The Science Behind Our Low Diacetyl Yeast

Why FRESH™ Is Better

You’ve heard that FRESH™ Chico makes cleaner tasting beer. Let’s unpack the science and the data. We’ll go over how diacetyl forms, why yeast's own cleanup and manufactured ALDC each fall short in some conditions, and how FRESH™ strains keep it in check in all conditions. We’ll finish up with an experiment that illustrates how FRESH™ Chico’s defense never wobbles, even when we throw the gnarliest risk factors at it.

Diacetyl control is complicated. Brewers are inventive, they have developed a variety of mitigation strategies. While diacetyl is often manageable using ordinary yeast’s abilities, you can also simply sidestep risks and constraints, surprises, extended timelines and effects on flavor, by using yeast that produces ALDC. With the fine-tuned genetics you get with FRESH™ strains, ALDC functions to prevent diacetyl in all conditions, not just some.

The Science

Diacetyl Forms

Yeast makes ɑ-acetolactate as part of its normal metabolism. ɑ-acetolactate, a precursor of branched-chain amino acid biosynthesis, is important for basic cellular functions. But, during fermentation, yeast makes more than it can use. With ordinary yeast, the excess leaks out of the cell. That is what becomes diacetyl in beer.

The conversion process of ɑ-acetolactate to diacetyl may be fast or slow, depending on wort and brewing conditions – driven by factors like higher temperature, lower pH, and higher oxidative potential.

Yeast is well able to take up diacetyl and break it down, but if that ɑ-acetolactate-to-diacetyl conversion is not efficient, yeast may not be available to clean it up, as when yeast begins to flocculate towards the end of fermentation.

Speeding Conversion

The diacetyl rest was named sometime around the midcentury, when brewing was becoming increasingly industrialized and temperatures could be precisely controlled. Allowing tank temperature to rise near the end of fermentation speeds up the chemical conversion of ɑ-acetolactate into diacetyl (and boosts yeast metabolism) so that yeast can eliminate diacetyl at a time yeast is still present and active enough to do so. And that does the trick – most of the time.

Enter Challengers (e.g., Hop Creep)

There are a number of scenarios where diacetyl is known to be persistent. A particularly prevalent one is during hop creep, where the dextrinases from hops break down the dextrins from your grist, into newly fermentable sugars. When hop creep kicks off, yeast — already on its way to the cone — spills out more ɑ-acetolactate just before it drops out. That leaves a pool of excess precursor that will become diacetyl unless the brewer intervenes. The correction costs time, effort, and money; but, worse, it’s also possible not to discover it until after packaging, when correcting it is no longer possible. Disaster.

The diacetyl spikes associated with hop creep have gotten more prevalent, especially with modern hopping techniques and increased hop loads; and also more intense with agricultural practices that influence hops’ enzyme content, like lower kilning temperatures.

The ALDC Solution (Spoiler Alert: The Format Matters)

ALDC can break down ɑ-acetolactate before it converts to diacetyl, which means brewers aren’t left to wonder whether a diacetyl rest will clean it up, or how long it will take. But the format makes a difference.

There are two ways to apply ALDC, either as a manufactured ingredient or via yeast that’s enabled to make it as an intracellular enzyme. One works sometimes, the other works always.

Manufactured ALDC

ALDC was first made available to brewers as a manufactured ingredient that’s purified from a separate microbial fermentation. The ALDC enzyme originally evolved to function inside a biological cell. This is in contrast to other common brewing enzymes like, say, amylases, which evolved to function outside of a cell. So, the fact that ALDC works at all in the wort/beer environment, where conditions are very different from the cellular environment, is pretty remarkable.

Manufacturers instruct brewers to apply ALDC at knockout, but it's not always effective that way, like during hop creep. To compensate – taking up experimentation themselves – brewers have begun additionally dosing at the time of dry hop, and sometimes even later. The new dose may manage some of the new ɑ-acetolactate that results, but we have seen in experiments how the enzyme may still fail to successfully hold diacetyl below 100 ppb (see “The Data” below).

100 ppb is the level at which most people begin to perceive diacetyl's buttery and slick character, but diacetyl has a negative effect on flavor well before it is recognizable as buttery; even at sub-threshold levels, it blunts the complexity of your hop profile. Decreasing diacetyl far below threshold, then, makes for a cleaner and better tasting beer.

Intracellular ALDC

Where manufactured ALDC can struggle, ALDC that is made by yeast and held within the yeast cell doesn’t. FRESH™ strains (like FRESH™ Chico and new Dry FRESH™ Chico), are enabled to produce ALDC intracellularly, which prevents diacetyl issues completely without exception. For two reasons:

Its functionality is protected inside the cell.
At the same time that the yeast produces ɑ-acetolactate, ALDC is ready to immediately break it down – before it can leak out of the cell.

But don’t just take our word for it, check out how it shows up in the experiment below.

The Data Shows...

After a hop creep-inducing dry hop, FRESH™ Chico is the only solution that reliably, comprehensively protects beer.

The Experiment

We brewed an IPA recipe with high dextrin wort, split it into four fermentors, and dry hopped each with hops we knew had high dextrinase activity. An ordinary American ale yeast throws off a lot of ɑ-acetolactate under those conditions. The goal of the experiment was to test three different methods of diacetyl control: Chico with intracellular ALDC (FRESH™ tech on board), a 3-day rest with the ordinary parent strain (no ALDC), and the ordinary parent strain in conjunction with manufactured ALDC dosed either at knockout or after dry hop.

After fermentation, we pulled samples. These samples were subjected to a forced diacetyl test (they were heated in order to convert all the ɑ-acetolactate to diacetyl) before analyzing them on our mass spectrometer. This gave us a read out for diacetyl potential, which is a good proxy for how much diacetyl could be present by the time a consumer has cracked open your beer.

Result 1: Both ALDC-assisted Fermentations Achieve Better Results Than Ordinary Yeast During Primary Fermentation

**Figure: Diacetyl potential after 5 days of fermentation.**

Starting from the left in the chart above, you can see that, under identical conditions:

Fermentations with FRESH™ Chico (teal bar) and fermentations with the parent ale yeast (light gray bar) both resulted in sub-threshold diacetyl levels (dotted line at 100 ppb). Note that FRESH™ Chico resulted in lower sub-threshold levels of diacetyl than the parent strain.
FRESH™ Chico (teal bar) and manufactured ALDC (slate bar) both kept diacetyl potential well below threshold. Note: This is true in primary fermentation; but that performance changes in the challenging conditions that are coming next…

Result 2: Only FRESH™ Chico (Intracellular ALDC) Works In Problematic Conditions

**Figure: Diacetyl potential after complete primary fermentation, 3 days after dry hop addition.**

Starting from the left above, you can see that, after an intentionally challenging dry hop:

FRESH™ Chico (teal bar) continued to protect beer thoroughly.
Fermentation with the ordinary parent strain (light gray bar) resulted in skyrocketing diacetyl.
Manufactured ALDC dosed at knock out (slate bar) was ineffective. Note: This may not come as a surprise — the reason brewers add an extra dose of manufactured ALDC at or after dry hop, is because it doesn't always work well when added at knockout.
ALDC added at the time of dry hop (blue-gray bar) was still not able to keep diacetyl potential below threshold. Note: This result was surprising. It showed that what brewers are doing to protect beer from a perceived weakness in manufactured ALDC isn’t a perfect solution.

What It Means

In conditions where yeast is highly prone to throwing ɑ-acetolactate late in fermentation, manufactured ALDC cannot fully protect beer from diacetyl. Not so for intracellular ALDC. After a hop creep-inducing dry hop, for example, FRESH™ Chico is the only solution able to protect beer — and still at the same ultra-low levels.

That means when FRESH™ Chico delivers ALDC, it never stumbles. First, because the ALDC enzyme is expressed inside the cell where it's always active. Next, because it's expressed in the right amounts, in the right place, at the right time.

Now, any time yeast is producing excess ɑ-acetolactate, it's also producing enough ALDC to intercept it, and all before it ever gets out of the cell. As a result, diacetyl is effectively, reliably, consistently banished to ultra-low levels, leading to a cleaner flavor profile and brighter hop expression, AND categorical protection from anything worse — with no exceptions. Bulletproof.