Brewing Non-Traditional Saké with Kveik

When I started my co-op at Escarpment Labs, I took a great deal of interest in koji. Known as Aspergillus oryzae, this filamentous fungi has a plethora of uses in food production, owing to the array of enzymes this organism produces. While taking a food science course at the University of Guelph, I learned about its use in the production of saké, which is a form of rice wine traditionally brewed in Japan. What was most interesting to me is that both koji and yeast are needed to create saké. Koji breaks down the starches in the rice by secreting amylase enzymes, which provides the yeast with sugars. The yeast then begins fermentation, turning the sugars into alcohol and other organic compounds.

Growing of koji in progress

As I got more comfortable with the yeasts we produce at Escarpment, I came across a particular family of yeasts known as Norwegian Kveik. The unique fermentation capabilities, including a large fermentation temperature range and high alcohol tolerance got some gears turning in my head. Additionally, Kveik are also known for producing lots of fruity esters, bringing lots of flavour to the table. I began thinking, what if I try brewing sake, but with Norwegian Kveik instead of traditional saké yeast?

I began by designing my experiment. After getting opinions from the staff on Kveik strains to test, I decided on three different Kveik strains: Årset, KRISPY, and Ebbegarden, a decision based on their individual fermentation characteristics and flavour profiles. As a control for the experiment, I used a traditional Sake yeast, strain K701, to compare the sensory attributes. With some much appreciated help from the Food Ferments team, we brewed one gallon of sake for each yeast strain we tested. The brewing process was quite involved, with daily stirring, testing of the specific gravity and pH weekly, as well as racking and pressing of the saké from the settled remains, known as kasu. As an aside, kasu is known for its uses in the kitchen as a marinade, but also has uses as a facial cleanser!

Fermentation temperature of saké is one of the more challenging aspects of production. A lower fermentation temperature will produce a cleaner end product, however the temperature must be high enough to allow the yeast to sufficiently ferment the saké. Most commercial saké breweries ferment around 10-15ºC.

Fast forward a few months, and the fermentation process has been completed, having the saké been bottled and aged for several weeks. Having waited patiently, it was finally time to test each trial! For the sensory evaluation, I had participants describe flavour profiles they noticed while tasting each sample, as well as asking them to rate each sample from most preferred to least preferred. This was a blind trial, so none of the participants knew which yeast was used in each saké. Participants included Escarpment Labs staff as well as trained saké tasters from That’s Life Saké + Wine (a saké and wine importer based out of Toronto).

As shown in the graph above, the Årset strain performed best in this trial, with tasters commonly noting cherry and orchard fruit flavours, while KRISPY, the second best performing strain, had tasting notes of citrus and otherwise clean, neutral profiles. Overall, the results indicate that Kveik yeast was preferred over saké yeast when used to ferment this style of saké. While saké yeast is the standard for traditional, high quality Japanese saké, this experiment shows that Kveik are more than capable of producing great tasting saké, especially in a homebrew setting.

For our Kveik ferments, we set our main ferment at 15°C. To achieve this, we placed a sous-vide in a water bath set in our walk-in fridge. If this is not an option for you, we recommend allowing it to ferment in the coldest room in your house, such as in a cellar or enclosed patio during the winter to get as close to 15°C as possible. If you are using a traditional saké yeast, a fermentation temperature of 10°C will provide you the best results. Traditionally in Japan, saké is fermented in the winter for this reason!

Note: the method used and listed here is not the traditional Japanese method of making saké. Typically, rice, water, and koji are added in three separate additions to the mash over a course of several days. This results in a product with an ABV of around 18-20%, due to the increasing amount of fermentable materials for the yeast to consume.

While unconventional, our method produced a saké which ended up with an ABV of around 14%, which is similar to commercially available saké. While making saké is hard work and is time consuming, the end result will leave you impressed with how two different microbes combined with simple ingredients can work together to create a delicious, refreshing fermented beverage.

About this Saké

This form of saké is unpasteurized, and is known as namazaké, meaning fresh saké. Namazaké tends to have fruitier flavour profiles, however only lasts about six months unopened when refrigerated. Alternatively, you can pasteurize your saké, which can be done by heating up a water bath using an immersion heater set to a high temperature and letting it sit for enough time to kill off any spoilage organisms. Typically, this is done twice; once before maturation, and once after bottling. This extends the shelf life of saké, allowing it to last from eight months to a year. Additionally, when unopened, it may be kept in a cool, dark space instead of a refrigerator. This type of saké tends to have more neutral flavour profiles when compared to namazaké.

Equipment

Note: To prevent contamination, all equipment directly involved with any ingredient should be sanitized using a food-safe sanitizer, such as Starsan, peracetic acid, or iodophor. We recommend doing the same to prevent any contaminants which may spoil your saké.

  • Large fermentation vessel (Must be able to fit 1 gallon of water, plus 3 pounds of rice and 1.25 pounds of koji rice, with excess room for foam)
  • Rice steamer
  • Colander
  • Long spoon or other mixing utensil
  • Food-safe sanitizer Hydrometer or other specific gravity measuring device
  • Juice press or Nylon brewing bag 
  • Mixing container
  • Somewhere to hold temperature, options highlighted above

Temperature Control Methods for home Saké fermentation

Water Bath

  • Sous-vide
  • Rubbermaid bin or bucket
  • Water (any tap water works here)
  • Large fridge or walk in cooler

Place the filled fermentation vessel within the container of choice, with the sous-vide mounted on the container. Fill the container with water, close to the maximum fill line on the sous-vide. Place this apparatus in the refrigerator, and plug in the sous-vide. Power the sous-vide on, and ensure that the water is able to circulate. Note that you may need to secure the fermentation vessel within the container, such as weighing it or tying it down, as it will float and may not rest in a stable position.

Chest Freezer

  • Temperature Controller
  • Chest Freezer
  • Container

Ingredients:

Makes 1 Gallon (5-6 750mL wine bottles) 

  • 1 packet of Escarpment Laboratories Kveik yeast (or any commercial Saké yeast)
  • 3 pounds of sushi rice (if possible, look for a higher polished saké rice, as it produces better quality saké)
  • Distilled water: 1 gallon for fermentation, 1 cup for nutrient mixture, and an additional 0.25 cups
  • 2 packets of Escarpment Laboratories Koji Rice or 1.25 lbs of fresh koji
  • Escarpment Laboratories Yeast Lightning: 2 grams
  • Lactic Acid: 0.5 teaspoon
  • Potassium Bicarbonate: 4 grams (Potassium chloride is preferred, however we had trouble sourcing some)
  • Magnesium sulfate/Epsom salts: One small pinch

Steps:

Rice preparation (2 hours) 

  1. Prepare rice by rinsing thoroughly until clear, around five times.
  2. Steep in water for one hour. After steeping, steam rice for an hour using a large steamer basket lined with cheesecloth or a steamer mat. The rice should be cooked through but still firm. While this takes place, continue on to the next step 3-6 (Rice can be soaked overnight, if necessary).
    NOTE: Steaming rice is essential as it results in the optimal consistency for digestion by the koji.
  3. Place 0.25 cups of water in the fridge to cool.

Rehydrate dry koji (5 minutes)

  1. Add 400g of Escarpment Labs Koji into a bowl.
  2. Slowly add around 120g - 160g of water, mixing well to rehydrate.
  3. Set aside the rehydrated koji.

Getting ready for first fermentation (30 minutes) 

  1. Mix 1 cup cold water and nutrient blend in a mixing container.
  2. Add yeast to nutrient mix from step 4, let sit 1 hour while rice soaks
  3. Add set aside rehydrated koji to mix from step 3 after 1 hour, allow mixture to sit 1 more hour while the rice steams
  4. After rice has been steamed, add 0.25 cups of refrigerated water and allow to cool so it is cold enough to work with. The rice will still be warm. Wait until the rice is room temperature before proceeding.
  5. Add this rice to your sanitized large fermentation vessel. Add to koji/yeast/nutrient mix from step 6 to fermentation vessel. Add the lactic acid. Mix gently for 2 minutes and cover, leave at room temperature, placing an airlock on top of the vessel if possible. 
  6. Mix twice a day for one to two minutes, ensuring to use a sanitized spoon.

After one week

  1. Place the fermentation vessel in an environment as close to 15ºC as possible. Stir for one minute, twice a day, using a sanitized spoon.
  2. Monitor specific gravity of the primary ferment for the levels to stop decreasing. We found ours to stop around 0.990 to 0.988, which took approximately 3 weeks. If you do not have a hydrometer, you can taste the ferment to see if you detect sweetness.
After three weeks
    1. Pour ferment into a cloth bag placed in a juice press, including leftover rice slurry. Press this rice, attempting to remove as much liquid as possible, allowing the liquid to drain into the large fermentation vessel that has been cleaned. This leftover rice product is known as Kasu and has myriad uses, such as a marinade, making amazake, or as a facial cream. Note that you can use a nylon brewing bag for this step if you do not have access to a juice press. 
    2. Move fermentation vessel with airlock to an environment as close to 10ºC as possible to allow the yeast to clarify and remove potential off-flavours. If this is not possible, refrigerate at 4ºC. Allow this to condition for one week, allowing it to sit without stirring.

After one week

  1. Bring fermentation vessel to an environment as close to 4ºC as possible to cold settle your saké, which helps the yeast settle to the bottom of the vessel.
  2. Siphon (or decant) and bottle your saké, taking caution to not disturb yeast at the bottom of the vessel. This will help create a clearer saké.
  3. Place bottles in the refrigerator and allow them to age for upwards of 3 weeks.
  4. Serve cold and enjoy!