Leucidal Liquid

Overview

Leucidal Liquid is the most popular of the “probiotic” or “natural” preservatives on the DIY market. It is made by fermenting radishes with Leuconostoc kimchii — the same bacteria responsible for fermenting kimchi. During fermentation, the bacteria produce a peptide (a small protein) called a bacteriocin, which has genuine antimicrobial activity. The radish liquid is filtered, stabilised, and bottled.

The appeal is obvious: a preservative made from kimchi-style fermentation, with an INCI that looks like a food ingredient rather than a chemical. For hobbyists building natural-positioning product lines, Leucidal is genuinely compelling on paper. It is paraben-free, formaldehyde-free, Ecocert-compatible, and very mild on skin.

But there is a serious caveat that every formulator needs to understand before using it. Independent challenge testing has consistently shown that Leucidal Liquid fails on its own in standard cosmetic challenge tests (USP 51, ISO 11930). It performs reasonably against bacteria but is weak on moulds and yeasts. Pairing it with a separate natural antifungal is the standard recommendation — which means you are paying for two preservatives instead of one and still getting “natural” rather than “robust.”

This entry exists so you know what you are agreeing to when you choose Leucidal. It is not a one-bottle solution. Treat it as a co-preservative.

What it does in a formula

Primary role: bacteriostatic protection in water-based natural formulations. The bacteriocin peptide interferes with bacterial cell membranes and gives reasonable protection against Gram-positive bacteria, with weaker activity against Gram-negatives and limited activity against yeasts and moulds.

Secondary role: minor humectant properties from the glycerol-rich ferment matrix.

How to use

Use at 2-4% of the total formula. This is a high use rate compared to synthetic preservatives — 20-40x more than Liquid Germall Plus on a percentage basis. Budget accordingly.

Add to the cool-down phase, below 40°C (the manufacturer specifies under 70°C, but the peptides are fragile and 40°C is safer). Heat damages the bacteriocin and destroys the preservative activity.

Works in pH 3-8, best below 6. Above pH 6 the peptide loses activity quickly.

Pair with an antifungal. This is not optional for any serious DIY product:

• A natural antifungal co-preservative made from coconut fermentation (the manufacturer-recommended natural pairing)
• Sorbic acid (the food preservative, used at 0.2-0.6%)
• Potassium sorbate (the salt form, more water-soluble)
• Or accept that the product is not broad-spectrum and label it as such.

Note: Leucidal is mildly cationic. It can complex with anionic thickeners (carbomers, xanthan gum can be borderline) and reduce both its own activity and the thickener’s. Test stability with your specific thickening system.

Best for / Worst for

Best for: small-batch, freshly-made, refrigerated products with short intended shelf lives. Also genuinely useful as a bacterial co-preservative alongside a separate antifungal. A reasonable choice for low-water-content products (lip balms with a tiny water phase, anhydrous products with botanical additions).

Worst for: products that will sit on a shelf for 6+ months. Mould-prone formulas with hydrosols, aloe juice, or fresh botanical extracts. Any product where a real broad-spectrum challenge test (USP 51) is going to be run as part of regulatory approval — Leucidal-only formulas fail.

Common pitfalls

Using Leucidal alone: the most consequential pitfall in this entire encyclopedia. There are countless DIY blog posts that recommend Leucidal as a complete preservative. Independent challenge testing consistently shows it does not protect water-based products on its own. If you sell or gift water-containing products preserved only with Leucidal, expect mould blooms within weeks. Always pair.

Not refrigerating: small-batch Leucidal-preserved products should be kept cold and used within 1-3 months. Treat them more like fresh food than commercial cosmetics.

Treating “natural” as “effective”: this is the broader pitfall. Natural-positioning preservatives have real trade-offs, and a product that grows mould is not safer than one preserved with phenoxyethanol. If a customer specifically asks for natural preservation, explain the shorter shelf life and recommend cold storage.

Anionic interactions: as noted, Leucidal can complex with anionic ingredients. If your product turns cloudy or thins out unexpectedly, this is a likely cause.

Ignoring the price: at 2-4% of the formula, Leucidal is much more expensive per batch than synthetic alternatives. Combined with the need for a separate antifungal, the preservation cost can easily be 10-20x what Liquid Germall Plus would cost.

Substitutes

• Geogard ECT — also Ecocert-certified, much stronger broad-spectrum coverage, works at 1% instead of 4%. The serious natural alternative.
• Cosgard (Geogard 221) — same family as Geogard ECT, no salicylic acid, also Ecocert.
• Leucidal SF / Leucidal SF Complete — newer ferment variants designed to address some of the spectrum gaps. Still benefit from a co-preservative.
• A natural coconut-fermented antifungal — the standard antifungal partner for Leucidal-style ferment systems. Use this with Leucidal, not instead of.
• Liquid Germall Plus — if “natural” is not actually required and you just need a preservative that works, this is the easiest answer.