Author: Jordan Folks
Crisp, refreshing, and designed for ultimate drinkability, International Pale Lager typically leans on a simple grist of Pilsner malt and adjuncts like corn or rice, the latter being a key ingredient in popular Japanese examples like Asahi and Sapporo. As craft brewers continue to push boundaries, there’s been growing interest in relying on more traditional ingredients when making this style of beer, with one notable option being koji.
Technically, koji is the solid-state culture produced when Aspergillus oryzae spores inoculate a grain substrate. While a mixture of soybeans and wheat is used to create the koji for soy sauce, rice koji is the quintessential component in sake. Recently, some adventurous brewers have been swapping regular rice for koji rice to elevate flavor complexity and improve starch conversion, as the mold provides its own amylase enzymes while also reducing the mash pH. Moreover, research suggests kojic acid can inhibit oxidation, potentially extending shelf life and preventing the “stale” notes that often plague light lagers.
It’s no secret that I love pale lager, and while I tend to lean into classic German and Czech version, I’ve got zero qualms with a deliciously dry International Pale Lager, especially as an accompaniment to tasty Japanese food. I also enjoy trying new ingredients in my brewing, which is what led me to picking up some koji rice – would it really have a perceptible impact, and if so, would I like it? Curious to see for myself, I designed an xBmt to test it out.
| PURPOSE |
To evaluate the differences between an International Pale Lager made with 10% koji rice and one made with only Pilsner malt.
| METHODS |
Wanting to keep the variable in as much focus as possible, I went with an International Pale Lager recipe consisting of 90% Pilsner malt and 10% koji rice for one batch, while the other had the koji rice replaced with additional Pilsner malt. Thanks to F.H. Steinbart for providing me with the malt for this batch!
Koi Pond
Recipe Details
| Batch Size | Boil Time | IBU | SRM | Est. OG | Est. FG | ABV |
|---|---|---|---|---|---|---|
| 5.3 gal | 60 min | 19 | 5.1 SRM | 1.042 | 1.013 | 3.81 % |
| Actuals | 1.042 | 1.013 | 3.81 % | |||
Fermentables
| Name | Amount | % |
|---|---|---|
| ISARIA 1924 | 9 lbs | 90 |
| Koji Rice OR additional ISARIA 1924 | 1 lbs | 10 |
Hops
| Name | Amount | Time | Use | Form | Alpha % |
|---|---|---|---|---|---|
| Hallertauer Mittelfrueh | 71 g | 60 min | Boil | Pellet | 2.3 |
| Hallertauer Mittelfrueh | 28 g | 10 min | Boil | Pellet | 2.3 |
| Saphir | 28 g | 10 min | Aroma | Pellet | 2.3 |
Yeast
| Name | Lab | Attenuation | Temperature |
|---|---|---|---|
| Kanpai (L55) | Imperial Yeast | 77% | 46°F - 55.9°F |
Notes
| Water Profile: Ca 50 | Mg 4 | Na 10 | SO4 66 | Cl 35 |
Download
| Download this recipe's BeerXML file |
The day before brewing, I made a starter using two pouches of Imperial Yeast L55 Kanpai.
After collecting the full volume of water for two 5 gallon/19 liter batches, adjusting each to the same mineral profile, and heating them up, I incorporated the grains and set the controllers to maintain the same 95°F/35°C for a brief acid rest. I did this because that’s apparently the maximum temperature at which the koji enzymes are active. I then raised the mashes to 147°F/64°C.
During the mash rests, I weighed out the kettle hop additions.
At the completion of the mash rests, I took pH readings showing a pretty vast difference between the worts.
After removing the grains, the worts were boiled for 60 minutes with hops added at the times listed in the recipe. Once finished, I quickly chilled the worts before taking refractometer readings showing a slight difference in OG.
I also took another set of pH readings.
After transferring identical volumes of wort from either batch to sanitized fermentation kegs, I evenly split the yeast starter between the batches then placed the fermenters in my chamber controlled to 48°F/9°C. With signs of activity absent 11 days later, I took hydrometer measurements showing an interesting difference in FG.
I also took a final pH reading of the fermented beers.
At this point, I cold crashed the beers overnight then transferred them under pressure to CO2 purged serving kegs that were placed on gas in my keezer. After 5 weeks of cold conditioning, they were carbonated, clear, and ready for evaluation.
| RESULTS |
A total of 19 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of beer made with 10% koji rice and 2 samples of the beer made with only Pilsner malt in different colored opaque cups then asked to identify the unique sample. While 10 tasters (p<0.05) would have had to accurately identify the unique sample to reach statistical significance, only 8 did (p=0.28), indicating participants in this xBmt were unable to reliably distinguish an International Pale Lager made with 10% koji rice from one consisting of only Pilsner malt.
My Impressions: Out of the 5 semi-blind triangle tests I attempted, I correctly identified the odd-beer-out every time. To my palate, the beer made with koji rice had a sharper character that was similar to a German Pils, while I perceived a hint of butter in the version made with only Pilsner malt. As such, my preference was for the beer made with koji rice.
| DISCUSSION |
Rice has been used as a beer ingredient for centuries, and even longer when looking at fermented beverages in general. However, the use of koji rice in beer is a relatively novel concept that was spearheaded by modern craft brewers looking to create unique flavor profiles. Interestingly, tasters in this xBmt were unable to reliably distinguish an International Pale Lager made with 10% koji rice from one consisting of only Pilsner malt.
The fact the beer made with koji rice had a lower mash pH, higher OG, and higher FG indicates the koji rice had an objective impact, though based on the triangle test results, any effect on aroma, flavor, or mouthfeel was minimal enough to be imperceptible by most tasters. It’s possible this would have been different had a higher proportion of koji rice been used, though that may also have led to other issues considering the acidity it contributed.
While I preferred the beer made with koji rice, the truth of the matter is that nearly every beer I brew relies solely on barley malt, and that’s not going to change. However, I look forward to experimenting with koji rice more in the future, likely using less than I did in this xBmt in order to hit a more ideal mash pH.
If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!
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4 thoughts on “exBEERiment | Impact 10% Koji Rice Has On An International Pale Lager”
Was the rice cooked/flaked before the mash or just uncooked koji rice into the mash?
I’m unfamiliar with this ingredient.
Based on the introduction, I would have thought the comparison would have been Koji Rice vs. Regular Rice in a Rice Lager.
Then there were some other confounding steps:
1. Denaturing the Koji enzymes so quickly after activation. It can take a few days for Koji to work its magic. (see Sake procedures)
2. Choosing such a low percentage of Koji which is right at the flavor/aroma detection threshold. (no surprise folks couldn’t tell the difference)
3. Not adjusting mash pH on the control, which was way too high, even at pre-boil. (resulting in under-conversion, the Koji version was practically spot-on OG & FG.)
I appreciate the effort, but the choices here baffle me. (seems to be a recurring theme of this site)
A member of our club made his first brew as a Sake. That’s quite a bit of work, and as noted above, the Koji need 2–3 days in a happy temp range to convert the rice starches to sugar. (in this case, they’d convert barley sugars)
Another member, who makes rice lagers (with 30% adjuncts) decided to toss some Koji in a batch, but did it during fermentation so as not to denature the enzymes. This did make it near impossible to determine gravity impact, as the Koji were doing conversion while the yeast were eating, but it certainly added flavor.
I do hope you can manage to keep some of both beers around 3+ months to see if there is indeed an Oxygen-scavenging effect, but I know that is a tall order!
Really interesting experiment! From my experience with white koji, it can drop mash pH as much as—or even more than—acidulated malt. If you use more than ~5% at mash-in, the pH can easily slip below the optimal range (5.2–5.5), which may inhibit amylase activity and lead to a higher-than-expected FG. This seems particularly relevant here given your low pH readings.
When using higher percentages of koji, I recommend a “staged addition”: add only a portion at mash-in, and the rest later once conversion is already underway. If you’re worried about conversion time for that late addition, a great workaround is to pre-saccharify it (like making Amazake). Just mix the koji with 3x its weight in 60°C (140°F) water and hold it in a thermos or sanitary container for a few hours—or overnight—before adding it to the main boil or mash.
I’m currently at the MoreBeer booth at CBC promoting koji applications. If anyone wants to geek out on the practical use of white koji, come by and say hi!