Rejuvelac is essentially a natural (yeast and lactic) fermentation of sprouted grains.  One person quoted something to the effect of at its peak it is a pleasant tonic, but fermented too long or fermented wrong, it is simply putrid.  If the grains were rye, it could be called Kvass (Russian or Slavic origin). There are three general steps:

Soaking Sprouting Fermenting

The soaking and sprouting steps are essentially the same as “sprouting” in the food code or in FDA guidance.  Sprouting grains should be carried out in acidified water OR at refrigeration temperatures.  Ambient temperatures are not needed for seeds or grains to sprout.

Use canning citric acid powder to acidify tap water to pH ≤ 4.2.  Sprout grains in the acidified water at ambient temperatures.  Alternatively: sprout grains in plain tap water under refrigeration ≤ 41F.  Both of these methods will prevent ALL foodborne illness bacteria from growing.  Yes, Listeria monocytogenes can grow at ≤ 41F, but it grows VERY slowly.  Please see this LINK for an inexpensive and recommended pH meter.

After sprouting, the sprouts and husks are rinsed in potable water.  The acidified water is not needed for the rinse.  Fermentation is the next step.  Water is added to the sprouted seeds.  An ACTIVE culture should be added.  A wild fermentation is not recommended.  One concern with this process is the possible presence of bacterial pathogens.  Salmonella has been implicated in foodborne illnesses in sprouts and Bacillus cereus in grains and rice.  Note that Kvass and sourdough bread processes have a heating step and baking step respectively.  Rejuvelac does not.  In fact it is advertised as ‘raw”.  The control, therefore, is to have a culture that is active and ferments rapidly.  An active culture provides competitive inhibition, reduces available nutrients and lactic acid bacteria fermentation reduces the pH.  The concern then is that if one relies on the natural wild biota to grow from a few cells to many, during this time, pathogens can also grow from a few cells to many.

Add an ACTIVE fermentation culture.  Choose one of three methods.  1. Use a commercial dried or freeze dried culture.  2. Use a culture from a very recent successful previous batch.  3- Create a mother culture from wild microorganisms.  No 3. is essentially making a mini batch solely to grow an active culture.  An active culture is a necessity to minimize foodborne illness bacterial growth until fermentation reducing the pH of the Rejuvelac first to pH ≤ 4.6, then preferably to pH ≤ 4.2.  generally, Rejuvelac is fermented in 1-2 days at ambient temperature.  If it takes longer than this, it is a sign that the culture was not ACTIVE and the batch should be discarded.

A natural sprout biota (wild) culture will likely be a mixture of yeasts and lactic acid bacteria (think sourdough bread). The natural culture is allowed to ferment the sprouted grain water producing a yeasty (bready) smell along with a lactic acid sourness.  A purchased culture is more likely to be a lactic acid bacteria that will produce a yogurt like smell that has less of a bready smell.

Quality Control - Refrigeration
Rejuvelac that has been fermented to pH ≤ 4.2 is no longer TCS (temperature control for safety).  It does NOT have to be refrigerated for food safety.  Refrigeration is therefore solely for quality.  This means that if you were to transport or sell Rejuvelac at ambient temperature (e.g. at a farmer’s market), it could remain outside of refrigeration safely.
Soaking All pathogens Refrigeration ≤ 41F
Sprouting All pathogens Refrigeration ≤ 41F or acidify to pH ≤ 4.2
Fermenting All pathogens Ferment with an active culture dropping the pH to ≤ 4.2 as rapidly as possible
Aging At pH ≤ 4.2 no pathogens can grow* Refrigeration ≤ 41F for quality (not safety)
*it is possible that if E. coli O157 or Salmonella were present they could survive.

Traditional tempeh is made from mold fermented soybeans. Whole soybeans are soaked, dehulled, cooked, cooled, and fermented. Specialty tempeh may include other sources of starches such as beans or whole grains.

From a food safety perspective,
tempeh is analogous to the hazards of sushi rice.

Sushi rice is soaked and cooked with the intention of warm holding for an extended period. Tempeh is soaked and cooked with the intention of fermenting at 30C for 24-48 hours. In both, the cooking process eliminates vegetative pathogens. This leaves the three spore-forming pathogens as hazards.

Spore forming pathogen Possible Control Measures
C. botulinum pH ≤ 4.6; presence of oxygen, competitive microbial cultures
C. perfringens pH ≤ 5.3; presence of oxygen, competitive microbial cultures
B. cereus pH ≤ 4.3; competitive microbial cultures

Tempeh soybeans, beans, or grains are soaked to hydrate them from their dried state. Hydrating these starches also hydrates the bacterial and mold spores present. Therefore, it is safest to hydrate at refrigeration temperature. Alternatively, the soaking water can be acidified to pH ≤ 4.3 by adding a mild acidulant such as vinegar, lactic acid, or acetic acid. High acid levels inhibit the three spore-forming pathogens. Later, during fermentation high acid levels will favor mold growth over growth of spoilage microorganisms. This acidulation step is not traditional but is analogous to food safety changes made to traditional preparations of sushi rice.

Once hydrated and dehulled, the starches are cooked. As noted above, cooking eliminates all of the vegetative pathogens, leaving just the three spore-forming pathogens a concern.

After cooking, the dehulled soybeans are spread thin to cool. Spreading the starches thinly exposes all of the surfaces to air. Oxygen will prevent Clostridium growth and may lead to lethality. It is noted that there will likely be anaerobic areas. Bacillus cereus is facultative. Acidulated starches will prevent growth of the spore-forming pathogens regardless of the presence or absence of oxygen.  If starches are not acidulated to pH ≤ 4.3, then rapid cooling is required (130-70F in ≤ 2h) to prevent spore-forming pathogen outgrowth and possible toxin formation.

Historically, the competitive microbial culture in tempeh was a Rhizpus (R. oryzae or R. oligosporus) usually originating from a banana or plant leaf the cooked soybeans were wrapped in. Today, a tempeh culture can easily be purchased. Starter spores are sprinkled onto the surface. The tempeh is allowed to ferment at about 30C for 24-48 hours. If using a quality starter culture, the mold will grow rapidly in ≤ 4h (functioning as a competitive antimicrobial culture). After 24-48h the tempeh will be held together by white mold mycelium indicating a successful ferment.

from wikimedia white mycelium with black sporangiospores

After 48h the tempeh culture may sporulate producing dark or black spores. This is not harmful, but is considered a quality defect. Likewise, fermenting past 48h may develop ammonia byproducts reducing quality and increasing the pH. An increase in pH is less of a concern to food safety at this point, since an active (competitive inhibitory) mold culture is present.

Tempeh is best stored frozen.  If kept refrigerated it will over-ripen in about 2-3 days (black spores and ammonia).   If left at ambient temperature it will over-ripen in 12-24h.  An additional food safety hurdle is that most tempeh is fried or deep-fried.

For some additional details on Tempeh consult The Book of Tempeh (Wm Shurtleff).

Black garlic is “hot fermented” fresh garlic (Allium sativum) has been produced in several Asian cultures for centuries.  Full bulb garlic is kept at a controlled high temperature (60–90°C | 140-195°F) and high humidity (80–90%) for a week to several months.  A Maillard reaction (browning) turns the garlic its black color.  Natural biota (bacteria and yeasts) capable of growth at these high fermentation temperatures contribute to some chemical changes, while the heat of the process results in other chemical changes.  In the end, the garlic is sweeter, lacks allicin (sulfur bitterness), and is umami-rich.  Unfortunately, there is little research-based information on the “fermentation” characteristics of black garlic.

Food Safety | The “fermentation” temperature MUST be at 57°C (135°F) or above.  Failing to maintain this temperature control could lead to foodborne illness.  Foodborne illness bacteria will begin to grow at temperatures just under 57°C (135°F) including Clostridium perfringens and Clostridium botulinum.  The toxin produced by C. botulinum is the most potent and deadly toxin known to man.  For that reason a temperature datalogger is recommended.  This tool will monitor temperature for many weeks.  The data can be downloaded to a computer file.  It is advised to place the datalogger unit outside the fermentation chamber and the probe inside.  Prolonged exposure to the warm temperatures and high humidity can shorten the life of the datalogger unit.

The black garlic fermentation is quite different than a traditional vegetable fermentation like sauerkraut (cabbage) or pickles (cucumbers).   Both cabbage and cucumbers have natural (biota) lactic acid bacteria that rapidly ferment the vegetable sugars in a salt brine at ambient temperatures.  This rapid fermentation inhibits the growth of pathogens like C. botulinum.  Once the brine reaches an acidity pH of 4.6 or less, C. botulinum cannot grow.  The black garlic fermentation may or may not result in an acid fermentation.

The post-fermentation properties of the black garlic determine how it must be stored for safety (ambient or refrigerated).

  • If the pH is ≤ 4.2; the black garlic may be packaged for ambient (room temperature) sale.
  • If the pH is > 4.2; the black garlic must be refrigerated or,
  • If the pH is > 4.2; and the Aw (water activity) is ≤ 0.85, the black garlic may be packaged for ambient (room temperature) sale.
    Note that water activity meters are expensive (> $2,000).  Some food testing labs will test a sample for Aw at $10-$30 each.

Black Garlic Production HACCP CCP Summary

Fermentation temperature ≥ 57°C (135°F)

Critical Limit Monitoring Corrective Actions Verification Records
≥ 57°C (135°F) Digital Thermometer
If < 57°C (135°F)
Datalogger chart
Calibrate thermometer
Save chart to
computer file

*Another corrective action would be to test the pH.  If the pH ≤ 4.2; then the temperature critical limit is no longer needed.

Acidity (pH) ≤ 4.2 required for ambient storage

Critical Limit Monitoring Corrective Actions Verification Records
≤ 4.2 Digital pH meter
(bulb puree*)
If > 4.2;
(a) refrigerate or freeze,
(b) continue to ferment
Calibrate pH meter Batch log

* Puree several bulbs.  Test pH of puree.  If needed, add one-tenth volume of distilled deionized water (not tap) to help liquefy the puree.

Water activity ≤ 0.85 required for ambient storage at pH > 4.2

Critical Limit Monitoring Corrective Actions Verification Records
≤ 0.85 Digital Water activity
meter (per batch)
If > 0.85 Aw;
(a) refrigerate or freeze,
(b) hot air dry ≥ 57°C (135°F)
Calibrate water
activity meter
Batch log

bacOkay.  I have been asked many times what verifications are there that a particular fermentation culture is safe, “clean” or “pure”?  Whether its yogurt, kefir, sourdough, kombucha, buttermilk, cheese, or koji; the question remains. For the most part, natural fermentations are quite rigorous and the true culture organisms predominate.  If foodborne illness organisms get into the culture, it is likely they will not survive due to microbial competition from the culture.  However, studies of pathogens in fermentation cultures are few and far between.

About a decade ago I sent emails to about a dozen small business culture sellers and asked them what they did regarding the safety of their cultures they sell.   The answers I got back were quite impolite to anthropological, but none had any idea of the safety of their culture, its purity, or cleanliness. From the perspective of the FDA and the Food Code, culture manufacturers MUST be “inspected” or the culture would not be usable as an ingredient.  So, culture safety starts with: “Is the culture supplier an inspected facility?”  If not, stop, move on.  Ebay or other home seller marketplaces are not typically a place to find food safety.

The next question is “how does the manufacturer know the culture is “clean” or better “safe”?  As a Master Brewer, I can tell you that the moment a brewing yeast culture is contaminated, the beer will not be exactly as planned.  It could end up a total loss.  Larger culture companies understand the economics at hand and go to great lengths to ensure their cultures are clean, pure, and safe.  Most will provide a certificate of analysis including microbiological analyses.  For example a pure brewing yeast culture should have no bacteria, no coliforms, and no Staphylococcus aureus when tested.  Beer culture manufacturers will also ensure that there are no wild yeasts.  The presence of a wild yeast could make a great beer taste like a band aid.  Even the smallest culture manufacturer can send off some of their culture to a testing lab for basic microbial analysis.  But do they?

In the absence of lab data, the retail-foodservice operator could verify their culture fermentation by performing a test batch.  This is highly recommended simply because some microorganisms could die off in culture.  Acetobacter aceti is notorious for this.  For fermentations that produce high levels of acid, the acid can select for the intended culture and help eliminate spoilage and any possible pathogens.   At the same time as the acid level gets higher, more of the culture dies off.  What about back-slopping?  Back-slopping is the practice of using culture from a successful fermentation for the next fermentation.  If the current fermentation was successful in producing acids and flavors, then it is likely that the culture is “mostly” pure and a good candidate for back-slopping.  Back-slopping should be safe for a retail-foodservice operator fermenting foods using a HACCP plan, provided they provide an SOP describing where the original culture came from and how they determine the culture is maintained so that it is likely free of pathogens.

Bottom line – buy cultures from FDA or regulatory inspected manufacturers.  Ask for a certificate of microbial analysis.  Create a starter batch of product from fresh purchased cultures to see that the culture produces the intended product characteristics.  Use the “art” of fermentation to notice the nuances and slight differences that could mean the culture is not “clean and pure”.  Lastly, use excellent sanitation principles to minimize cross contamination or environmental contamination of the fermentation process. Re-use these starter cultures for as long as they demonstrate successful fermentation characteristics indicating they are “clean” and “pure”.

Large food fermentation culture companies: DSM, Danisco (including Kefir cultures), and Chr. Hansen.