or two hands makes bigger bubbles compared with rubbing the soap between palms.
That sounded a bit esoteric, I promptly had to test it by myself, and what shall I say, it works! It was about time for a rather young soap on the high-oleic side. I rubbed it like I usually do → hardly any lather, creaming the hands with opaque slime. The bar set aside and water added, I got a decent lather out of it, but that's an extra step.
When rolling, though, it instantly exploded under fluffy lather! (And solving the oleic slime drama as a pleasant side effect.)

This clearly needs further investigation. It might well be that you/your testers just have converted me from a “rubber” to a “roller” soap bar user personality 😵😃.
An email exchange with another maker after they sent me their results led us to realize just how much the physical manipulation of soap during use affects the amount and quality of lather produced.

There is that too. I use a foo-foo (aka bath puff) in the shower/bath. At the sinks (bathroom/kitchen), I use cavity soaps or the trimmings I have rolled into a ball.

I now feel I should ask my testers how they 'wash' with my soap, but given some of their 'sense of humors', best I don't. LOL
When I test soap, I roll and rub to see how much a difference there it.

You did a great job with the test and crunching all the info.
I just wish we knee what makes the recipes behave differently when the FA profiles and numbers are so similar.
Roller here too!
My grandma is a rubber though... I have noticed, and I know for sure I've commented on it somewhere here, that how you make your lather is a factor. When she uses the same soap, I make more lather.

Staying tuned for more!

And yey for butter soaps lol
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Here’s a way to test soap at the sink that’s about as standardized as it can be for home testing. For the greater good, I watched this video multiple time with the sound on 😂. The bars are: castile (bar 1), “very, very different soap” (bar 2, starts 2:57), tallow (bar 3, starts 4:20) and shampoo bars (bar 4, starts 5:28; bar 5, starts 6:30). Despite the shift in technique from rolling to rubbing, it looks promising.

@Mobjack Bay was so foolish kind to send me the raw data of her wonderful survey, for some further data mining.

Here is how the correlation matrix over the set of parameters looks like:
(positive values: If X is higher rated, Y is as well, negative values: If X is higher rated, Y is lower rated)
Though the water hardness (bottom row/left column) works very unscientific behind the scenes, the survey statistically reproduces the old wisdom that soaps works better in soft water than hard water (negative correlation hard-total).

To little surprise, most testers agreed to the connection “more bubbly = more better” (R=+0.48). On the other hand, the bubbliest soaps were perceived considerably less “creamy”.

The soaps that scored best at “bubbly” were those with P/S close to 1; none of the high-palmitic (P/S=2) soaps performed as well. Thanks to @Mobjack Bay's effort of balancing the FA numbers, we see that this effect is only significant for the “bubbly”, but not for the “creamy” and “foamy” parameters, which (on average) don't care at all about P/S.

Let's have a closer look into the data. The bubbly rating vs. total score, but this time resolved by individual testers and their water hardness:
There is a trend that most (but not all) testers follow (diagonal point cloud from bottom left to top right). However, a few very bubbly soaps were rated mediocre overall, and some not so bubbly were someone's favourites.

However, as great as these data are, it'll be difficult to improve the statistical significance much further by brute-forcing (more testers, more recipes, more soaps), unless the evaluation process isn't standardised as a such. And statistical noise (curing speeds, personal preferences, lather technique, water temperature, etc…) come on top of all this. 😵

Fun with statistics!
resolvable = capable of having the reason for or cause of determined, as in "I have no doubt that this mystery will turn out to be resolvable if only @ResolvableOwl will take a look." ;)

Just over half of the points that fall off the main diagonal point cloud, the ones marked with asterisks, tag to three professed lovers of creamy soap. The four "outlier" purple circles are from a single individual (tester #2). Interestingly, two of these individuals account for the two 2nd place rankings of palm soap among the top favorites.

ETA: almost forgot this. Here’s how tester #2 scored the soaps:
lard: total = 10, creamy = 10, foamy = 4, bubbly = 2
tallow: total = 10, creamy = 9, foamy = 5, bubbly = 3
palm_shea: total = 7, creamy = 6, foamy = 8, bubbly = 4
soy_cocoa: total = 5, creamy = 3, foamy = 7, bubbly = 9
cocoa_shea: total = 5, creamy = 3, foamy = 3, bubbly =10
They liked the lard best and the palm + shea second best even though they rated the tallow soap second with respect to creaminess.

I'm now in the midst of trying to develop a more standardized way to test the qualities of these soaps without a lot of handwashing. Will post when I have actual results.
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This is very cool! It's amazing how people wash their hands differently and never discuss it 🤣

Personally I would start with a fairly vigorous back-and-forth motion (rubbing, I guess) and then progress to rolling if I don't get a decent amount of bubbles pretty sharpish. I remember reading a thread where someone was describing how they lather tested their soap, and iirc they were talking about a certain number of 'strokes', which I felt at the time of reading might not be doing justice to the soap; I can't help wondering now if they were a rubber and unaware of the rolling technique!

I'm also fascinated by the stats above, although I'm not a statistician myself I can appreciate a good graph or two. I get the impression that the hard water people are fairly evenly distributed along the bubbly scale, but the softer ones are more towards the bubbly end. Makes sense, but I'm itching now for a follow up experiment/survey to find out if the hard water people also (by necessity) use the rolling technique to draw out the bubbles and are therefore getting a more granular view of the bubblability (I'm sure that's a word)...
resolvable = capable of having the reason for or cause of determined, as in "I have no doubt that this mystery will turn out to be resolvable if only @ResolvableOwl will take a look." ;)
Oh, if you only knew the anticlimaticly banal back-story of that username! 🤭😂

how they lather tested their soap, and iirc they were talking about a certain number of 'strokes', which I felt at the time of reading might not be doing justice to the soap
Surface structure! Using a crinkle cutter might be cheating already. I have noticed it several times with my beloved pierced-cube silicone mould that it makes quite a lathering difference if I rub its smooth or indented side over my palm.

bubblability (I'm sure that's a word)
Bla blubb billy tea … my spell checker is crazing out, but I have learned to take the recommendations of spell checkers with a grain of salt.

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