Choosing Fragrance Oils for Cold Process Soap: Acceleration, Ricing and Discolouration Explained
Why some fragrances turn your batter to soap on a stick, why others brown, and how to read our test results before you commit to a full slab.
Cold process soap is unforgiving in a way that candles and perfume aren’t. You have a narrow window between adding fragrance and the batter setting, and if the fragrance decides to accelerate you don’t get that window back. The design you planned becomes a rescue operation.
The frustrating part is that you usually can’t tell from the description. A gentle floral can seize in thirty seconds. A heavy vanilla can behave perfectly. The scent gives you almost no information about how the oil will act at trace.
That’s why we test. We soap every fragrance we sell in the same recipe, record what happens, and publish the results — acceleration, discolouration, scent strength, and notes on what it was actually like to work with. This guide explains what those results mean and how to use them.
How much fragrance to use
5%, or the IFRA Category 9 maximum — whichever is lower.
Cold process soap falls under IFRA Category 9. Some of our fragrances are safe at 5% and above in soap; others are restricted well below it. The limit is set by the individual materials in the blend, so there’s no way to guess it from the scent or the family.
We publish the Category 9 maximum on every product page. Where it’s below 5%, that’s your rate.
A few fragrances have surprisingly low limits — Honey & Wildflowers is capped at 0.64%, for instance. It’s tempting to assume a fragrance that restricted will be too faint to bother with. In our testing it wasn’t: used at the maximum, the scent was still holding months later. Low usage rate doesn’t mean weak soap.
Calculating it
Fragrance percentage in cold process is calculated on your oil weight — the olive, coconut, palm, shea and any other oils and butters in your recipe. Not the water, not the lye, not the finished bar.
Fragrance (g) = total oil weight (g) × fragrance %
So for a batch with 1000g of oils at 5%:
1000 × 0.05 = 50g of fragrance oil
This is still the industry standard and it hasn’t changed. Every major soap supplier’s fragrance calculator works this way.
It’s also the method that lines up with IFRA. IFRA limits apply to the concentration in the finished product — and most of the water in your batch evaporates during cure, so the cured bar weighs close to your original oil weight. Calculating on oils gives you roughly the right concentration in the bar people actually use.
Calculating on total batch weight instead is the common beginner mistake, and it under-doses by around a third. If your soap smells like nothing, this is worth checking before you blame the fragrance.
The four things that can go wrong
Acceleration
The batter thickens far faster than it would unscented — sometimes within seconds. At its worst it’s what soapers call soap on a stick: the batter sets so quickly that pouring becomes plopping, and any design you’d planned is gone.
Acceleration is the single most common fragrance problem in cold process, and it’s the one most worth checking before you buy.
Florals and spices are the usual culprits. In our testing, Ylang Ylang, Suntan Lotion, Juicy Fruit Gum, Smoked Petals and Paradiso were all heavy accelerators. Jasmine Vanilla Almond was so fast it was almost unworkable — we’ve kept using it anyway, because the finished soap is worth the trouble.
But the rule is far from reliable, and that’s the point of testing. Bulgarian Rose — a floral, which by reputation should move fast — soaped beautifully with no acceleration at all. So did Aloe & White Lily. Meanwhile Lychee Guava Sorbet actually slowed trace, leaving more time for design work than an unscented batch.
If a fragrance accelerates, you can still use it. Soap at cooler temperatures, keep the design simple, and have your mould ready before you add the fragrance. A single-colour bar made with a fast fragrance is better than an intricate swirl you didn’t get to finish.
Ricing
The batter develops small hard lumps that look like grains of rice. It’s caused by the fragrance’s components separating out and solidifying rather than emulsifying into the oils.
Usually fixable — stick blending will smooth most ricing back out. Jade riced when first added and blended out easily; Sweet Pea Jasmine and White Lily & Rose did the same. Occasionally it comes alongside heavy acceleration, and then you have a harder problem, because the blending you need to fix the ricing is costing you the time you don’t have.
Seizing and separation
Seizing is acceleration’s extreme end — the batter solidifies almost instantly. Separation is the opposite: the fragrance pools out of the batter instead of incorporating.
Separation is usually recoverable with stick blending. Teak & Neroli separated slightly in our testing and blended back in without trouble.
Discolouration
The most predictable of the four, and the least harmful — it affects appearance only, never performance or scent.
Vanillin is the main cause. It’s the compound behind vanilla, caramel, bakery and many amber fragrances, and it oxidises to brown. The higher the content, the darker the result. We publish vanillin content on every product page, so this one you can check before you buy.
Vanilla goes very dark brown. So do Chocolate, Cloud, Tobacco Vanille and Cheirosa 59. That isn’t a defect — it’s the fragrance doing exactly what its composition says it will.
Other causes show up too. Some oils are naturally coloured and tint the batter the moment they go in. Citrus and spice materials oxidise and yellow over time. Banana Pudding turned yellow instantly on adding, then browned as expected.
Occasionally it’s spectacular rather than unwanted: Lust discolours to a bright red, which is not something you can achieve with most colourants.
Working with discolouration rather than against it usually gives the better result:
- Titanium dioxide can lighten the shift. Smoked Honey moves from brown toward beige with it. But it isn’t a cure — with Cloud, adding titanium dioxide produced a dark purple rather than white, and it was still heading brown.
- Choose colours that suit the destination. With Jam Doughnut, a red mica held red for nearly a year against the brown.
- Split the batter. For very dark fragrances, keep a portion unscented and colour that. Recommended for Baileys Kahlua and Smoked Coffee Whiskey.
If you want a white bar
Choosing a vanillin-free fragrance is only half of it. Your base oils set the starting colour, and no fragrance choice will overcome them.
Pomace olive oil and avocado oil both carry a strong natural colour and will produce a noticeably darker, greener or more golden bar before any fragrance is added. Unrefined oils and butters do the same. If a bright white bar is the goal, you need pale oils to begin with — or titanium dioxide to whiten the base.
So the recipe for white soap is all three together: pale base oils, a fragrance from our vanillin-free collection, and titanium dioxide if you want to push it further. Get the fragrance right and the base oils wrong, and you’ll still have a beige bar wondering why.
Scent retention: will it still smell in three months?
Cold process is a chemically hostile environment for fragrance. Some oils come through beautifully; others fade to almost nothing by the time the bar has cured.
There’s no way to predict this from the scent strength in the bottle. A fragrance that smells overpowering neat can be mild in soap, and vice versa. We record strength for every fragrance we test, and where we’ve gone back to a bar months later, we note that too — Tuscan Leather was subtle at first but holding well after nine months.
Bear in mind that scent can shift as well as fade. Smouldering Woods & Cinnamon faded noticeably after a week, then settled at a medium strength by four weeks. Baileys Kahlua cured to something we thought smelled faintly of playdough. Neither is a fault; it’s just what those materials do in a high-pH environment.
How to read our test results
Every fragrance we’ve tested is on the Cold Process Test Results page, with four columns:
| Column | What it tells you |
|---|---|
| Acceleration | How fast the batter thickened — from None through Mild, Moderate and Heavy |
| Discolouration | The final colour, described as specifically as we can |
| Strength | How well the scent held after curing |
| Notes | What it was actually like to work with, including ricing, separation and anything unexpected |
Our test recipe:
25% Coconut Oil · 25% Palm Oil · 35% Canola Oil · 10% Sweet Almond Oil · 5% Castor Oil 5% fragrance, or the IFRA Category 9 maximum
Read the notes column, not just the ratings. “Moderate” acceleration means different things depending on what you’re making, and the notes usually say whether a design was still possible.
An important caveat
These results come from our recipe, our method, and our workshop. Yours will differ.
A higher proportion of soft oils gives you more working time. Soaping temperature makes a substantial difference — several fragrances that accelerate for us are manageable if you soap cool. Even the weather plays a part.
We’ve seen this directly in the fragrances where our result and our customers’ don’t match. Fresh Cut Roses accelerated for some soapers and behaved for others. Mango Papaya was soap on a stick in our test, and completely fine for other people. Where we know results vary, we say so in the notes.
Make a small test batch before committing to a full slab. Especially with a fragrance flagged for acceleration, and especially if you’re planning an intricate design.
Choosing a fragrance for your first attempt
If you’re new to cold process, or new to us, start with something forgiving. From our testing, these were all easy to work with — no acceleration, no ricing, and good scent retention:
- Black Raspberry & Vanilla — a best seller, perfect pour, strong retention
- Blood Orange — beautiful to work with, great retention
- Coconut Lime — perfect pour, no discolouration, clean and fresh
- Apricot — soaps like a dream, no acceleration, no discolouration, strong scent
- Aloe & White Lily — a floral with none of the usual floral problems, scent holds well
- French Pear — a best seller, soaps very well, strong scent (discolours to tan brown)
- Chanel No 5 (type) — perfect pour, and the scent lasts a very long time (slight yellowing)
Once you know how your recipe behaves, the more difficult fragrances become manageable. Plenty of them are worth the effort.
What we publish, and where to find it
On every fragrance product page:
- Soap usage rate and IFRA Category 9 maximum — your compliance ceiling
- Vanillin content — your discolouration predictor
- CP soap test results — acceleration, discolouration, strength and notes
- Fragrance notes and family — top, middle and base
- Candle usage rate, IFRA Category 12 and flashpoint — if you make candles too
If you’re weighing up two fragrances and can’t decide, those numbers will usually tell you more than the description will.
Our cold process testing is done in-house by Kirsty, who holds an Advanced CP/HP Soap Certificate from the Handcrafted Soap & Cosmetic Guild and a diploma in cosmetic chemistry.
