Why you should want to use sauerkraut to heat your room

A definitive guide by N. Ong and J. Ong

What is Sauerkraut?

Months into the pandemic that is COVID-19, we, as the human race, have come to see different sides of every part of life, adapting to new normals and adjusting to rapidly shifting conditions. Many of us have heard the siren call of the sourdough evangelists, and it has become a new normal to see bubbling starters litter social media feeds. Baking has become the banner of the “stay at home” movement, and the sourdough starter is its champion. As much as I would fancy myself a budding baker, I count myself among the large and unlucky group that has tossed out more than one failed starter. They can be fiddly, unruly, and misbehaving creatures, fickle beyond compare. This is why I would suggest an equally primeval alternative fermentation, one that is sturdy and indefatigable, rugged and unrelenting. The humble prince of bacterial fermentations: our reliable friend, sauerkraut.

We all know sauerkraut. That delicious, funky, fermented, sour cabbage swipe across the palate that makes a wonderful accompaniment or a central focus of a meal. Sauerkraut isn’t just the stuff you eat with pork on New Year’s or stuffed in a Reuben with corned beef, it’s a powerhouse in its own right, in every sense of the word. The fundamental processes of all bacterial fermentation (think kimchi, pickles, yogurt, cheese, soy sauce, salami, and yes, sourdough) occur with astounding regularity and astonishing simplicity in a dish consisting solely of cabbage and salt. Giving a shredded head of cabbage a massage with some salt and letting it sit submerged in its own expelled water for a time provides a fermentation base upon which all human civilizations have built, and will continue to do so for as long as we exist. As this pandemic has shown, we are a species whose fate is intertwined with colorful strands of fermentation.

Sauerkraut is a food that not only nourishes our palates and cultural histories, but our gut microbiomes as well, containing millions upon millions of healthy probiotics that some say will do everything from fighting inflammation to lowering the risk of cancer. Despite the innumerable benefits we reap from its bountiful shores, perhaps the most overlooked contribution of sauerkraut is its potential for providing our homes with natural heat. Stave off those cold winter nights with a warm bellyful of sauerkraut, a shot of gut-healthy kraut juice, and a heater plugged not into an outlet, but the warm walls of live fermentation.

The techniques used to make sauerkraut are among the simplest of any fermentation. At its core, sauerkraut is a mixture of shredded cabbage and 2% of its mass in salt. It doesn’t require timed feedings or special ingredients like that blasted starter, and from the moment it’s packed into a jar, the process is hands-off. The combination of mechanical pressure from mixing or massaging the cabbage and the osmosis due to the addition of salt causes the cabbage to expel the water inside its cell walls, releasing fermentable sugars and nutrients that aid in the fermentation process. This nutrient-rich nectar submerges the cabbage, preventing air from reaching the bulk of the fermentation. Keeping air out of the cabbage mixture helps prevent the growth of unwanted microorganisms while aiding the process of fermentation. The simplicity of sauerkraut production belies the complexity of flavor that results from the ceaseless work of legions of microscopic bacteria that live, work, and die continuously during lactic acid fermentation.

Lactic Acid Fermentation

Sauerkraut is an ancient fermented food made of cabbage that takes on a sour (“sauer”) taste due to a process called lactic acid fermentation (LAF) which involves the creation of sour lactic acid to kill harmful microbes and preserve food for up to months at a time. This process converts glucose (C6H12O6) into lactic acid via pathways created by several strains of lactic acid bacteria. Lactic acid bacteria exist naturally everywhere, between leaves of cabbage, on our fingers, and in the air. The multi-week lifespan of an active LAF involves the rise and fall of several cultures of lactic acid bacteria, akin to the rapid succession of dynasties in a heavily-contested geopolitical region. Whether by conflict or lineal inheritance, monarchies and bacteria show us that there is far more to any story than the precise composition at the current moment, and that to get the full picture, we need to look at things through a time-varied lens.

Photo by CDC on Unsplash

The first of our superstar bacterial strains is Leuconostoc mesenteroides, a springy upstart heterofermenter, meaning that it produces multiple products, including lactic acid, ethanol, and gas. L. mesenteroides has a strong salt tolerance, which means that it can tolerate the fairly high 2% salinity of the fermentation, while other bacteria might not. This gas-producing coccus quickly drops the pH of the solution of salt and cabbage juice, which helps inhibit the action of other microorganisms and pave the way for the next wave of lactic acid bacteria.

When the pH of the solution reaches 4–4.5, L. mesenteroides dies off, giving its life for others. The acid that it has created provides a favorable environment for the Bonnie and Clyde of the cabbage fermenting world, two take-no-prisoners bacilli that we call Lactobacillus plantarum and Lactobacillus brevis. While L. Brevis is a heterofermenter like L. mesenteroides, L. plantarum rushes in like a southpaw, a homofermenter focused on one thing only: creating more acid. L. plantarum is a notable bacterial strain in the sauerkraut process, as it creates 2 moles of lactic acid for every mole of glucose, producing a great deal of the acidity that gives sauerkraut its signature tang.

These lactobacilli will continue to create more and more lactic acid in the solution until its pH reaches 3.6, at which point they give way to Lactobacillus pentoaceticus, which ends the fermentation process. At this stage, any more lactic acid produced inhibits the growth of lactic acid bacteria because of the highly acidic conditions, and thus the fermentation reaches somewhat of an equilibrium, keying the line between highly-developed flavor profiles and uncontrolled rotting.

One of the essential take-aways from heterofermenters and homofermenters is that both are represented by chemical reactions, which have reactants, products, and some form of energy transfer. By Hess’s Law, we can see that the enthalpies of formation for products are lower than the enthalpies of formation for reactants, which means that some energy must be released during the reaction to balance the equation- this is an exothermic reaction. In other words, lactic acid bacteria turn cabbage into sauerkraut, and in doing so, they release energy in the form of heat.

(L. mesenteroides) Heterofermenter:

Heterofermentative reaction

This exothermic reaction has a standard enthalpy of reaction of approximately -91.88 kJ/mol of glucose consumed.

(L. plantarum) Homofermenter:

Homofermentative reaction

The standard enthalpy of reaction is approximately -114.86 kJ/mol of glucose.

We can see that homolactic fermentation with L. plantarum produces more energy than does heterolactic fermentation with L. mesenteroides and L. brevis, and given several key ideas about the process of sauerkraut production, we can finally begin to ask the question that we should all be asking. How much cabbage do I need to heat my room with sauerkraut?

Sauerkraut as a space heater

In this analysis, we aim to show that the exothermic nature of the lactic acid fermentation of sauerkraut can provide enough power to replace a standard electric space heater. For this model, we’ll assume that we want to generate 800 W, which is a reasonable power rating for a portable ceramic heating system that one might use to heat a room. Ask not what you can do for sauerkraut, but what sauerkraut can do for you. It can do a lot.

Considering the average of the enthalpy of reaction for the homofermentative and heterofermentative processes, we arrive at 103.37 kJ/mol glucose as the standard heat generated in a fermentation process. Based on several sauerkraut fermentation recipes, we can assume that at room temperature, the time to complete the fermentation process is approximately 2 weeks.

Avg. energy released = 103.37 kJ / mol glucose

Time to complete fermentation = 2 weeks = 1,209,600 s

For every mole of glucose broken down, the sauerkraut fermentation process will release 103,370 J of energy. That’s more than enough energy to burn 2.63 grams of fat! Because we want to equate our energy release to power, measured in watts [W], we need to convert our energy release to an energy per time basis.

Avg. power of fermentation = 0.085 W / mol glucose

Working in terms of moles isn’t very helpful when dealing with real-world quantities like the number of heads of cabbage, so we’ll need to convert our problem to deal with grams of glucose instead of moles of glucose.

Molar weight of glucose = 180.15 g / mol glucose

Avg. power of fermentation = 0.000474 W / g glucose

The next step requires some nutritional information about cabbage and sauerkraut. Cabbage is turned into sauerkraut as lactic acid bacteria consume available sugars in the cabbage, producing lactic acid, energy, and secondary products. Nutritional data gives us the amount of sugar in standard raw cabbages, but not all this sugar is consumed in the fermentation process. Sauerkraut still has sugar in it, however far from sweet it seems. Using nutritional information about sauerkraut and cross-referencing with tables for the static fermentation of glucose, we can see that most, but not all of the sugar is converted to lactic acid.

Glucose in raw cabbage = 0.032 g glucose / g cabbage

Glucose consumption in fermentation = 85%

Effective glucose consumption = 0.0272 g glucose used / g cabbage

At this point, we can see that our power of fermentation can now be expressed in terms of grams of raw cabbage needed. This allows us to begin to get a better picture of how much cabbage we need to heat our room.

Avg. power of fermentation = 0.0000129 W / g cabbage

Given a space heater of 800 W, how much cabbage do we need to produce the same amount of heat? The answer: 62,001,559 grams of cabbage. That’s 45 Toyota Prii of fermenting cabbage needed to replace just one small space heater!

With a large cabbage head weighing in at an average of 1,106 grams, we can see that we’ll need 56,060 cabbages. This leads us to a new unit of measurement that we’ll call CPW, or cabbages per watt, a new unit of power.

800 W equivalent = 62,001.56 kg cabbage

CPW¹⁴ (days of fermentation)= 70.074 cabbages / W

Some might say that this amount of cabbage is unreasonable, and that buying 62,000 kg of cabbage is a social faux pas, especially when it is to be used solely to replace a room heater. For someone who already hates the taste of cabbage or sauerkraut, this is certainly a tall order. Even so, it’s an important number for any enterprising person who dreams of sauerkraut, and should that enterprising person consider selling their sauerkraut on top of getting a free 800 W of heating power, they should read the section Is it really worth it though? in the appendix.

The original question at hand remains to be answered explicitly, despite a great deal of text that may or may not have convinced you that sauerkraut is something worth your time. Should you heat your room with sauerkraut? The answer is not crystal clear. There are countless debates to be had on every forefront of modern dialogue, spanning issues political, environmental, and practical. Chemical reactions have seeped in cultural influence in the same way that bacterial action implicates policy and perception. The cabbages you might want to ferment may have been coaxed to maturity by unfairly compensated farmers, and the carbon dioxide produced by the fermentation may add a non-negligible weight to your carbon footprint. The impacts of every action we take can unleash a train of events so far-reaching that we stutter to a halt, paralyzed by a deluge of information.

Whether we, as human beings, choose to engage with the hubbub is entirely up to us. Whether we choose to ferment cabbage to make sauerkraut is also our choice to make. Instead of zooming out and taking in a macroscale jammed with the clash of ignorant armies at night, zoom in very close. You’ll see the exquisite details that fill us all with child-like wonder and the crazy applications that are wild enough that they might just work. Zoom in even closer and revel in the delights of exploration, and walk the halls of science like an ever-growing museum. Even the most insignificant of details will call out, telling you that “I am large, I contain multitudes.” Listen to them, those cabbages in the supermarket, those tiny stars in the sky.

The value of using sauerkraut to heat your room may well be a farce of extremities, especially when taken under the guise of practicality. It is my belief, however, that sauerkraut heating’s true value is intrinsic, a genuine appreciation for the beauty of the world around us. With or without 56,000 cabbages, that beauty is provoking enough to consider, at the very least, what life would look like with a sauerkraut room heater.

Appendix

Keeping it cool

Of course, everyone is worried about the possibility of bacterial suicide via fermentation-generated heat. A very basic look into the fermentation’s heat transfer should assuage that issue.

The fermentation would occur in a large 1000-gallon HDPE tank with the following specifications:

  • Inner radius: 0.8128 m
  • Outer radius: 0.8106 m
  • Height (L): 1.9685 m
  • Thermal conductivity (K) of HDPE: 0.465 W /(m K)

Assuming the system temperature of 20 degrees Celsius (ideal temperature for the propagation of L. mesenteroides) and a convective heat transfer coefficient (h) for air of 100 W /(m² K), the model is then highly simplified to a cylindrical shell with only thermal conductive (from the tank) and convective resistances assumed present.

Further assumptions for simplification:

  • Steady State heat transfer in 1-D (radial)
  • No contact resistance or radiation
  • Constant properties throughout

If 35 drums tanks produce 800 W, the per-drum wattage of 22.86 W is the heat produced (Q).

Heat transfer in a barrel of sauerkraut

Convective thermal resistance:

Convective thermal resistance

Conductive thermal resistance from the tank walls:

Conductive thermal resistance

Knowing that heat transfer is given by the temperature difference over the thermal resistances (Q = deltaT / R), we can use a simple equation to find the internal temperature of the cabbage. The resulting cabbage temperature is 20.03 deg C, barely a fraction of a degree above ambient.

The almost negligible change in temperature should calm anyone concerned for their cabbage, as the bacteria can operate without worry. Even dramatically changing the heat transfer coefficient and thermal conductivity results in little temperature change.

Is it really worth it though?

You might be thinking to yourself that this seems like a lot of work for nothing. 45 midsize cars worth of cabbage couldn’t possibly justify replacing a little ceramic space heater with a sustainable and eco-friendly source of probiotic heat. Whatever your qualms, and I’m sure there are many, we will see that the numbers strongly encourage you to partake in a sauerkraut operation. It is worth it indeed.

We’ll break down the costs associated with running the space heater continuously for two weeks and compare that to the costs and benefits of making and selling such a large quantity of sauerkraut.

Space Heater

Base cost = $69.99
With tax = $74.19
Cost of electricity in Pennsylvania = $0.1375 / kWh
14 day electricity cost = $36.96
Total cost = $111.15

Sauerkraut

We can break down the sauerkraut process into fixed costs, variable costs, labor, and revenue. These factors will sum to the total profit/operating loss generated by the sauerkraut.

Fixed Costs

Assuming that each large head of cabbage, once shredded, produces a volume of 10 cups, we can figure out how much storage we’ll need to ferment the cabbages.

Total volume of shredded cabbage = 132.6295 m³ = 35037 gallons

This is an extraordinary amount of cabbage, and would almost fill a 20’x40’x6’ swimming pool. Truly, what better use is there for an in-ground pool? We can subdivide the cabbage into 35 entire 1000 gallon plastic drums. Even though the volume of cabbage shrinks dramatically as salt is applied and water is expelled, we’ll use 35 drums to provide redundant storage space in the case of variations in cabbage size.

Cost per tank = $647
Number of tanks = 35
Cost of tanks = $22,645
Sales tax in PA = 6%
Total fixed cost = $24,003.70

Variable Costs

Sauerkraut is composed of only two simple ingredients: salt and cabbage. Add time, and you’ve got yourself one of the most potent traditional sources of beneficial gut bacteria and flavor.

2016 estimated costs for a ton of American-grown cabbage for processing were $228. While international sources like Alibaba supply cabbage in the range of $150–400, the cost of shipping and volume of trade can be prohibitive to some sauerkraut supply chains.

Because sauerkraut is usually made with a salinity of 2%, we’ll need 2 grams of salt for every 100 grams of cabbage, or 1,240 kg of salt in total. The cost of Himalayan pink salt was taken from bulk packages on Amazon.

Cost of cabbage = $228 / ton
Total cost of cabbage = $15,582.66
Cost of Himalayan pink salt = $2.56 / kg
Total cost of salt = $3,174.48
Total raw ingredient cost = $18,757.14

Labor

To process all that cabbage, it would be best to purchase an industrial machine to chop it all. In this case, however, we’ll consider low up-front business costs, and simply hire workers to perform the manual labor instead. Because this is an unskilled job, we’ll pay workers above minimum wage in Pennsylvania ($7.25/hour) and require them to be able to process (wash, chop and rub with salt) a cabbage in less than 12 minutes. Our analysis assumes a total labor cost, which could be split among a few workers over a year, or by a great number of community members over a short period.

Labor = $8.50 / hour
Processing time = 12 mins = 0.2 hours
Total hours required to process all cabbages = 11,211.9 hours
Total labor cost = $95,300.77

Assuming that cabbage processing occurs in a facility separate from the room we wish to heat with the sauerkraut fermentation, we’ll need to ensure that the cabbage is kept at ideal fermentation conditions, using an AC or heater throughout the year.

Power for a large AC unit / heater = 1440
Hours in a year = 8,760 hours
Total cost of maintaining a stable temperature year-round = $1,734.50

These costs are optional, as they may not pertain to a particular business model, say if the cabbage processing were to occur over a shorter period, but they are included in the calculations to add additional room for error.

Revenue

Comparing this sauerkraut to major competitors in the market, we can set a reasonable price to sell the sauerkraut produced by this room-heating adventure.

Price comparison of current market

We can see that Wildbrine has the lowest cost of the three major raw sauerkraut suppliers on the market, so we set our sauerkraut product to the same cost. General calculations performed thus far have been in terms of cabbage needed, so we’ll need to convert cabbage and sauerkraut volumes for sale. Most recipes equate 3 pounds of cabbage to a final product of 4 cups of sauerkraut, which is an imperfect conversion on many levels, but will serve our purposes for this broad analysis.

Cabbage-Sauerkraut conversion = 2.268 g cabbage / g sauerkraut
Total sauerkraut produced = 27,333.5 kg sauerkraut

Assuming that we’ll only retain 70% of these sales due to marketing, advertising, and distributor fees, we can calculate the final revenue generated by sauerkraut sales.

Total revenue = $171,781.66

Total Profit

The total profit of using sauerkraut to heat your room, but factoring in the costs and benefits associated with sauerkraut production is the sum of the fixed costs, variable costs, labor, and revenue.

Total Profit = -$24,003.70 - $18,757.14 -($95,300.77 + $17,34.50) + $171,781.66
Total Profit = $31,985.57

Price comparison for heating

We can see that sauerkraut handily beats the space heater by a margin so considerable it’s almost laughable to think that anyone with the right entrepreneurial spirit and time on their hands would ever consider buying a space heater. That being said, we acknowledge and support the ways we can use technology to make our lives easier, and space heaters are most certainly easier. However, should the world run out of space heaters or lose all grid connectivity, it’s comforting to know that there are more things than campfires that we can huddle around.

I love learning about anything, really. As a curious person, I’ve always been fascinated by how very distant fields can interact. Fermentation enthusiast.

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