Koji Q+A
Akita Konno Answers your Koji Questions
Dr. Hiroshi Konno, president of Akita Konno, has been making the rounds of different breweries to share the success of his Roots 36 spores. I had the pleasure of meeting him at Islander Sake Brewery on the Big Island in Hawaii and we enjoyed a really exciting conversation about the technical aspects of growing koji.
Dr. Hiroshi Konno, President of Akita Konno
Introduction
Dr. Konno offered to answer any question we had, so we the Sake Discord if they had any burning questions regarding koji and this article contains the results.
It’s worth mentioning that Dr. Konno, is one of those rare individuals who is not just the 5th generation president of the 100 year old company his family started in 1930. He is an active member of the production team and will enthusiastically participate in a discussion on the chemical/molecular level. To add to that, not only can have a deep technical conversation, but will do so and in at least two differnt languages. Did you know he also speaks Dutch?
Some of the answers might require further tuning of our Q+A method, or a few back-and-forth questions to get the final details we want, but we figured it was best to share the information sooner than later.
Q1: What are the effects of high pressure rice steaming on Koji growth?
This answer was a little more high-level than we intended, but that is our fault for not being more specific. The details around pressure, superheated steam, and “dry steam” are something you can do plenty of research on, but suffice it to say, you are not going to be producing this without a very specific device. So when Dr. Konno talks about the “Second half” using “high-pressure dry steam”, just know that he’s referring to a process that requires equipment you probably will not have.
We’ll do a follow up on this topic and give you a much better understanding of how you can make this possible in your brewery. It’s unlikely that home brewers will be able to achieve this, but we believe in the power of your creativity.
For most of you, please ensure you are using “Dummy Mai”. This will markedly improve the steaming quality of your rice. If you’re a homebrewer, I put a little tutorial together for you here with Amazon links to the actual products. Commercial Brewers can purchase these in 5 gallon containers and there are velcro bags that you can fit them into in order to meet your needs for your koshiki.
The prerequisite for making high-quality koji is to prepare good steamed rice. Good steamed rice has a hard surface and a soft inside. Moist steam is not enough to make such steamed rice. This is because moist steam softens the surface.
There is a reason why steamed rice like this, which is hard on the outside and soft on the inside, is good. Steamed rice becomes sake only by melting it. If the surface of the steamed rice is sticky, the rice grains will stick to your hands or utensils, or the rice will stick together and form dumplings. Koji fungi first grows on the surface of the rice grains, so if the rice grains stick together and form clumps, the surface area for the growth of koji fungi becomes narrower. When making koji, it is very important that each grain of steamed rice is separated. Therefore, the surface of the rice grains should be hard enough that the rice grains do not stick to each other, and steamed rice that dissolves quickly in moromi mash.
There is an old-fashioned method called "hinerimochi" to check whether the steamed rice is hard on the outside and soft on the inside. Take a handful of steamed rice and stretch it out to check if it is elastic and if there are any hard parts left inside the steamed rice.
Therefore, in the second half of the steaming process, high-pressure dry steam is used. If high-pressure steam is suddenly ejected at normal pressure, it will become dry (pressure is 1 atm and temperature is over 100°C) and the steamed rice near the steam inlet will dry out. If you make koji using steamed rice that is dry on the outside and soft and elastic on the inside, it will become tsukihaze koji.
Broadly speaking, koji style can be divided into sohaze koji and tsukihaze koji. In sohaze koji, the koji fungi covers the entire rice grain sending many hyphae, or strands, growing into the kernel. In this style, the koji has strong enzymatic activity and the koji is rich in vitamins produced by the koji fungi.
Koji made according to the sohaze koji style dissolves the rice well and promotes strong fermentation, resulting in sake with plenty of body. It is used to produce full-bodied sake and regular sake to which alcohol is added.
In the tsukihaze koji style, the koji fungi grows in a spotted pattern over the rice grain. A cross section of the grain will show places where well-developed hyphae have grown into the grain and others where there are no hyphae. This still ensure appropriate enzymatic activity. but the vitamin and fatty acid content is lower. Sake made with this type of koji has a lighter taste than sohaze koji sake. Ginjo sake in particular, must be produced using the tsukihaze koji style. The Touji carefully controls the amount of koji fungi spores used, the quantity of water and the temperature to produce koji exhibiting these different characteristics.
I want to add a commentary here on something Dr. Konno says because he is referring to a very specific flavor profile and some additional information is needed to differentiate.
Tsukihaze is a style of koji that can lead to a lighter taste. We are not contesting that in any way.The effect of tsukihaze has changed over the years, from helping to eliminate off flavors in a pre-ginjo rice polishing era, to the most recent decade which saw a “ginjo boom” almost eradicate itself through over optimization on cleanliness and eliminating a lot of flavor in the process. An optimization that is currently self-correcting through sales and a preference for more “flavor”.
Dr. Chiaki Takahashi, Toji and Owner of Islander Sake, who is a former researcher at the NRIB and regular judge at sake competitions, mentioned that in recent years, almost 60% of daiginjo sake was made with sohaze koji. She explained that this is do to changing taste profiles. The industry is correcting to what “daiginjo” means.
So, if you are looking to create as “clean” and “light” a sake as you can, then futa koji is in your future and there are even spores that specialize for tsukihaze, but just be aware that you may be making a sake that largely is going out of style in Japan, and the taste profiles of Americans and Europeans might never have found pair well at all with their meals.
Q2: Effects of pH and minerals on Koji enzyme balance?
Note: Minerals are discussed in this section, but pH wasn’t as explicitly addressed. We’ll get another follow up question to them and see what data they have in this regard.
Water has a big impact on the quality of sake. Approximately 20% of the ingredients in sake are alcohol, amino acids, etc., but the remaining 80% is water. It is the opposite of wine, which does not use water, even though it is the same brewed alcoholic beverage. Water suitable for sake brewing is rich in minerals such as potassium, magnesium, and phosphorus, which are nutrients for koji fungi and yeast and promote fermentation. Approximately half of sake production is made in Nada (Kobe) and Fushimi (kyoto) in Japan. Nada sake is relatively hard and ferments easily, resulting in a strong aftertaste. On the other hand, Fushimi water is soft and ferments slowly, giving it a mellow taste. This is a unique characteristic brought about by the difference in hardness of the brewing water.
Note: I’m calling out usage of “brewing water” rather than just saying “water”. The previous few sentences give a more clear detail on the importance:
Water is often spoken of as imparting a “flavor”, and while that may be true at some levels of calcium, gypsum, or other salts with a strong savory, acidic, or even earthy flavor, the fact is, the majority of changes will be taking place in the fermentation.
The nutrients you provide your yeast will have a substantial change to the substances they produce. If you restrict certain minerals (or if they are absent), different points in the metabolism will malfunction. Depending on the strain, this will either cause a positive or negative effect.
In combination with this, there are other things like turbidity, ionization, flocculation, etc that can obviously have an effect. The most notorious is of course, is the concentration of iron above 0.02 ppm, which will create a discoloration in your sake due to chelating enzymes produced by koji.
Hardness is a numerical value that expresses the amount (mg/L) of calcium and magnesium contained in water, and water with a high content is called hard water. Water with little water is called soft water. Commercially available mineral water has a hardness of 30 to 40, but Nada water has a hardness of about 180, and Fushimi water has a hardness of about 40.
The water used to make sake must comply with standards applying to city water. City water contains more than 1 ppm of free chlorine as a hygiene measure. it does not matter for many use in brewery, but when it is used to adjust the sake quality, it should first be treated with activated charcoal or allowed to stand overnight to eliminate the chlorine. Furthermore, it must contain no more than 0.02 ppm of iron while the city water standard is 0.2 ppm. Too much iron gives sake a reddish-brown color and spoils and the aroma and taste.
As describe attached Table 1 show a comparison of the key point for brewery water and drinking water.
There was a paper on the effect of the mineral content of the soaking water used for making koji on the quality of koji, and I have attached a portion of it with English translations for your reference. See attached Fig1 to Fig5.
As can be seen from these results, adding minerals such as KH₂PO₄, Ca (H₂PO₄)₂, and KNO₃ to the soaking water makes it possible to produce well-balanced koji enzyme activity in a short time. Also, the fermentation of moromi mash made with these koji went smoothly. Additionally, adding 2mM of CaSO₄ or MgSO₄ to the preparation water will reduce the amino acid content from the early stage of fermentation. The sulfate ions dissolved in the brewing water are taken up by the yeast and have no negative effect on the flavor of sake. This is because sulfate ions accumulate as Clutathione, and the enzymes of koji fungi cannot break down Glutathione, resulting in a low amino acid content of final sake. See Fig 6 and Fig 7, Table 2.
Quick note on the addition of various salts like KH₂PO₄, NaCl, MgSO₄… we actually conducted a soak test with these added to the water and had a reverse osmosis control. The test group infact did absorb water more quickly, almost at a consistent 1% higher than the control (RO). This mean that for 10 minutes if the control was at 130%, the test with minerals added was at 131%.
More tests will need to be conducted to prove this, but we had read so many examples of this being the case, we wanted to see it for ourselves.
Q3: Is there a spore viability test for tane-koji?
Freshly made raw seed koji has a moisture content of nearly 28%. Its spores contain approximately 38% water- content. In order to maintain a high spore germination rate, raw seed koji must be dried and the moisture content must be kept below 15% for granular seed koji and 10% or less for powdered seed koji. In order to maintain a high germination rate of seed koji, it must be kept under dry conditions. The expiration date is 6 months after shipping if unopened. After opening, if you put a lot of clean desiccant into the Tupperware and seal it, it will be safe for up to one month. In that case, the germination rate may be reduced, so please use a large amount. As a general rule, please use it up once you open it. Seed koji is cultivated aseptically, so the inside of the bag is dry, but if you open the bag, it will absorb moisture from the outside and the germination rate will drop immediately, so be careful. See attached Fig 8 on 'Germination Rate'
Q4: What style of growing and hours are represented on the website?
Basically, it shows an example that follows the handmade koji style using a koji tray. The culture conditions and temperature rise pattern of the koji fungi vary depending on the type of seed koji, so be sure to contact the seed koji manufacturer to see the recommended temperature progression pattern before use, and then manage the temperature accordingly.
Note: This was not really what we were hoping for, but I think the best thing to do is decide which spores you are going to use, then email Akita Konno and ask for recommendations for a temperature progression pattern, koji-kin to rice ratio for moto, moromi, or general use. You should include the rice type, typical soaking amount (example: 133%), and taste of sake you intend to make (example: light and mellow, full-bodied/heavy and kara-kuchi).
Let us know if you need help. We understand that there can be challenges with communication.
Q5: What are the effects of hyphae length and growth speeds?
Regarding the length and shortness of the hyphae of koji fungi, long strains of koji fungi tend to have a relatively low amount of spores formation, while strains with short lengths tend to have a relatively large amount of spores formation. Also, when making koji from a strain with long hyphae, the hyphae become intertwined and the koji particles tend to form clumps. Once the koji block has formed into a lump, the temperature rises rapidly due to the heat of koji fungus's growth, so it is necessary to break it up to dissipate the heat. Particularly when making koji using large-scale koji production equipment, heat is dissipated by blowing air. If forced air is blown through the koji production equipment, cracks will form in the koji deposit layer, creating air passages and making it impossible to maintain uniform temperature control. The areas where the air is clumps become hot, and the areas where the wind passes through become cold. If the work is done in such a culture environment, the enzyme power will be extremely weak. Therefore, when selecting koji fungi, short lengths hyphae are often selected.
Seed koji is usually made from a single strain of koji fungi, but it is often made from a combination of several strain of koji fungi, in which case it is necessary to fully understand the characteristics of each strain. For example, if equal amounts of strains A and B are mixed, it is necessary to know in advance the temperature rise time (induction time = lag phase) during growth of the two strains. During the induction period, when koji fungi is inoculated and cultured for a certain period of time, it does not begin to proliferate immediately, but it takes time for it to grow at a certain rate. This period is called the induction period (= lag phase).
During this period, there is almost no increase in the number of koji fungi cells being cultured as it is a preparation period for growth. However, during the logarithmic growth phase, when metabolic activity is active and rapid growth follows, koji fungi grows most vigorously. During this period, koji fungi grow logarithmically.
When making koji, the first half of the cultivation period is called TOKO, and the second half is called TANA. The process of migrating from TOKO to TANA is called MORI. In koji making, the lag phase can be thought of as TOKO and the logarithmic growth phase as TANA.
For example, let's assume that the time to MORI (TOKO period) for strain A is 20 hours, and the induction time for strain B is 10 hours. When using a mixture of equal amounts of strain A and strain B, the induction time will not be the average of 15 hours for A and B. Only the characteristics of the B strain, which has a fast growth rate (short induction time), will always appear. Fast-growing strains become the dominant species because they grow faster. Therefore, when mixing multiple strains (seed koji), it is necessary to match the induction time (time required to reach MORI). Not only the growth rate of each strain, but also the physiological characteristics and enzyme balance of each strain will show only the characteristics of the fast-growing strain. Please see the example attached in Fig 9.
Q6: Would you consider sharing your detailed koji spore descriptions and growth data?
Of course, we will respond if you consult us. For this purpose, the important prerequisites are the points I mentioned in Q5.
Note: See my comment on: Question 5
Q7: What are your recommendations for spore count for hard rice vs soft rice?
Among the properties of raw rice, sake brewers are most interested in its solubility. This is because the temperature during the ripening stage of rice changes the composition and structure of starch, which greatly affects the solubility of rice. Even rice of the same variety can be hard in some years and soft in others. Also, the hardness and softness of rice differs depending on the variety of rice, so brewers are struggling with how to make koji for this year's sake brewing while accurately determining the condition of the rice.
Note: It really can’t be stressed enough actually. I’m working at Takeda Shuzo right now (2023-11-05 as I type) and all they talk about is how hard the rice is this year.
You might hear a lot about “our rice is grown at the same latitude and that makes it a good place to grow rice” or something to that degree. This is true obviously, but the ability to produce good rice requires a “sleeping” time. Yep, many living things have “down time”. Dr. Chiaki Takahashi (Islander Sake Brewery) taught me this.
For rice to produce a proper amylopectin structure (as Dr. Konno explains below), you need warm days and cool nights. As climate change continues to advance, the weather is becoming more and more difficult to farm and it does not stop there. These effects are making rice more brittle and creating more broken grains. The koji rice is therefore stickier because the starchy center is more easily exposed. Its a pain to work with. The soaking times are also different and more unpredictable due to cracks.
Keep an eye out as time progresses. I’m sure we’ll see many more studies around how to combat this issue.
When raw rice starch is heated in the presence of water, the starch absorbs water and swells, making it more susceptible to the action of enzymes. This is called starch gelatinization. When gelatinized starch is left at low temperatures, it crystallizes. This phenomenon is called starch retrogradation. Aged starch becomes less soluble in water and less susceptible to the action of enzymes.
Rice starch is composed of amylose and amylopectin. In non-glutinous rice, amylose: amylopectin = 20%: 80%. On the other hand, glutinous rice contains 100% amylopectin. Amylose is a linear molecule, while amylopectin is branched. Looking at the relationship between starch digestibility and molecular structure, the amylose content of raw rice and the side chain structure (branch length) of amylopectin have a strong relationship with the aging of steamed rice starch. In other words, the lower the amylose content, or the shorter the length of the amylopectin branches, the slower the starch retrogrades and the rice becomes less hard, so it tends to dissolve more easily.
In addition, when the temperature is high during the ripening stage of rice, the side chains of amylopectin become longer, causing the starch to deteriorate faster and become more difficult to digest. At low temperatures, the branches of amylopectin are short and the starch ages slowly, making it easier to dissolve. I have attached it to Fig10.
In this way, temperature changes during the ripening stage change the side chain structure of amylopectin, so you can easily see a difference in the disintegration properties of rice when soaked in an alkaline solution. In other words, if you add 1.7% KOH to raw rice and leave it at 30℃ for one day, the rice grown in extremely hot years will hardly thaw, while the rice grown in cooler years will gel at the outer periphery and grow larger. You can see it's collapsing.see Fig11.
In years when you need to make koji with such hard rice, try to significantly increase the amount of seed koji used to making koji with a large amount of koji fungi . As a result, sufficient enzyme activity is obtained. Also, change the preparation mix and increase the proportion of koji used by 2 to 3% from the usual 20% to increase the overall enzymatic power of the koji and allow the enzymes in the koji to break down hard rice. In the case of hard rice, it may be double steamed (steamed once and then watered again to increase the rice's water absorption rate, then steamed again). If it is still difficult to dissolve, enzymes for brewing may be used in combination with koji.
Q8: Which spores work better for using table rice?
Most of the rice used for sake brewing in the US is Calrose. We have previously conducted a small-scale test preparation using Calrose rice, so please refer to this. Even with Calrose rice, it is possible to make high-quality sake with 70% polishing. However, good results were not obtained with crushed Calrose rice. FK9 is already widely used by major Japanese sake brewers on the US West Coast.
In order to understand the starch structure of three types of rice (Calrose 70%) (Calrose 90% crushed rice) (Yamadanishiki 80%) with different rice polishing ratios, we added the above three types to an alkaline solution (0.1% NaoH). When above polishing rice or crushed rice was added, the solution of Calrose 90% crushed rice (B) instantly turned yellow, a phenomenon that occurs when brown rice contains a lot of protein. On the other hand, no such phenomenon was observed in Calrose 70% and Yamadanishiki 80%. See Fig 12.
Our members are going to send rice from Europe, mostly Carnaroli and Arborio, to have Akita Konno study it in further detail. The results should let us know which spores and other details are most beneficial, at least on an enzymatic level, but perhaps there are other aspects they will inform us on.
Conclusion
We did answer every question we wanted and there are plenty of points to clarify, even within these responses from Dr. Konno. What we do know is:
Need to ensure we have well steamed rice.
Need some minerals to ensure good enzyme balance and low amino acid production KH₂PO₄, Ca (H₂PO₄)₂, and KNO₃.
Keep your spores dry @ 15°C
Hyphae length is a descriptive trait of spores that lets you know the tendency to create a matt and you’ll need to adjust your mixing to release heat and moisture. Growth speed listed for spores is about mixing different strains and lets you know which one will probably take precedence due to its incubation time.
If you are working with hard rice, due to the increased long amylose chains in amylopectin, usemuch more seed koji and increase your recipe’s koji ratio by 2-3% (ex: 23% instead of 20%)
For those working with Table Rice, FK9 has seen to do well for large scale Japanese Brewers on the US west coast. (This includes the Sho Chiku Bai and others that basically liquify their kakemai (shikomi rice) by crushing it into a powder.). I would also throw out the option of using Roots 36.
Happy Brewing!
