What Is ALDC Enzyme in Brewing? Prevent Diacetyl Before It Starts

If you have ever tasted a beer that came across as buttery, butterscotch-like, slick, oily, or like movie-theater popcorn, you have probably run into diacetyl. In small amounts, diacetyl can be stylistically acceptable in a few traditional beer styles. In most modern brewing, especially clean lagers, pilsners, blonde ales, Kölsch-style beers, West Coast IPAs, hazy IPAs, and other dry-hopped beers, diacetyl is usually considered an off-flavor.

That is where ALDC enzyme comes in.

ALDC, short for alpha-acetolactate decarboxylase, is a brewing enzyme used to help prevent diacetyl formation during fermentation. It works by converting alpha-acetolactate, the main precursor to diacetyl, into acetoin before that precursor has a chance to oxidize into diacetyl.

In plain English: ALDC helps stop buttery beer before it starts.

It is especially useful for brewers making lagers, quick-turnaround beers, heavily dry-hopped beers, and any beer where a clean finish matters.

If you already know you need it, you can find our ALDC product here: ALDC Enzyme from SoCal Brewing Supply. If you want to understand how it works, when to use it, and what it can and cannot do, keep reading.

What Is Diacetyl?

Diacetyl is a vicinal diketone, often abbreviated as VDK, that gives beer a buttery, butterscotch, movie-popcorn, or slick mouthfeel character. White Labs describes diacetyl as having a very low flavor threshold, roughly 50–150 ppb, while Brew Your Own notes a threshold around 0.1 ppm in light beer. Either way, the important point is that it does not take much diacetyl for a beer to taste noticeably buttery.

Diacetyl can come from several sources, including fermentation management issues and contamination, but normal yeast metabolism is the main pathway brewers are usually managing.

During fermentation, yeast produce amino acids. One of those amino acids is valine. While yeast are making valine, they produce an intermediate compound called alpha-acetolactate. Some alpha-acetolactate leaks out of the yeast cell into the beer. Once it is outside the cell, it can chemically oxidize into diacetyl.

Healthy yeast can later reabsorb diacetyl and reduce it into less flavor-active compounds, mainly acetoin and eventually 2,3-butanediol. That cleanup phase is why brewers use a diacetyl rest: keep the beer warm enough and yeast-active enough for cleanup before cold crashing or packaging.

The issue is that diacetyl cleanup takes time — and the precursor can remain hidden even when the beer tastes clean.

What Does ALDC Do?

ALDC changes the pathway before diacetyl forms.

Instead of allowing alpha-acetolactate to oxidize into diacetyl, ALDC enzymatically converts alpha-acetolactate directly into acetoin. Acetoin is much less flavor-active than diacetyl, so the beer avoids the main buttery off-flavor pathway.

A simplified version looks like this:

Without ALDC:

Alpha-acetolactate → diacetyl → yeast cleanup → acetoin / 2,3-butanediol

With ALDC:

Alpha-acetolactate → acetoin

That is the key concept: ALDC works on the precursor, not on finished diacetyl.

This is why ALDC is best used early in fermentation or at a known risk point like dry hopping. It is a prevention tool, not a rescue treatment for beer that is already buttery.

Does ALDC Remove Diacetyl That Is Already in Beer?

No. This is one of the most important practical points.

ALDC does not remove free diacetyl that has already formed. White Labs states this clearly for Brewzyme-D: it works on alpha-acetolactate, the diacetyl precursor, and does not reduce diacetyl already present in beer.

If beer already has diacetyl, you still need yeast to reduce it. That usually means warming the beer, keeping yeast in contact, allowing more time, and making sure fermentation health is not the underlying problem. If the diacetyl is coming from contamination, ALDC will not fix that either.

Think of ALDC as a seatbelt, not a body shop. It helps prevent the crash. It does not repair the damage afterward.

When Should Brewers Use ALDC?

ALDC can be used in many beer styles, but it is especially useful in the situations below.

1. Lagers and Cold Fermentations

Lagers are one of the classic use cases for ALDC. Diacetyl reduction is slower at cold temperatures, and many lager fermentations require a warm diacetyl rest near the end of fermentation.

ALDC can help reduce the amount of diacetyl precursor available to become diacetyl, which may shorten maturation time and reduce the need for an extended diacetyl rest. White Labs notes that Brewzyme-D can reduce lager maturation time by up to two weeks, depending on process and beer.

This does not mean every lager should be rushed. Good yeast health, proper pitching rate, oxygenation, temperature control, and sensory checks still matter. But ALDC gives lager brewers a useful layer of protection.

2. Heavily Dry-Hopped Beers

Modern dry-hopped beers are another major use case.

Dry hopping can contribute to hop creep, a phenomenon where enzymes from hops break longer dextrins into fermentable sugars. If yeast are still present, those new sugars can trigger a slow secondary fermentation. The Brewers Association technical brief on hop creep notes that the consequences can include changes in alcohol, CO2, and diacetyl.

ALDC does not stop hop creep itself. It does not prevent hop enzymes from creating fermentable sugars. What it can do is help reduce the diacetyl risk created when renewed yeast activity produces more alpha-acetolactate.

That is why ALDC is commonly used at yeast pitch and sometimes again at dry hop for heavily dry-hopped IPAs.

3. Fast-Turnaround Beers

If you are trying to package beer faster, diacetyl potential becomes one of the biggest risks. A beer may taste clean at the moment you check it, but still contain alpha-acetolactate that can later convert into diacetyl.

ALDC helps lower that risk by reducing precursor before it becomes a problem. This can be especially useful for breweries trying to increase tank efficiency, but homebrewers benefit too: fewer “it tasted fine before kegging” surprises.

4. Beers Made With High-Diacetyl-Risk Yeast or Process Conditions

Some yeast strains produce more diacetyl than others. Highly flocculent strains may also drop out before cleanup is complete. Fermentation stress can make the issue worse.

ALDC is useful when you are dealing with:

• Lager yeast at cold fermentation temperatures
• Highly flocculent ale strains
• Heavy dry-hop loads
• Short turnaround schedules
• Beers that will be cold crashed quickly
• Fermentations where yeast health or oxygenation may not be perfect
• High-gravity beers that place extra stress on yeast

It is not a substitute for good fermentation, but it can reduce the downside when the process is demanding.

How to Use ALDC Enzyme

For most brewers, the simplest method is:

Add ALDC to cooled wort at the start of fermentation, around yeast pitching.

Good mixing matters. Enzymes are not yeast. They do not reproduce and spread through the fermenter the same way yeast cells do. The enzyme has to contact its substrate to work effectively. White Labs emphasizes dosing Brewzyme-D into the fermenter before knockout or in a way that ensures thorough homogenization.

For homebrewers, that means adding it to the fermenter around pitching time and gently ensuring it is distributed in the wort.

For dry-hopped beers, a second dose at dry hopping can be useful if the product directions support it. This is especially relevant for hazy IPAs, heavily dry-hopped pale ales, and other beers where hop creep could create renewed diacetyl potential.

ALDC Dosage for Homebrewing

Dosage depends on the exact product and concentration, so always follow the product label.

For the ALDC enzyme sold by SoCal Brewing Supply, the listed dosage is:

Use 1/4 teaspoon per 5 gallons of wort at the start of fermentation.

Some dropper-style ALDC products list dosage as one dropper full per 5 gallons. White Labs Brewzyme-D lists a homebrew dosage of 10 mL per 20 L / 5 gallons, and a pro dosage of 15–20 mL per hL.

Those numbers are not interchangeable across every brand because product concentration and packaging differ. The practical rule is simple: use the dosage listed for the ALDC product you have.

For dry-hopped beers, especially beers with large dry-hop loads or previous hop-creep issues, consider dosing at pitch and again at dry hop when directed by the manufacturer.

Ready to use ALDC in your next batch?

SoCal Brewing Supply carries CellarScience ALDC Enzyme for brewers who want a cleaner fermentation profile and lower diacetyl risk in lagers, dry-hopped beers, and quick-turnaround batches.

Shop ALDC Enzyme for Brewing →

Best Timing for ALDC

The best timing is usually early fermentation.

Add ALDC:

• To cooled wort
• Around yeast pitching
• Before or during transfer into the fermenter if you can mix thoroughly
• Again at dry hop for hop-creep-prone beers, if product directions support it

Avoid thinking of ALDC as a late-stage fix. It is much more useful before diacetyl forms than after the beer has already developed buttery flavor.

Temperature and pH Range

White Labs lists Brewzyme-D activity at:

• pH: 4.0–7.0
• Temperature: 50–104°F / 10–40°C

That range covers normal fermentation conditions, but warmer active fermentation is generally a better time to use ALDC than very cold finished beer.

Dry-hopped beers can be trickier because beer pH is lower after fermentation, and dry hopping can shift pH. White Labs notes that pH management matters in dry-hopped beers: low pH can inhibit enzyme performance, but pH that rises too high creates other compliance and stability concerns. For most homebrewers, the practical takeaway is to use ALDC at the recommended time and avoid treating it as a last-minute addition to cold, finished beer.

Does ALDC Replace a Diacetyl Rest?

Sometimes it can reduce or eliminate the need for a traditional diacetyl rest, but that does not mean every brewer should ignore diacetyl testing or fermentation management.

White Labs states that, with proper dosing, a diacetyl rest is not required for Brewzyme-D. In practice, the safest wording is this:

ALDC can reduce the need for a long diacetyl rest by preventing much of the precursor from becoming diacetyl.

If you are packaging beer commercially, brewing a delicate lager, or pushing turnaround time, a forced diacetyl test is still smart. The test helps reveal whether hidden alpha-acetolactate remains by forcing it to convert into diacetyl before packaging.

For homebrewers, this can be as simple as warming a small beer sample and comparing aroma against an unwarmed control sample. It is not as precise as lab testing, but it can catch obvious precursor problems.

ALDC and Hop Creep

Hop creep deserves special attention because it is one of the reasons ALDC has become more popular with modern brewers.

The Brewers Association describes hop creep as the result of hop enzymes modifying beer during dry hopping by breaking long-chain dextrins into fermentable sugars. If live yeast remain in suspension, those new sugars can lead to renewed fermentation.

That renewed fermentation can cause:

• Lower final gravity than expected
• Increased alcohol
• Increased CO2
• Package overpressure risk if it happens after packaging
• New diacetyl potential

ALDC helps with the diacetyl side of that problem. It does not stop the enzymatic creation of fermentable sugars. It does not replace stable gravity checks. It does not remove the need to understand yeast activity during dry hopping.

But it is very useful as an insurance policy against the diacetyl spike that can follow hop creep.

Benefits of ALDC

Cleaner Flavor

The most obvious benefit is reducing buttery, butterscotch, and slick diacetyl character in beers where that flavor does not belong.

Faster Maturation

Because ALDC prevents much of the precursor from becoming diacetyl, brewers may spend less time waiting for yeast to clean up diacetyl after it forms.

Better Lager Turnaround

Lagers often need more time because cold fermentation slows cleanup. ALDC can help brewers produce cleaner lagers with less maturation delay.

More Confidence in Dry-Hopped Beers

Dry-hopped beers can be unpredictable because hop creep depends on hop variety, crop year, contact time, yeast in suspension, and beer composition. ALDC helps reduce one of the biggest flavor risks from that process.

Better Process Consistency

Even when your process is good, diacetyl risk can change from batch to batch. ALDC helps create a more consistent pathway away from diacetyl formation.

Better Tank Efficiency for Commercial Brewers

For breweries, faster maturation can mean better tank utilization. Novonesis, White Labs, and other enzyme suppliers position ALDC products partly around faster throughput and reduced warm maturation time.

What ALDC Does Not Do

ALDC is useful, but it has limits.

ALDC does not:

• Remove diacetyl that has already formed
• Fix contamination
• Replace sanitation
• Stop hop creep from creating fermentable sugars
• Replace stable gravity checks
• Replace yeast health, oxygenation, or proper pitching rates
• Guarantee literal zero diacetyl
• Make every beer ready instantly

White Labs notes that diacetyl will rarely be zero due to enzyme kinetics, but proper use should keep it far below flavor and aroma thresholds.

That is a good standard: ALDC is about risk reduction and process control, not magic.

How ALDC Fits Into Good Fermentation Practice

The best results come when ALDC is used alongside good brewing fundamentals:

• Pitch enough healthy yeast
• Oxygenate wort appropriately for the yeast and gravity
• Control fermentation temperature
• Avoid crashing too early
• Keep yeast in contact long enough for cleanup
• Use a forced diacetyl test when packaging timing matters
• Monitor dry-hopped beers for gravity stability
• Package only when fermentation is truly complete

ALDC makes a good process more reliable. It should not be used to justify a sloppy process.

Who Should Use ALDC?

ALDC is worth considering if you brew:

• Lagers
• Pilsners
• Helles
• Cold IPA
• West Coast IPA
• Hazy IPA
• Dry-hopped pale ales
• Blonde ales
• Kölsch-style beers
• Cream ales
• High-gravity beers
• Fast-turnaround beers
• Any beer where buttery character would be a flaw

It is also useful if you have had recurring issues with diacetyl, especially after dry hopping or after packaging.

Practical Homebrew Example

For a 5-gallon batch, a typical use case would look like this:

1. Brew as normal.
2. Chill wort to fermentation temperature.
3. Transfer to the fermenter.
4. Add ALDC at the product’s recommended dosage — for our ALDC product, 1/4 tsp per 5 gallons.
5. Pitch yeast.
6. Ferment normally.
7. For heavily dry-hopped beers, consider a second dose at dry hop if the product directions support it.
8. Confirm fermentation is complete before packaging.
9. Use a forced diacetyl test if you are trying to package quickly or if the beer is especially diacetyl-sensitive.

Should You Still Do a Forced Diacetyl Test?

If the beer matters, yes.

A forced diacetyl test is still one of the best practical checks for hidden precursor. The basic idea is to heat a beer sample, which accelerates conversion of remaining alpha-acetolactate into diacetyl, then compare it to an unheated sample.

If the heated sample smells buttery and the control does not, the beer may still have diacetyl potential.

ALDC reduces the risk, but testing gives you confidence.

Final Takeaway

ALDC is one of the most useful modern fermentation tools for brewers who care about clean beer and predictable turnaround.

It works by converting alpha-acetolactate, the main diacetyl precursor, directly into acetoin. That prevents the precursor from following the normal path into diacetyl, reducing buttery off-flavor risk and shortening the time brewers spend waiting for cleanup.

Use it early, mix it well, follow the product dosage, and remember what it is: a prevention tool. It will not fix contamination, remove existing diacetyl, or replace good fermentation practice.

But when used correctly, ALDC can make a real difference — especially in lagers, fast-turnaround beers, and dry-hopped beers where hop creep can create renewed diacetyl risk.

If you want to add ALDC to your next batch, you can order it here: ALDC Enzyme | CellarScience | Prevent Diacetyl.

Technical References

This guide was built from manufacturer and brewing-education references including White Labs Brewzyme-D technical materials, Brewers Association hop-creep education, Brew Your Own diacetyl brewing science, and current ALDC product usage guidance.