Debra Wink

Pineapple juice is a simple solution to a problem that many people encounter while trying to start a sourdough seed culture from scratch. Oftentimes, a new culture will appear to start off very strong, only to die a day or two later. The early expansion is caused by a prolific gas-producing bacterium which many mistake for yeast. Pineapple juice can be added to flour instead of water at the beginning, to insure against unwanted bacteria and the problems they leave in their wake. It doesn't change the end result, but it does seem to keep things on the track to finish on time. Part 1 tells the story of where the pineapple remedy comes from and how it was conceived. The rest of the story probes deeper into how it all works. But first, here is a recap of the key patterns revealed by notes and data collected during experimental trials:

• When starters expanded significantly on the second day, a period of stillness followed, and the appearance of yeast was delayed.


• Gas-producing bacteria stopped growing when the pH dropped to 4.5, but yeast growth didn't begin until the pH fell to around 3.5, accounting for the period of stillness.


• Lowering the pH in the initial mixture, by adding ascorbic acid or by replacing the water with pineapple juice, kept gas-producing bacteria from growing and brought about a more timely and predictable result.

But it wasn't enough just to find a fix. The problem-solving efforts of my team were creating a buzz which we hadn't anticipated and this thing, like the seed cultures we were creating, was taking on a life of its own. Some were jumping to premature conclusions, and speculation seemed to be spreading as fact. It made me very uncomfortable, because I'd rather be dispelling myths than adding to them. I wanted to find some real answers, and find them fast, so I started making phone calls. I found two local labs that could help me out. One had the capability to identify leuconostocs, and the other to detect lactobacilli and other bacteria of interest. I submitted samples of a day two starter during the big expansion. Both labs found that there were three organisms growing. But there were no lactobacilli or yeasts found, which supports what I observed time after time on microscopic examination. My gas-producer was identified as Leuconostoc citreum. At the time, I couldn't find much information specific to this organism, although it seems to share many characteristics with other Leuconostoc species found in foods. Most will not grow below pH 4.8, and this one doesn't appear to be an exception.

Until recently, I could only theorize that the Leuconostoc may actively hinder the process, because the pattern supports it, and because it's not uncommon for microorganisms to produce substances which inhibit competitors. But in updating this article, a new search of the scientific literature finally uncovered the piece of the puzzle I was looking for. Who would have thought the answers would be found in kimchi and sake? It turns out that kimchi fermentation has a lot in common with sourdough development, and mirrors the early days of the seed culture process. Leuconostoc citreum plays a dominant role in the early and mid-phases of fermentation where it causes a slow and prolonged drop in pH, and retards the growth of other lactic acid bacteria.[1] In a study on sake fermentation, Leuconostoc citreum was found to produce bacteriocins (bacterially-produced antibiotic proteins) which inhibit the growth of similar lactic acid bacteria (i.e., lactobacilli).[2] It appears that these bacteriocins linger for a time even after the organism stops growing, although their effect is diluted through successive feeding. A dosage effect would explain nicely the apparent relationship between the vigor with which this bacterium flairs up initially, and the number of days the starter remains still afterward. The higher the rise, the longer it seems to take to recover.

In addition to Leuconostoc citreum, there was also a large amount of Aerococcus viridans. The first lab I visited found Leuconostoc to be in the greatest quantity, but Aerococcus was multiplying so fast that it soon passed the Leuconostoc in number. That is important, and could very well have contributed to the delayed progress. Even though Aerococcus doesn't produce gas, and so was not responsible for any of the expansion, it is not an acid producer either. So while it was using up a large share of the available sugars, it was not helping the pH to fall. Aerococcus is an occasional spoilage organism in unpasteurized milk, which is the extent of information that I have found on its involvement in foods. Its lower limit is not given in my reference books, but since pineapple juice seems to keep it at bay, I suspect that it must be in the same ballpark with leuconostocs. I'm still not sure how big a part each of these organisms plays in slowing the progress of a seed culture, but lowering the pH at the outset seems to be a blanket fix.

I mentioned in Part 1 that some of the bacteria were flipping, twirling and zipping around under the microscope. Those were Enterobacter cloacae. Enterobacter produces gas, but since it was present in only a scant amount compared to the others, I think it safe to say that the Leuconostoc was responsible for the majority of it. However, Enterobacter contributes to an unpleasant odor, as do Aerococcus and Leuconostoc. Because some people report a very stinky smell and others not as much, I'd have to say that even among starters that grow Leuconostoc, not all necessarily have the same combination of bacteria. There are others that can grow as well. Results vary from flour to flour and year to year, because the number and species of microorganisms are influenced by conditions relating to weather and grain crop production.[3] I wish I could have all the organisms identified at every stage, but there aren't any laboratories in my area that are equipped to identify wild yeasts or sourdough bacteria. And even if they could, the cost would be prohibitive. I was fortunate to be in a position to have two of the organisms identified as a professional courtesy.

With the additional information, and having watched the drama unfold under the microscope, I started seeing the seed culture process not as good guys out-competing bad or gradually increasing in number, but as a natural succession of microorganisms that pave the way for "the good guys" in the way that they transform their environment. There are bacteria in flour that prefer the more neutral pH of freshly mixed flour and water (like Leuconostoc and company). They are the first to start growing, some producing acids as by-products. This lowers the pH, and other bacteria begin to grow; they produce their acids, lowering the pH even more. It soon becomes too acidic for the first batch and they stop growing. One group slows down and drops out as the next is picking up and taking off. Each has its time, and each lays the groundwork for the next. It's much more like a relay than a microbial free-for-all. The baton is passed to the next group in line as conditions become suitable for them. The acidity increases a bit more with each pass, and the more acid-loving bacteria can eventually take over. The appearance of yeast seems to be tied in some way to low pH---maybe directly, maybe indirectly, but the correlation shows that it isn't random in the way that "catching" yeast from the air would be, or their gradually increasing in number.

In the late fall/early winter of 2004, I was coaching a group of women on Cookstalk, Taunton's Fine Cooking forum, and I noticed something else. My starters sort of liquefy the day before yeast starts to grow. Gluten disappears, which shows the work of proteolytic enzymes. At first I thought it signaled the appearance of lactobacilli and their proteases. But now I think it was simply an indicator that the pH had dropped low enough to activate aspartic proteinase, a pH-sensitive enzyme abundant in wheat.[4] Because I prefer to seed a new culture with whole grain flour for at least three days, there are more cereal enzymes present than in a starter fed with white flour (most of them are removed with bran in the milling process). But either way, it is a good sign of Lactobacillus activity, whether by production of bacterial proteases or by the organism's effect on pH and activation of cereal proteases.

The starters were developing a little more slowly this time around, which inspired me to describe the different stages that a new culture transitions through, rather than try and pin it to a time frame. Room temperature is different from one kitchen to the next, as well as season to season. Sometimes rye flour works faster, sometimes whole wheat is faster. Sometimes a culture doesn't start producing its own acid for the first two days instead of one. Because this process involves variable live cultures under variable conditions, it doesn't always work in a prescribed number of days, but it follows a predictable pattern. While this has been a discovery process for me, it is not a new discovery:

"There has been nice work done in Rudi Vogel's lab on the microflora of a freshly started sourdough: first, there are enterobacteria (Escherichia coli, Salmonella, Enterobacter), highly undesirable organisms that stink terribly. Then there are homofermentative lactobacilli (good lactic acid producers, but they don't produce gas or acetic acid), then acid-tolerant, heterofermentative lactobacilli that make lactic and acetic acid, as well as CO2. I think this took about forty-eight hours at 30ºC in Vogel's study. The stink at the beginning does not matter as the organisms will be diluted out or die eventually. No L. sanfranciscensis appears by forty-eight hours, though: these will occur only after repeated refreshments. Peter Stolz told me that it takes about two weeks of repeated inoculations to get a good 'sanfranciscensis' sourdough."[5]

That paragraph didn't have any special significance for me until I had gotten to this point. But when I read it again, I had one of those aha moments. Not only did this describe a succession, but it filled in some of the blanks, and I could see clearly how all these microorganisms related to the four phases I had defined. Here is the updated version marrying the two. You don't need a microscope for this, because there are outward signs which serve as useful indicators of progress.

The First Phase:
For the first day or so, nothing really happens that is detectable to the human senses. It doesn't taste any tangier or develop bubbles. It remains looking much the same as when it was mixed, except a little lighter in color if an acid was used, and a little darker if not. While nothing appears to be happening, the first wave of bacteria (determined by pH and the microflora in the flour) are waking up, sensing their new environment and preparing to grow. This phase usually lasts about one day, sometimes two.

The Second Phase:
The starter will begin producing its own acid and develop a tangy taste (although it might be difficult to distinguish from pineapple juice). Lactic acid bacteria are actively growing at this point. When using only water, this phase represents two waves of microbes---first Leuconostoc and associates, followed by homofermentative lactobacilli and possibly other lactic acid bacteria. By controlling the pH, you can by-pass the leuconostocs and other "highly undesirable organisms that stink terribly," and skip to the second wave. It will get bubbly and expand only if the pH is not low enough to prevent growth of gassy bacteria, otherwise there won't be much else to see. There probably won't be much gluten degradation, and it may smell a little different, but it shouldn't smell particularly foul unless started with plain water. This phase can last one to three days or more. If it is going to get hung up anywhere, this is the place it usually happens, especially if it is put on a white flour diet too soon. If after three days in this phase, it still doesn't become more sour and show signs of progress, the best thing to do is switch back to whole grain flour for one or more feedings. Whole grain flour has a much higher microbial count and will re-seed the culture and get it moving again.

The Third Phase:
The starter will become very tart---an indication of more acid production by more acid-tolerant bacteria. The gluten may disappear and tiny bubbles become more noticeable. These are signs that heterofermentative lactobacilli have picked up the baton. Once a starter becomes really sour, it usually transitions right into phase four. Note that lactic acid doesn't have much, if any aroma, and so smell is not a very reliable way to judge the level of sourness.

The Fourth Phase:
Yeast start to grow and populate the starter relatively quickly at this point. It will expand with gas bubbles all over and begin to take on the yeasty smell of bread or beer.

This pattern suggests that wild yeasts are activated by low pH. Or perhaps the activator is something else produced by lactobacilli, but it happens predictably at this point for me, as long as the whole grain flour has not been diluted out. There may be some variation among wild yeasts as to the exact pH or activating substance. I have been unable to find the answer in scientific literature, and my contact at Lallemand did not know. I have only found studies done with cultivated strains of Saccharomyces cerevisiae, which don't seem to require much more than a fermentable sugar (and may explain why seed cultures take off much quicker in a bakery environment where baker's yeast is everywhere). The most useful information I have found on the subject is this, about microbial spores in general:

"Although spores are metabolically dormant and can remain in this state for many years, if given the proper stimulus they can return to active metabolism within minutes through the process of spore germination. A spore population will often initiate germination more rapidly and completely if activated prior to addition of a germinant. However, the requirement for activation varies widely among spores of different species. A number of agents cause spore activation, including low pH and many chemicals... The initiation of spore germination in different species can be triggered by a wide variety of compounds, including nucleosides, amino acids, sugars, salts, DPA, and long-chain alkylamines, although within a species the requirements are more specific. The precise mechanism whereby these compounds trigger spore germination is not clear."[6]

What this means is that for dormant cells to return to active growth (germinate), they need to break dormancy (activate) which is initiated by different things for different species. In the case of these wild sourdough yeasts, if all they needed were food or oxygen, which are there from the get-go, then they would start growing immediately. The fact that they don't, is probably why many people think they need to be caught from the air, or that large quantities of flour must be used to round up enough of them. There are enough dormant cells present even in relatively small quantities of whole grain flour, but it's like a game of Simon Says. You can try to coax them into growing, with food and all the things you may fancy to be good for actively growing yeast. But they're not active. They are dormant, and will remain so until they receive the right message from their surroundings. Compare this to the plant seed that sits in soil all winter long, waiting until spring to sprout, when conditions are most favorable. Is it a survival mechanism? I don't know, but waiting for the pH to drop does increase the likelihood that the yeast will wake up in the company of lactobacilli, with which they seem to share a complex and mutually beneficial relationship. It is also important to point out here that active sourdough yeasts thrive in a much wider pH range than what appears to be required for activation of dormant cells. The point to keep in mind is that active and dormant cells are physiologically and metabolically different, which also means their needs are different.

This pattern of growth is not unique to the formula in the Bread Baker's Apprentice. I have seen the same progression, in whole or in part, with all the starter formulas I've tried. And it doesn't really matter how much flour you start with. In fact this can be done with very small quantities of flour. All else being equal, it proceeds just as fast with a teaspoon as it does with a pound. Procedures that call for two or three feedings per day, or large refreshments before yeast are active, can actually get in the way of the process. Overfeeding unnecessarily dilutes the acid, which slows the drop in pH, and keeps it from moving through the succession of microorganisms in the timeliest manner. But while it can take up to two weeks or more this way, with Mother Nature as the driving force, things do fall in line eventually. It's just a question of when. Three to five days is about all it really takes to reach the yeast activation stage at average room temperature, somewhat longer if Leuconostoc and associates grow. The strategy is quite different from reviving a neglected starter, which is likely to have an overabundance of acid, and a large population of yeast and sourdough bacteria, however sluggish they may be.

So, what can we do instead to facilitate the process? Start by providing conditions for the first two to three days which are favorable to lactic acid bacteria. A warm spot if you can easily manage one (but not too much higher than 80ºF), and a reasonably high hydration (at least 100%). Use pineapple juice if you like, to bypass the first round of bacteria. Feed with whole grain flour until yeast are actively growing, not for the wider spectrum of sugars it may offer, but for its higher numbers of yeast and lactic acid bacteria to seed each phase in its turn. Don't feed too much or too frequently, so as to allow the acids to accumulate and the pH to fall more rapidly. The ideal feeding quantity and frequency would depend on the temperature, hydration, and how fast the pH is falling. However, I usually recommend once a day at room temperature, simply because it is the easiest to manage, it works, and the daily manipulation helps to keep mold from getting started. Mold is the biggest stumbling block for procedures in which a young mixture is allowed to sit idle for two or three days at a time. Turning surface mold spores into the center by re-kneading or stirring and scraping down the sides daily, is the best way to get around it. Mold is not inhibited by low pH or pineapple juice, and anti-mold properties don't fully develop until sourdough is well established.

While you don't actually need a formula to do this, no article on making sourdough starter would be complete without one. This procedure was designed with simplicity in mind, to be efficient and minimize waste. It was developed with the participation of four willing and very patient women whom I worked with online---DJ Anderson, Karen Rolfe, Deanna Schneider and the still-anonymous 'lorian,' whose plea for help is what renewed the quest to find a better way. I learned a great deal from the feedback they gave me as we worked out the kinks, and this formula is a tribute to them.

There is nothing magic about the two tablespoons of measure used throughout the first three days. Equal weights didn't provide a high enough ratio of acid to flour to suit me, and equal volumes did. Two tablespoons is enough to mix easily without being overly wasteful (and just happens to be the volume of an eighth-cup coffee scoop, which is what I kept on the counter next to the flour and seed culture for quick, easy feeding). These first few days don't really benefit from being particularly fussy with odd or precise measuring, so make it easy on yourself. Keep it simple, and let Mother Nature do the rest.

Day 1: mix...
2 tablespoons whole grain flour* (wheat or rye)
2 tablespoons pineapple juice, orange juice, or apple cider

Day 2: add...
2 tablespoons whole grain flour*
2 tablespoons juice or cider

Day 3: add...
2 tablespoons whole grain flour*
2 tablespoons juice or cider

Day 4: (and once daily until it starts to expand and smell yeasty), mix . . .
2 oz. of the starter (1/4 cup after stirring down-discard the rest)
1 oz. flour** (scant 1/4 cup)
1 oz. water (2 tablespoons)

* Organic is not a requirement, nor does it need to be freshly ground.

** You can feed the starter/seed culture whatever you would like at this point. White flour, either bread or a strong unbleached all-purpose like King Arthur or a Canadian brand will turn it into a general-purpose white sourdough starter. Feed it rye flour if you want a rye sour, or whole wheat, if you want to make 100% whole wheat breads. If you're new to sourdough, a white starter is probably the best place to start.

On average, yeast begin to grow on day 3 or 4 in the warmer months, and on day 4 or 5 during colder times of the year, but results vary by circumstance. Feed once a day, taking care not to leave mold-promoting residue clinging to the sides or lid of your bowl or container, and refer back to the different phases to track progress. Once you have yeast growing (but not before), you can and should gradually step up the feeding to two or three times a day, and/or give it bigger refreshments. This is the point at which I generally defer to the sourdough experts. There are several good books on sourdough which address the topic of starter maintenance and how to use it in bread. Just keep in mind that the first days of the seed culture process have nothing to do with developing flavor or even fostering the most desirable species. The object is simply to move through the succession and get the starter up and running. The fine-tuning begins there. Once yeast are growing well, choose the hydration, temperature and feeding routine that suits you, and the populations will shift in response to the flour and conditions that you set up for maintenance.

One more thing I have found is that with regular feeding at room temperature, new starters seem to improve and get more fragrant right around the two week mark. Maybe this coincides with the appearance of Lactobacillus sanfranciscensis mentioned previously. It is generally regarded as the most desirable species, as well as the one found to be the most common in traditional sourdough.[7] A Fifth Phase? Obviously, there is still more to learn.   -Debra Wink

References

1. Choi, In-Kwon, Seok-Ho  Jung, Bong-Joon Kim, Sae-Young Park, Jeongho Kim, and Hong-Ui Han. 2003. Novel Leuconostoc citreum starter culture system for the fermentation of kimchi, a fermented cabbage product. Antonie van Leeuwenhoek  84:247-253.

2. Kurose, N., T. Asano, S. Kawakita, and S. Tarumi. 2004. Isolation and characterization of psychotrophic Leuconostoc citreum isolated from rice koji. Seibutsu-kogaku Kaishi 82:183-190.

3. Doyle, Michael P., Larry R. Beuchat, and Thomas J. Montville. 2001. Fruits, Vegetables, and Grains, p. 135. Food Microbiology Fundamentals and Frontiers, 2nd ed. American Society for Microbiology Press, Washington, DC.

4. Katina, Kati. 2005. Sourdough: a tool for the improved flavour, texture and shelf-life of wheat bread, p. 23.VTT Technical Research Centre of Finland.

5. Wing, Daniel, and Alan Scott. 1999. Baker's Resource: Sourdough Microbiology, p. 231. The bread Builders. Chelsea Green Publishing Company, White River Junction, VT.

6. Doyle, Michael P., Larry R. Beuchat, and Thomas J. Montville. 2001. Spores and Their Significance, p. 50. Food Microbiology Fundamentals and Frontiers, 2nd ed. American Society for Microbiology Press, Washington, DC.

7. Arendt, Elke K., Liam A.M. Ryan, and Fabio Dal Bello. 2007. Impact of sourdough on the texture of bread. Food Microbiology 24:165-174.

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This article was first published in Bread Lines, a publication of The Bread Bakers Guild of America.
Vol. 16, Issue 2, June 2008.

Related Links:
  The Pineapple Juice Solution, Part 1 | The Fresh Loaf
  Lactic Acid Fermentation in Sourdough | The Fresh Loaf 
  Basic Procedure for Making Sourdough Starter | Cooks Talk

You know what they say... Life is a journey. But have you ever been pulled down a path that you otherwise would have walked on by? That's what happened to me when I started playing with sourdough. I didn't even like sourdough, or so I thought until about seven and a half years ago. I was watching the food network one day, and Daniel Leader appeared as a guest on Cooking Live. He was demonstrating how to make a sourdough starter from nothing but flour and water. How fascinating! I had no idea you could do that. Bread science was nowhere in the curriculum when I went to university almost 30 years ago, let alone sourdough. But for someone with a microbiology degree and a passion for baking, sourdough is the perfect marriage of two loves. I had to try it for myself. And so began the journey. The path so far has taken some surprising twists and turns, and led to meeting many interesting people along the way. Including Peter Reinhart, who has been nothing but gracious and supportive throughout, and who is ultimately responsible for getting me to sit down and record this story in my own words. Now, back to the beginning...

In early 2002, I was a member of the King Arthur Baking Circle, a message board for baking enthusiasts. With this brand new interest in sourdough, I found myself reading all of the threads under that category. In March another member, Pat Doucette began posting of the difficulties she was having in getting a starter going. She had tried a few different recipes with no success. Now she was following the formula in The Bread Baker's Apprentice and... still no luck. Newly armed with all of the advice that she was getting from others on the forum, she started over. And once again, she got results that were nothing like the book describes. But a pattern was becoming clear. On the second day, her seed cultures would fill with bubbles and expand to over three times the starting volume when minimal growth was expected. And then do nothing on the third and fourth days when they were supposed to be expanding more and more. They came on strong and then died at the same point each time. A pattern holds a clue, so I offered to do the procedure myself and see if I could reproduce what she was seeing. I followed the directions to the letter and, lo and behold, my results duplicated Pat's perfectly. I may be the only person on the planet who would be excited about this, but it gave me something to study and troubleshoot. There was something unexpected going on at the microbial level. Living things are funny that way, and microorganisms don't always follow directions.

One by one, other people on the message board began to speak up and post that they had experienced the same thing. In fact, it seemed that many more saw that scenario than the one described in the book. This phenomenon had nothing to do with local strains of lactobacilli and yeast as some had surmised, because Pat was making starter in Massachusetts and I was in Missouri. Others chiming in represented various regions of the country from coast to coast. This pattern is apparently quite common. We ran the gamut of theories on why yeast were coming on like gangbusters, only to quit and become non-responsive. We tested each theory by trying different flours at various points, increasing the feeding frequency, changing the hydration and water source, cooling it down, and anything else that anyone thought might help. But in the end, nothing fixed the problem, and the results weren't making much sense to me.

At that point, I had to do what microbiologists do when things don't add up---go back to the microscope and take a look. That meant packing up my starters, taking them to work, and having to answer all the curious questions about what I was doing and why. But the microscope answered a few of my questions, and that day proved to be the turning point. No wonder things didn't make any sense! We were operating on the assumption that we were growing yeast. What I found was that there were no yeast or lactobacilli to be seen anywhere in all the activity of day two. Not a single one. But it was like a three-ring circus in there---different kinds of bacteria, some round, some rod-shaped, some motile, some not. Some were spinning, some were twirling, some flipping or zigzagging, and some were just darting back and forth across the field. What were these bacteria, and which one was responsible for all the gas?

I knew, from having made so many starters by now, that this pattern does turn into sourdough if given more time. So, I looked at cultures each day in the process, comparing them to my established starter which was yeasty and stable. Everything quiets down in there and yeast emerges a few to several days later. They don't appear to be coming from the air as many people believe, because it happens even in a covered container. But if they are already in the flour as the more reliable sources say, then why couldn't I find any? Obviously, there was more to this than just a symbiotic relationship between lactobacilli and yeast gradually increasing in number, good guys out-competing bad---the usual explanation. It was evident that there are many more bacterial and fungal species present in flour than just sourdough lactobacilli and yeast. But where were the good guys? Why weren't they growing? It was time to close the cookbooks and open the textbooks.

I turned to a large, newly updated food microbiology tome, and was disappointed to find only two brief paragraphs on sourdough, and not much more on yeasted breads. So it became a challenge to find the information, mostly borrowed from chapters on wine, beer, dairy, and other food fermentations that share something in common with sourdough. I was able to narrow down the gas producer to a Leuconostoc species. The tip-off was reading that almost 90% of spoiled doughs are caused by Leuconostoc mesenteroides or Leuconostoc dextranicum. When I started searching for more on the genus, I found Leuconostoc mesenteroides is considered the primary agent in the fermentation of an Indian steamed bread called idli. (Spoilage is a subjective thing from culture to culture.) After soaking grains for a day and then grinding them with water into a paste, there is a 15-24 hour fermentation during which the idli batter increases in volume by about one and one half to three times---the same as our wild day two growth.

Leuconostocs are also occasional spoilage bacteria in wine making, "but they undergo little or no growth during the alcoholic fermentation and tend to die off because of competition from yeasts. Nevertheless, these bacteria are capable of abundant growth in the juice and, if yeast growth is delayed, they could grow and spoil the juice or cause stuck alcoholic fermentation."[1] Many microorganisms produce characteristic aroma compounds, and so smell is also an important clue. I had previously described an unamended, all-white seed culture as smelling like sour milk with a hint of rotten cheese. Then I learned that some leuconostocs are added to dairy fermentations (such as cultured buttermilk, and cheeses like Gouda, Edam, blue cheese and havarti) for their carbon dioxide and aroma compounds. Together, these pieces all fit what we were seeing, and according to the chapter on fermented vegetables, leuconostocs are quite common in nature and found routinely on all kinds of produce and plant material. So, we can expect them to be present on grains and in flour.

Knowing how bland a flour-water mixture starts out, and seeing how the microscopic picture becomes more subdued as the sourness increases, it was apparent that the shift in populations and activity are tied to changes in acidity. pH is a fundamental factor in microbial growth. Some like it neutral while others need more acidity or alkalinity, but each species has its own pH range. The reason that the starters had become quiet on day three was because the pH had fallen and the gas-producing bacteria were no longer growing. Even though I still wasn't sure what these bacteria were, it was clear that whenever the gas-producing one or ones grew, the starter would subsequently become still and take longer to finish---sometimes by several days. I reasoned that the best solution might simply be to keep them from growing. And since they stop growing as the pH drops, why not add an acidic ingredient to the mixture to lower the pH and inhibit them from the outset?

It was May now and Evan Shack had entered the picture. Unaware that this was already a hot topic, he began posting to the message board seeking help after having just tried to make starter and getting the same result that we had. Evan was interested in learning the science behind it, and he and Pat were both eager to get to the bottom of the problem, so they volunteered to do some testing. Soon after we joined forces, Gary Wray contacted me and we invited him to join our little task team. With so many different recipes to choose from, it was clear that there are several approaches to making starter. But we needed to pick a direction to focus our problem-solving efforts. And because so many people on the message board were loyal fans of The Bread Baker's Apprentice, the group decided the goal would be to use that formula, altering it as little as possible, and make it proceed as described in the book. The fix should be simple, with ingredients readily available at home or in the average grocery store. Our choices for the acids were ascorbic (vitamin C), citric (sour salt), tartaric (cream of tartar), acetic (vinegar), lactic (yogurt), and mixed acids (fruit juices).

For our first trial we chose ascorbic acid, because it is readily available in the vitamin supplement section, known to be beneficial, and widely accepted in bread-making. Pat and I used vitamin C tablets that we had on hand. We crushed them and mixed the powder with the flour and water on day one. And much to our amazement... it worked! No gassy bacteria, and we were both growing yeast on or before day four, where it had been taking about seven days. But I discovered a little problem with supplement pills, which is that some are buffered without being labeled as such. I was not getting the pH to drop in mine even though I kept adding more and more vitamin C. When I took a closer look at the bottle, I found two ingredients listed which together, formed a buffer system that was keeping me from reaching the pH I was aiming for. Pat's vitamin C was not buffered and her starter took off in only three days.

Buffer problems aside, neither one of us enjoyed the task of crushing pills. And whirring them in a blender with the water only worked so-so. We also had no idea what the best dose would be. Gary and I both had ascorbic acid powder, so we did another experiment testing different doses ranging from 1/8 to over 1 teaspoon mixed with the 4.25 ounces of flour on day one. It was a fun experiment to do. With the jars lined up next to one another, they looked like perfect stair steps as the starters began to rise. It was easy to see which doses were most effective by how fast and how high the cultures rose. For me, the most active jars were the ones with 1/4 and 1/2 teaspoon of ascorbic acid powder. For Gary, the best results came from 1/2 and 3/4 teaspoon, and so we settled on 1/2 teaspoon as the recommended dose. While the ascorbic acid worked quite well, and may be the ingredient of choice for purists or professionals, the average person must go a little out of their way to find or mail-order it. So we decided to press on.

All of the acids that we tried, inhibited the gassy bacteria effectively, but sour salt (sometimes found with canning supplies) was so strong that it was hard to measure the tiny amounts accurately. Cream of tartar (found in the spice section) was too weak, and required an impractical amount to effectively lower the pH. We dismissed lactic acid because we didn't want to deal with dairy or go to the trouble of draining yogurt for the whey. And vinegar was so highly inhibitory to yeast in the doses required to lower the pH, that it was no solution at all. That left fruit juices. I tested the pH of various juices and made a list for the group to try---apple cider, orange, lemon, grapefruit and pineapple juices seemed like the most suitable candidates based on wide availability. But whenever trying a new juice or acid, I had the group run a negative control alongside---a duplicate to the test in every way, except using plain water. This would show whether changes in the result were due to the ingredients under evaluation, or to chance or variation in experimental conditions. Time after time though, the control jars followed the familiar pattern, while the test jars proceeded by the book.

While the trials were under way I went back to basics, monitoring the changes in acidity and examining seed cultures under the microscope every day. I recorded pH readings, growth measurements and observations at the beginning and end of each 24-hour feeding cycle. After a number of runs, I gathered my notes to compare and look for patterns. (My pH paper was only sensitive to the nearest 0.5 increment, so readings are approximate.) I found that when I acidified the day one mix to 4.5, it stayed at 4.5 until I fed it again on day two. If I didn't add more acid at that time, the freshly fed starter would read 5 and the gassy bacteria grew on day two and followed the oh-so-familiar pattern. If I acidified the day one mix to 4, it stayed at 4 until I fed it on day two, after which it read 4.5. The gassy bacteria did not grow and the culture started producing its own acid as other lactic acid bacteria were increasing in activity. During the second 24 hours, the pH dropped to 3.5 and the starter tasted really sour. Yeast usually appeared the day after. When I acidified the day one mix to 3.5, I actually got some yeast growth on day two. I'm not sure that this is the best way to go, though. I've only done it once with citric acid and yeast were not as vigorous the next day as I had hoped to see them. More testing could be done. But the key points here are that the gassy bacteria grew at or above pH 5, not at or below 4.5, and the cultures I was growing all failed to produce acid of their own in the first 24 hours. That is important because a day one flour-water paste measures about 6---quite inviting to leuconostocs. And even more importantly, in all my trials I have never seen yeast before a starter gets sour, but it usually follows very soon after.

I was hoping orange juice would perform well, since it is a good source of Vitamin C and a staple in many homes. But, it turned out not to be acidic enough to meet the group's objective, which was to use it only on the first day. However, Orange juice and apple cider do work well if they are used in place of the water for two or three days. Pat was the first to try pineapple juice, which has a lower pH than most other juices, and just happens to come in handy 6-oz cans (exactly the right measure for day one). She liked it so well that she stopped testing anything else and started recommending it to others. Almost everyone who tried it was thrilled with the results, and so pineapple juice became the solution that stuck. While the group's mission was accomplished, the story doesn't end here. But the rest will have to wait until next time, so please stay tuned...

References
1. Doyle, Michael P., Larry R. Beuchat, and Thomas J. Montville. 2001. Food Microbiology Fundamentals and Frontiers, 2nd ed. American Society for Microbiology Press, Wahington, DC.

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This article was first published in Bread Lines, a publication of The Bread Bakers Guild of America.
Vol. 16, Issue 1, March 2008

The Pineapple Juice Solution, Part 2 | The Fresh Loaf