Why is Kimoto?
“The Yeast Starter Formerly Known As Kimoto”
There are plenty of articles out there that tell you what kimoto is and how it’s made, but as we so often do, we’d like to tell you WHY “ki”moto is “生”酛. Let’s start with the basics to give some context and then dive deep into the nature of the symbiotic organisms that make this so incredible.
Kimoto Basics…
Kimoto is a type of yeast “starter”. A yeast starter is like a cradle of life. We aim to create a safe environment and give our preferred organism a head start before sending it out into the main mash to work a 18 hours a day in the alcohol factory.
One of my mentors, who is one of the most knowledgeable people in the fermentation industry, as well as a prolific member of the Sake Brewers Guild, Reade Huddleston, once said that our goal with beer and wine fermentation is to cultivate yeast, but in sake fermentation our goal is to condition yeast.
Cultivating yeast.
Conditioning yeast.
Yeast need to be able to handle very harsh environments and it’s important to know how we can help them prepare for the long, dangerous road ahead.
To just name a few challenges yeast need to prepare for:
Oxidative Stress
High Temperatures
Low Temperatures
Ethanol Stress
High/Low pH
Lactic Acid Stress
Yeast Stress Defense (source)
Now, not all yeast starters are created equal.
Sokujo (where we add in lactic acid) does not have ALL the benefits of Kimoto.
Kimoto uses live bacteria, which differentiates it from techniques that use manufactured lactic acid.
Both achieve essentially the same goal of inhibiting bacterial growth and then killing off unwanted organisms by lowering the pH and raising the alcohol over 10%. However, live bacteria in the mash is a categorical difference.
Something is either Kimoto-style or Not-Kimoto-style. Its name only exists to draw comparison.
(Note: that Hiochi bacteria can live in conditions over 20% alcohol.)
Even the name “Kimoto” is a relatively new word. Previously, this is was just known as Kanmoto, to distinguish from the warm weather moto (bodaimoto) (source: aramasa)
What does kimoto look like?
Please check out this wonderful write up on the history of Kimoto by Aramasa
Here you can see an example of the traditional style of kimoto, made with “pole ramming” and this Akita-“technically kimoto”-style.
Conditioning yeast.
Please remember most changes in sake production are about efficiency and quality concerns. And honestly, using the auger just seems like it would be more fun, too…
Here is an overview of an “example kimoto” process:
Note: I’m Skipping over other types of “kimoto” to focus on the most recognizable. Kimoto refers to both a particular process, but also encapsulates any yeast starters that use live lactic acid bacteria to lower the pH, which is… super confusing.
For example: Bodaimoto, yamahai, etc all fall under ‘Kimoto”.
Personally, I think we should rename kimoto to prevent confusion to “The Yeast Starter formerly known as Kanmoto” (as it was named after the style that was popular to brew in the (“cold”=kan) weather.
Ultimately, the kimoto yeast starter is just a progression of organisms that feed on successive food supplies, each provided by the former that ultimately leads to a stable environment that is ideal for yeast propagation. While stable for yeast, it also happens to be fairly prohibitive to the organisms that precede it.
If you just provided water and a food source, this would probably start all on it’s own and proceed to create an acidic environment. Wild yeast might even fall into the mash and start to propagate all on their own.
However, sake brewers noticed certain raw material ratios, timing, and specific actions led to a more active starter and more enjoyable final product.
Below, I’ve split that fine-tuned kimoto process into 3 images.
These are taken from the incredible Nada-Ken glossary.
Day 1 “Mototate”
To produce steamed rice with a firm core, the steamed rice is left unattended for 3 to 5 hours after being steamed at a moderate temperature (25-30°C), either by hangiri, wrapping in cloth, or through other methods. Subsequently, it undergoes 2 to 4 turnings and is left to cool for 5 to 14 hours (ikemeshi), and the brewing process is carried out when the steamed rice temperature is between 12 and 15°C.
The key to this step is helping to breakdown the rice without making a paste, the effect of which will create too much stress on nitrate reducing bacteria and delay or even prevent the succession of organisms.
Some defining aspects of kimoto are how rice is cooled. Specifically, it is commonly “wrapped” and let to sit for hours, forcing a slow release of heat and causing the texture to become “harder” than if it was cooled rapidly. This helps to avoid the aforementioned “paste”. Usually the rice is wrapped around 30°C, and unwrapped when the texture and temperature match the ideals for a particular recipe.
The process of Shikomi is when we combine steamed rice, koji, and water. We often set a "target-temperature” of 7°C because it is the temp that a particular type of bacteria will thrive at, but wild yeast will struggle. This prevents off-flavors or premature fermentation (alcohol production). Our initial focus is generating lactic acid. To prepare for “lactic acid bacteria” we must first provide a food source. In this case, there are bacteria, such as Pseudomonas, which actually feed on Nitrates in the water and break it down to produce “Nitrites”.
Water is the major source of nitrate-reducing bacteria, while koji is what introduces lactic acid bacteria, as well as wild yeast. Lactic Acid Bacteria typically do not aerosolize, so a majority of them don’t “float” into the tank, but rather must be physically introduced. Yeast however, are known to float through the air and can contaminate the batch in this way.
As a general rule, you should assume that in any sake fermentation, koji is your major source for contaminants. In FACT, koji traditionally was how yeast and bacteria would have inoculated a shubo back in the day. (source: Sake Manufacturing Technology, 2023, pg 130) Wooden instruments and other tools, hands, etc. are also contributors, but not nearly as much as a fresh culture from the ideal humid room at 30°C for 48 hr, which is enough to cultivate, not only koji spores, but definitely plenty of generations of yeast and bacteria if conditions are right.
Anyway, for 4-5 hrs after combining the ingredients, temoto is performed. This is done by placing hands and arms into the mash and gently mixing to achieve the softening of rice grains without producing a starchy taste. This also adds bacteria from your skin.
Day 2 (yamaoroshi) “mototsuri”
After 15 to 20 hours the steamed rice and koji have become soft and swollen, the ingredients are crushed called "山卸し” (yamaoroshi) or "酛摺り” (motosuri). Or you can just use the paint-mixer from above.
This is not the soft hand-mix from day one, but rather rough “treading, mixing, or grinding”. Mototsuri is often broken up into 2-3 separate mixes.
In some cases, the first mixing is done by stepping on the rice with one’s feet “酛踏み". Based on the room temp, you might reduce the number of mixes because of how the enzymes perform, melting the rice faster. This is an example of decisions based on intentions, not process.
While not necessary today because of temperature controlled tanks, in the traditional style, moto-tsuri was done in many small tubs. This helped maintain a high surface-area, which kept the temperature low and it was easier to mix. When the moto-tsuri was completed, pairs of tubs were combined together to increase its volume, reduce oxygen, and allow it to hold heat better.
This process is referred to as "折込み" (orikomi, folding).
Day 3 - Utase
As there is now a food source for bacteria, all the tubs are combined so that the Pseudomonas bacteria can begin to consume the Nitrates in the water, and producing Nitrites. The temperature is kept low during this phase and no oxygen is introduced, which is poisonous to bacteria. We want to create ideal conditions for Nitrate Reducing Bacteria.
Two notes:
Many breweries realized that you might need to add Nitrates in order to start this reaction. This can come in the form of salts like Potassium Nitrate.
In addition to salts, brewers may choose to use cultured bacteria strains in order to increase the predictability of a particular recipe. This goes for all Nitrate Reducing bacteria, Lactococcus, and Lacti-lactobacillus in the steps that follow.
Day 5-6
Now that the mash has a higher concentration of nitr-ITES (from nitr-ATES), we can be first warming which will increase the temp 2-3°C a day and decrease 1-2°C at the end of the day. The increase in temp helps cultivate lactic acid bacteria at slightly higher temp range. Each organism has specific ideal temps. Even just 1-2°C can give significant advantage to one or another.
There are two traditional methods… Warm Jug or Bottom heater (you can also use a thermal tank now a days).
One reason for decreasing the temperature each day is to prevent too much saccharification. We want just enough to feed bacteria, not enough to over-stress.
A second reason is that we want longer chain sugars. Bacteria can consume oligosaccharides, where as yeast primarily consume glucose and in fact have a gene that represses the consumption of other sugars if it is present.
Day 13 - Swelling
When the nitrite reaction has ceased, meaning nitrites stop accumulating (we can check this with test strips), it means that the Pseudomonas are now dead and the total acidity is over 1 ml/dl. Nitrates are poisonous to yeast… so we want them completely gone before we pitch yeast.
Now we gradually increase the product temperature to 15-16°C and add pure yeast to induce swelling.
Technically we don’t “NEED” to pitch yeast, but wild yeast are much more unpredictable unless you have “kuratsuki-kobo”, which means you’re brewery is so old, and usually covered in wood, and you are using wooden tubs / tanks (kioke), and they are covered in dominant, self-selected yeast strains from many years of continued brewing.
There is nothing “wrong” or “cheating” about pitching yeast and it is highly encouraged to ensure a successful fermentation.
As the yeast start to ferment sugars and replicate, CO2 expands the volume of the mash. This is known as “swelling”. You need to get your recipe (water / rice) ratio and total volume to tank volume ratio dialed in or it can have the tendency to spill over the side of the tank. Especially if you are using foaming yeast.
Day 14 - 休み “Yasumi” (rest).
Let the yeast do their thing. Take a long weekend. You’ve earned it. They will continue to increase the temperature and depending on the ambient temperature of the room you may need to cool it. We want a controlled rise.
Day 17 - Highest Temp
On day 17, we’ll use the dakidaru or anka method to increase the temp of the mash to 30°C. Yeast will propagate quickly in these conditions if oxygen is present. High temp stress and the increase in alcohol will help kill wild yeast and bacteria.
4 hours is required to double the population. In just 24-48hrs, we’ll see a huge increase in cell count. However, yeast are social creatures. The population will cap out at 2 x 10^8 cells/mL (200M) or 20 Trillion per 100L.
If you consider the cell count, you may realize why it would be important to choose a different shubo ratio. It’s common to use 5-8% of the total mash ingredients to make the shubo. A higher percentage introduces a substantially larger concentration of cells into the main mash and will change the fermentation rate.
Now, we don’t want yeast to “sit” in alcohol for long, which is why we do this temperature increase rather suddenly.
Day 19
After high-temp stress, we introduce… COLD TEMP STRESS. As shown in the Nada-kan diagram above, we need to avoid too much alcohol stress, so as we watch the baume drop to 8, we’ll begin cooling the mash.
This cooling period is known as “wake”, which originally referred to the traditional way of splitting the shubo into separate tubs again, which would help cool it due to increased surface area. You might remember this from the first day or two.
Today, just use glycol jacketed tanks, or ice cold Daru.
The purpose of yeast starter is to grow healthy yeast, not to produce alcohol. Therefore, fermentation must be slowed down at an appropriate time to preserve the yeast.
A standard ABV to shoot for is 10-13%.
Day 21
This is when “karashii” or “rest” begins… meaning we just let is sit for a while at colder temps (10°C from 30°C). Weaker yeast and bacteria will die off in the high acidity, high alcohol, high sugar, and cold temperatures. Too many combined stresses leads to cell-wall failure or metabolism malfunction.
The standard baumé content is 5 to 8, alcohol 10 to 13%, acidity 10 to 11, and amino acidity 6 to 7.
Maturation (wait 5-15 days)
Waiting for several days increases the rate of die off. We want weak yeast or remaining wild yeast and bacteria to die so that we are starting off with only propagating strong, desired yeast.
Use it within (2-30 days)
As seen in the figure above, it takes more than double the time to lose the same amount of viable cells in a kimoto when compared with a sokujo moto. 8-10 weeks vs 2-3 weeks.
Role of the Nitrogen Cycle in Kimoto
It was understood that various organisms played a roll in the kimoto process. Dr. Saito is credited with recording this information in 1930.
A large factor in lactic fermentations is it’s role in the nitrogen cycle.
The Nitrogen Cycle is a key aspect in sustaining pretty much all life on earth, and kimoto fermentation participates in a few of those steps from Nitrate to Nitrite to Nitrogen and finally to alcohol.
For lactic acid bacteria to propagate, they need Nitrous Acid (solubilized nitrite)
In most situations, nitrate in brewing water falls in a legally regulated 2-10g/100L. This can also be added as potassium nitrate if water doesn’t contain any. (for instance: city water, reverse osmosis, or even some wells.
One form of Nitrate comes from decaying organic matter and so you should test for pathogens and other harmful bacteria if your water tests positive for Nitrates before you use it.
The Many Organisms in Kimoto
The following graph is from a study that analyzed the bacteria present from Koji all the way through the moromi in 2 kimoto fermentations….
Despite what it might look like in these graphs, bacteria are not in fact active throughout the full kimoto process or the entire moromi. What we are seeing is the RNA analysis that allows us to identify the organisms that were introduced, but the viability is not being tested, only presence. Regardless, we can see the influence of Koji on the initial moto organisms, and the effect their metabolites have on each other. Then we can see how those organisms fight for dominance as the environment around them changes.
To dispel some common misunderstandings, It is important to note… most microorganisms DO NOT populate the fermentation by the “air”. Especially not lactic acid bacteria, which form localized colonies. In other words, they are not commonly aerosolized. LAB are introduced physically by touching the moto or the koji, and in the case of wooden fermentation vessels, through exposure to the wood. Koji is cultivated for 48hrs in a humid, 30°C room. Humans touch it and transfer their bacteria to to the koji. If instruments are not cleaned well, they might also be a common source for lactic acid bacteria.
In Kimoto starters, the “temoto” step that occurs is often said to be a process to not “crush” the rice, but honestly… my hot take on that is that is was a false correlation. I think that was an assumption that took off, because the biological reasoning of transferring the bacteria to the moto was just simply not understood.
Let’s look at where organisms thrive in the brewery environment
Here are Some notes on specific bacteria…
Identical strains of Leuconostoc mesenteroides were identified on wooden tools and barrels across multiple brewing years, indicating that this spherical lactic acid bacterium (LAB) is likely endemic to the brewery environment. In contrast, Lactobacillus sakei was not found on brewing equipment, and different strains appeared in the starter mash (moto) each year. This suggests that L. sakei is introduced from external sources with each brewing season. (original source)(source)
A separate study found that L. sakei shows reduced resistance to heat stress when grown in low-nutrient environments at around 30°C. While speculative, it’s worth considering that average summer temperatures between brewing seasons have increased notably over the last four decades. This environmental shift may be influencing microbial populations within breweries, potentially leading to changes in the dominant LAB species during fermentation and, by extension, variations in the flavor profile of the final sake. (source)
One study examining six kimoto starter cultures from five different breweries and revealed a notable diversity among nine primary LAB species. Only one shubo followed the traditional progression from spherical to rod-shaped LAB. In another case, spherical Lactococcus lactis remained dominant throughout fermentation. In the other four samples, rod-shaped L. sakei was the predominant LAB.
Researchers suggested that these deviations from the classical model—originally described in the 1930s—may be the result of modern hygiene practices, which have altered the microbial landscape in contemporary breweries. (original source)(source)
It seems like the whole 'transitional' model doesn’t really hold up in practice, so maybe it’s time we rethink what actually matters—and what doesn’t—in kimoto-style fermentations.
What kind of fermentation does this display?
This is actually representative of Lambic beers are also produced in a cold, open ferment with lactic acid bacteria and a progression of various organisms. Check out “coolship” fermentations.
Why are Kimoto Yeast Stronger?
Returning to the concept of “what makes kimoto yeast stronger?”
One of the most interesting fields of research out there takes an organism from one environment and puts it into another or tweak the parameters to see what happens. Another way of saying this is that “genes express themselves in environments”.
In this study, researchers looked at the way temperature differences affect the pigment of rabbits extremities as they develop.
Interestingly enough, we actually have never been able to study yeast in their natural habitat because the very act of attempting to isolate a single test means that we need to control for things that actually can impact their metabolism quite a bit.
We can however look at the macro changes, such as metabolite concentrations and organism behavior. For instance, what if yeast produce more alcohol, or maybe they take longer to produce the same amount. Perhaps bacteria seems to live longer in certain circumstances.
Now, keep that concept in mind for a moment and let’s see what changes researchers have observed…
As phylogenetics go, yeast cells have an ancient gene that prioritizes glucose consumption (lit. ‘glucose repression’), but the working there can be confusing. It means that in the presence of glucose, it represses the consumption of other nutrients. It will simply not consume any other sugars until they are all gone.
Essentially, yeast acts like a kid in a candy store or like a 2 year old that just wants dessert and won’t eat any of their actual dinner. But… it’s not exactly as reckless are you might think. The concept is basically to eat as much as possible in their surrounding environment before other organisms have a chance to. An evolutionary trait, if you will.
In addition to consuming all the food quickly, the byproduct they make is alcohol. Alcohol is typically poisonous to other organisms (even if it just inhibits some sort of metabolic process). So.. its essentially a defensive mechanism.
What even cooler, is that at a later time, yeast can consume alcohol as a food source with the help of an enzyme called alcohol dehydrogenase
But there’s a catch.
Because yeast spend all that time eating junk food, when the time comes to actually defend itself against complex threats, they realize that a food eating contest isn’t really a substitute for proper diet and exercise. They are simply are not prepared for the stresses of their lives.
In a sokujo ferment (where we add lactic acid directly, no bacteria), this is the case and as a result, the yeast are in fact “weaker” in a relative sense and will die off significantly faster in the presence of increased or compound stresses like cold temp, high sugar, high alcohol, etc.
So, did natural selection do them dirty? If they are hard-wired to do this, what can yeast do to defend themselves?
Here’s where Kimoto gets interesting.
“Through a serendipitous accident, [it was] discovered that bacteria have the capacity to induce [an] epigenetic element in yeast.” -source
This image shows that in a medium containing only Glycerol, non-metabolizable glucosamine, and Lactic acid Bacteria…. it will trick the yeast into reversing their glucose repression, and will successfully metabolize glycerols.
That epigenetic element is referred to as [GAR+].
I have read it is also described as Prion-like, which is essentially a mis-folded protein. Suffice it to say, this is a huge breakthrough in understanding yeast and lactic acid bacteria biology. Specifically how they communicate with yeast.
What we are seeing here is lactic acid bacteria and yeast symbiosis. When yeast is co-cultured with one of many lactic acid bacteria strains (about 30% of all strains share this ability), the bacteria produce a chemical signal that will “induce the [GAR+] prion” in yeast. This reverses the gene repression triggered by glucose (word this better). The signal switches yeast from a “specialist” to a “generalist” so they consume or process other types of sugars such as glycerols.
Different ways Glycerols are produced in sake (directly: glycolysis, indirectly: koji enzymes)
Glycerols are actually a product of glycolysis (how yeast make alcohol) and more or less just something yeast make and then stock pile. So, even when yeast are eating glucose, they are also producing glycerol. I suppose you could say this is like a 1 yr old who throws their broccoli on the ground?
The koji enzyme, lipase, ALSO produces glycerols by breaking down Lipids.
Glycerols (a simple type of sugar-alcohol) are known to help yeast strengthen cell walls. They accumulate in the cytoplasm (fluid in the cell), which prevents loss of water through osmosis (resistant to osmotic pressure). Like an “inner scaffolding to keep the cell’s shape”, preventing cell rupturing and allowing cells to maintain important functions like passing nutrients and waste through the cell wall even under extreme stress.
In my brain, this is like pumping this yeast full of steroids and sending them to bootcamp.
Yeast, like other organisms, possess an ability to adapt to their environments. They do this by augmenting their own cell walls, through real-time social responses, and even producing off-spring are more tolerant of various stresses.
There are many different ways to pass changes to an organism to its progeny:
Survival / Selective Inheritance: Darwinism and Lab Techs. Real Jeff Goldblum territory here. “life, uh… finds a way”
DNA Mutation: This is more permanent and involves a permanent change to the lineage. A very common way to create new strains of yeast or other single cell organisms by blasting them with UV light.
DNA Methylation: Involves methyl group that randomly turns off various genes
Non-Genetic Inheritance: Prions “misfolded proteins”, which are passed in cytoplasm during mitosis.
In this particular case… the [GAR+] prion is passed through Non-Genetic Inheritance.
So yeast can actually pass this [GAR+] prion in the cytoplasm when their cells divide. This is an example of Non-Genetic Inheritance. But it is considered “heritable” because it isn’t coded into the DNA. In other words, it could disappear after a few generations, but studies show that in a lab setting, it actually lasts for many iterations.
When I showed this next graphic at the conference, there was some confusion over this next slide because it must have looked like a different graph, but I have gone back and referenced several sources (source 1, source 2) to ensure it was correct.
What you are seeing is the increase of alcohol over the course of 10 weeks, with each yeast starter (shubo) being left at a constant 10°C. As the white dots increase (alcohol content), the black dots (viable yeast cell count) decrease.
Typically we would “crash” the temp to 5-8°C, which helps kill off more bacteria and weak yeast, but in this case, this test was to show how the yeast resist alcohol stress, so the temp was left higher. In just 2-3 weeks, over 80% of the Sokujo style moto’s yeast cells died. However, the kimoto yeast cells, strengthened due to their reinforced cytoplasm and cell walls, experienced 2-3x as much longevity.
What makes kimoto taste more “rich”?
Somethings you might have read out there include:
“due to the way it’s made”
“flavors develop toward the end of fermentation due to strong yeast in a high alcohol environment” (stress?)
“kimoto makes more amino acids”
etc.
I’m going to reference a paper that one of our Guild members wrote recently. Since this has been a topic of much discussion, we’ve been passing various published papers back and forth to dig into the “why” of kimoto.
Aaron Meldahl is a chemist and sake aficionado who lives in Tokyo and goes by the handle @the.sake.explorer
Aaron took on the colossal task of organizing lots of this research into an extremely well written article and has started a youtube series we are very much promoting to help spread all this good knowledge.
Let’s start with how kimoto sake is described:
Aaron compiled this list of key works from various sources that illustrate the confusion, often using contradictory terms:
“rich, mellow, rough, gamey, funky, fine-grained, complex, mild acidity, high acidity, wild, rustic, savory, etc”
There are MANY aspects of flavor this we can focus on, but for the sake of time, I’m going to discuss one very important aspect of kimoto.
I will say, as far as most of the descriptions out there go on what “causes” the flavor of Kimoto, I would highly recommend for anyone brewing or selling kimoto that they read Aaron’s paper when it is published. He summarizes many important details from various studies and it really flips a lot of the current ideas on its head.
But today, I want to talk about Amino Acids. Specifically, D-Amino Acids. Amino Acids and Peptides are like “nature’s secret spice rack”. Without them, things taste cleaner and lighter. In abundance, they taste richer and you get to say that word “umami” to impress your sake-newb friends.
Amino Acids and Peptides are created by proteases that come from Aspergillus as well as Yeast during glycolysis. In Kimoto, bacteria also contribute to the pool of amino acids as well, BUT in a way that is specific to lactic acid bacteria.
Before we get into that, let’s just look at how amino acids contribute to flavor.
Most of what we learned about taste perception on the tongue has been dispelled by modern science. For instance, We do NOT have areas of the tongue for different tastes like salty, sweet, sour, umami, and bitterness.
Every part of the tongue experiences all of these. However, some are more sensitive to specific tastes, but there is no “MAP” of the tongue as it was once believed
A revelation like this in the 20th and 21st century is like when plate tectonics was confirmed in the late 1960s and it became the central unifying theory of geology. Many of us were taught that the earth’s core is molten lava… that’s not true.
Amino Acids press down on various sensors, and those sensors play a musical note in our brain. They can create consonance or harmony based on which “sensors” are being pressed by the molecule.
Now we don’t have time to get into flavor perception, but for the sake of this article, remember that each amino acid and combination of several amino acids or chains of amino acids will essentially play a different chord. You will either like it, or love it, or hate it.
Here is how we experience Amino Acids in Sokujo Moto
Notice the level of “bitter” amino acids highlighted in red:
And HERE is how we experience Amino Acids in Kimoto:
While some amino acids will remain that express bitterness, Lactic Acid Bacteria are now giving us a whole NEW set of flavors.
Notice the flavor perception change? That’s a lot of sweetness. This is another topic that Dr. Takahashi introduced me to and it is such a critical part of understanding Kimoto’s flavor.
Lactic Acid Bacteria possess the ability to change many naturally occurring L-Amino Acids into their D-Amino acid form. This is achieved by a process called Racemization.
The scary scientific term for these two opposite molecules is: Stereo E-nan-tiomers
Basically, these are amino acids that are mirror images of each other. Lactic Acid Bacteria have the ability to not only produce these, but can uptake existing bitter L-amino acids and convert them to their sweeter, D-amino acid form
What does that mean?
Well, for the sake of this article, you need to know that they are both constructed with the same atoms, so they are in fact the same molecule, with one large difference: they have been rearranged to have a different configuration.
What this means for us is that our taste buds will experience a different “chord” and we will sense a completely different flavor.
As an example:
L-tryptophan is approximately half as bitter as caffeine
D-tryptophan is 35 times sweeter than sucrose (source)
So, try to imaging a +15 SMV (dry) Kimoto that has a Total Acidity of 2.2, but it tastes sweeter than a -10 Sokujo with a 1.8 TA.
Now… not distract too much from the previous point, but I want to make a quick note on peptides.
Peptides are just short chains of amino acids.
It’s often said that Kimoto contains a higher amount of peptides, which contribute to overall mouthfeel such as richness, silkiness, and can actually contribute to bitterness as well. This is partially true, but not to the degree that is often described.
Sokujo shubo is known to create far fewer amino acids due to the lack of bacteria, where-as Kimoto contains a much larger amount.
To quote Aaron again:
In the high-amino acid kimoto environment, the yeast preferentially takes up amino acids over peptides. In fact, it is known that certain amino acids can even block peptide uptake by suppressing specific gene expression. In the comparatively low-amino acid sokujō environment, yeast takes up more of the small peptides instead, leading to a greater decrease in their levels.
It is important to note that the differences between kimoto and sokujō in this case seem to be due to differences in kōji enzyme activity and yeast metabolism in response to different pH and amino acid concentrations, not the presence or absence of LAB itself.
This is an incredible super power and all due to the symbiotic relationship of lactic acid bacteria and yeast
This is a topic for another day, but yeast actually alters their metabolite production to “overflow” their amino acid production in the presence of LAB in order to help the the bacteria survive longer (source). There are even more sources like this that are full of fascinating studies that are slowly, but surely, expanding our knowledge of collaboration between organisms.
Looking back on the research I’ve done over the last few years, it’s exciting to be able to say that I have a much more solid understanding of the ecosystem surrounding these organisms and how we can augment the environment to coerce their activities to meet our desired outcomes.
Coupling this research with my focus from last year, I see a fundamental connection between the organisms from the rice paddy, all the way to the bottle. Aspergillus Oryzae, Lactic Acid Bacteria, and Saccharomyces Sake seem to share many bonds that predate human existence.
To end on a fond memory…
I feel a great sense of joy looking back on the days I spent listening to Dr. Takahashi explain stereo enantiomers to me by holding up her hands and explaining the taste difference between one vs the other. This was just a fraction of the curiosity that she empowered me with.
In reciprocity, she told me that I helped her practice English when I was staying with her in Hawaii. I suppose that is a nice way to make me feel like I gave something back.
But isn’t that what it’s all about. Both of us, contributing to the other’s growth.
It goes to show you how important these symbiotic relationships are to all of our success.
Dr. Takahashi... To whom I owe so much.
