Ditching Diastaticus

Saisons are known for being nuanced with distinctive dryness and delicate fruit, hay, and spiced notes. However, the cross-contamination risks associated with using diastatic saison yeast—including exploding cans or a knock on your door from the TTB for over-shooting your targeted ABV — are anything but subtle. 

Some brewers have chosen not to brew saisons so they can avoid introducing a diastatic strain into their brewery, but saisons are delicious. As ardent members of Team Saison, we would like to encourage all brewers to brew more of them. To that end, let’s go through two different approaches for safely brewing saison and saison-style beers without using diastatic yeast: 

You can create a highly fermentable wort and use a non-diastatic brewing strain, and other ingredients, to mimic the aromas of saison — or you can use a saison yeast strain that’s been made non-diastatic.

Saisons can be light or dark, rustic or refined, but their common thread is their dryness. This low final gravity is the result of fermenting with diastatic yeast strains. The descriptor ​“diastatic” means that the yeast make a protein called ​“diastase”, which is another name for ​“amylase”. Amylases are enzymes that catalyze the conversion of starches into sugars. Diastatic yeast express a version of amylase called glucoamylase that can break down long-chain sugars like dextrins into glucose.

What this means practically is that when other brewing yeast quit, diastatic saison yeast keep going. Most brewing strains are capable of fermenting the simple sugars glucose, fructose, sucrose and maltose. And some have the ability to utilize the trisaccharide maltotriose. In addition to these smallish sugars, wort also contains longer polymers of glucose, known as dextrins, which cannot be metabolized by non-diastatic brewing strains. These residual long-chain sugars contribute to a full mouthfeel and are reflected in your final gravity. In saisons, however, the glucoamylase produced by diastatic yeast breaks these long-chain sugars into glucose, allowing the yeast to ferment more of the sugars in the wort and resulting in a lower final gravity and a drier finish.

The Risk

Diastatic yeast becomes a problem when this glucoamylase activity is unleashed in the wrong beer. When a beer fermented with non-diastatic yeast gets cross-contaminated with diastatic yeast, glucoamylase from the diastatic yeast leaves the cells, catalyzes the breakdown of residual dextrins into glucose, and provides fermentable sugars not only for itself, but also for all of the remaining yeast cells that are in the beer. This additional fermentation results in a lower final gravity than intended, increased ABV, and increased CO₂.

Avoiding It

Of course this cross-contamination is just from yeast, and your brewery is built to grow and nourish — and then ultimately get rid of — yeast, so using a diastatic yeast strain in your facility is manageable with diligent SOPs. If knowing all that, if you would just prefer not to take the risk, there are two approaches to making saison-style beer without using diastatic yeast.

The key to brewing a saison without using typical saison strains is to target the high attenuation rate and lightly phenolic, delicately spicy aroma that saisons are known for.

Creating Highly Fermentable Wort 

To compensate for not having a yeast-derived diastatic enzyme around, we need to manipulate the brewing process to create a highly fermentable wort by other means. 

Three approaches to optimizing attenuation are to: mash at a low temperature, use an exogenous amylase and add dextrose during the boil. Targeting a mash temperature of around 148°F provides favorable conditions for beta-amylase activity. Malt-derived beta-amylase attacks starch chains from their ends and cleaves off molecules of highly fermentable maltose, resulting in a highly fermentable wort. Exogenous amylase enzymes, such as amyloglucosidase, which can convert both straight and branched long-chain sugars into fermentable simple sugars, are also available to aid in breaking down starch and are generally best used in the mash. Finally, replacing some of your grist bill with dextrose will shift the ratio of sugars in your wort towards more simple sugars and will result in a drier finished beer.

Approaching Aroma

To help build the aromas associated with saisons without using saison yeast, start with a lightly phenolic, non-diastatic Belgian strain with strong attenuation potential. Omega Yeast’s ​“Belgian Ale A” is a great option with its balance of delicate fruit and spicy pepper notes combined with an attenuation that can approach 85%. 

Small-batch trials can also be used to discover your favorite aroma and performance profile. One approach is to pull off neutral wort from the big brewhouse into a few carboys and pitch different strains for comparison. Alternatively, if you have a distinctive grain bill in mind, a pilot brew split into those growlers you have in a case in the corner of the brewery, for example, can give you enough information to find the strain that represents ​“saison” to you. 

Elements of Style

Leaning on the other ingredients in your recipe will help bring a strong association to the style. Consider pulling a more farmhouse-rustic flavor from alternative grain types like rye or spelt, which add earthy-spicy notes. Paying homage to farmhouse style can also include using local malt and hops and even foraging for herbs, spices, and other ingredients that grow in your area. For hops, low alpha acid varieties work best since too much bitterness can throw off the balance that this delicate style requires. Styrian Golden or Saaz can provide the more traditional herbal and earthy take on a saison. More modern approaches could lean into lemon and citrus varieties like Citra, Amarillo or even Sorachi Ace. A small dry hop can help to drive that extra 0.5 – 1 Plato of attenuation you are targeting, too. 

Last, but not least, don’t be timid with carbonation: target a sharp 2.7 – 3.0 vol of CO₂ to leave the kind of refreshing finish that you need for this highly drinkable style.

Diastatic yeast’s flavor and aroma profiles are not connected to their diastatic trait. They exist together in saison strains, but don’t rely on each other biologically. Does that mean we could have a saison strain with all of its same, sought after flavor and aroma that’s just not diastatic? Yes! The R&D team at Omega Yeast has been working to perfect just such a thing through a genetic engineering approach.

Stay tuned for more of the science behind how Omega Yeast designs non-diastatic saison strains, coming soon.