After 7 days of feeding my sour dough starter “took off” and was ready for baking. Even with a water bath set to 28 °C it took longer than expected. I started off with 100% hydration as this is convenient when you have to feed your starter frequently. Using only whole grain rye flour and water, I fed my starter every 12 hours (I’ve included details of the “feeding schedule” at the end of this post). This time interval is based on the growth cycle of yeast, where the yeast after an exponential growth phase reaches a plateau after 8-12 hours. This is the best time for feeding the starter.

There seems to be a consensus that a wet starter (i.e. 100% hydration) favors growth of lactic acid bacteria (LAB) which in turn produce acids. The low pH after 2 days in my starter suggests plenty of LAB activity, so the main challenge for me was to get the yeast growing. Considering the fact that the yeasts found in sourdoughs prefer areob conditions for growth, I should have whisked in more air with each addition of water. And I wonder if this is the origin of the widespread myth that you “catch wild yeasts from the air”. I’m quite sure whisking helps, but what you do is not to catch yeast, but rather feed oxygen to your starter. This needs testing though! Most starter recipes call for discarding of half or even more of the starter before each feeding. Even though it seems wasteful I wonder if an important effect of this is to dilute the acid produced by the LAB (the flour may also act as a buffer). This acid will to some extent slow the growth of yeasts (even though the sourdough yeasts are far more acid tolerant than the conventional brewer/baker’s yeast Saccharomyces cerevisia).

Bubbles indicating that the starter is active

Regarding temperature the growth optimum for LAB lies around 32-33 °C whereas the growth optimum for yeast is somewhat lower at 28 °C. The sourdough FAQ has further temperature recommendations which are illustarted in the graph below (data from sourdough FAQ). Holding this together with the notion (see for instance p. 272 in “The handbook of dough fermentations”) that lower temperatures (20-25 °C) favor acetic acid production (= stronger flavor) and higher temperature (> 32 °C) favors lactic acid production (= milder flavor) it immediately becomes clear why a starter kept at roomtemperature has little yeast activity and smells of acetic acid. It need not be ruined, but is desperately in need of dilution, aeration and higher temperature.

Effect of temperature on growth of lactic acid bacteria and yeast based on data for optimum growth and no growth from the sourdough FAQ

I’ve kept the starter alive since August and baked with it at least once a week. I make sure that I keep 50-100 g which I store in the fridge. I’ve also frozen a sample just in case. I’ve changed from 100% hydration to 67% hydration, as this simplifies the calculations a little. On the evening before baking day I feed the starter to a total starter weight of approximately 900 g. The next day I bake bread as follows (the exact numbers were calculated using an internet sour dough calculator with the following input: 3200 g total dough weight, 25% starter, 67% hydration of starter and final dough and 1.8% salt):

Sour dough bread
949 g water
1417 g flour *
800 g starter (67% hydration, 25% of total dough)
34 g salt

* for instance 300 g rye whole grain, 200 g rye fine, 300 g whole grain wheat and then plain all-purpose wheat flour up to 1417 g.

Mix water and flour mixed until all flour is wetted. Leave for 15-20 minutes (during which the autolyse proceeds – this eases subsequent mixing). Mix (see more comments below regarding method/machine for this) until dough is smooth, and while mixer is running add sour dough starter. Once the starter has been properly incorporated into the dough, add the salt. Cover and leave to rise until volume has increased 30-100% (I know – this is not very accurate…). I have left it in on my bench top, but while this worked well on warm August days, it seems to be less than ideal on colder October days. Leaving the dough to rise on top of the fridge might be a conventient compromise here as my current waterbath is not large enough to hold the mixing bowl with dough. The reason I use a starter with a 67% hydration is that I can be more sloppy when adding the starter to the sourdough as it will not change the hydration of the dough. After proofing and slashing I bake the breads on a baking stone which is preheated to 250 °C. Right beneath the baking stone I have a small oven proof dish that I fill with boiling water. This helps to moisten the air in the oven and it simulates the steam injection port of professional baking ovens. There are several reasons why this is important. Moist air is a better heat conductor than dry air, and it prevents the surface from drying out too early while baking, resulting in a better oven spring. Furthermore the moist air condenses on the cold surface of the dough which improves gelatinization of the starch. This in turn gives better crust formation. After 10 min at 250 °C I open the oven to let the moisture out, take out the dish with water, turn the heat down to 220 °C and close the oven door. I bake the breads to a core temperature of about 93-95 °C.

Here I bake two 800 g loaves on a baking stone. Notice the dish with water for steam generation.

I should comment on mixing. When kneading by hand I’ve had a tendency to add to much flour. In fact I think this is one of the reasons why I quit baking bread several years ago – I found that the breads I made generally were a little to dry with a poor crumb, and at that time I didn’t really sit down and think about these matters. In retrospect however there’s no doubt that baking bread and adding flour ad lib until the dough feels good to touch is NOT recommended. Well anayway not unless you stop adding flour while the dough is still quite sticky. The thing about doughs with a high percentage rye is that they are quite sticky, and they should be. This is the best argument you’ll ever get for buying a kitchen gadget: bread doughs are too sticky to be kneaded by hand! There you have it! I’ve settled with the Assistent from Sweden. It was formerly sold under the Electrolux brand, but is now marketed indepentendly, yet it is still produced at the very same factory as always. In the US the machine is known as the Magic Mill. It has a huge 7 L bowl that rotates. The roller is attached to a flexible arm, so if the dough is to hard to work the arm just moves to the middle of the bowl. This significantly reduces the chances of overheating the motor. There are of course other alternatives from Kitchen Aid, Hamilton Beach and Viking Range which seem robust, but I have no experience with these. However, I doubt that the average Kenwood can cope with more than 3 kg of bread dough (but please correct me if I’m wrong ).

Unlike most other machines, the bowl of the Magic Mill/Assitent rotates while the roller pushes the dough to the sides of the bowl

Sources for further reading

I’ve read quite a bit about sourdoughs, and what I’ve been looking for a simple correlation between temperature, hydration and fermentation time. An excellent source of information with lots of practical advice is the FAQ from rec.food.sourdough.

I think the best resource I’ve found sofar is Lorenz and Bruemmer’s chapter “Preferments and Sourdoughs for German Breads” and Teija-Tuula Valjakka, Heikki Kerojoki and Kati Katina’s chapter “Sourdough Bread in Finland and Eastern Europe” in “The handbook of dough fermentations”. I will have to study these more carefuly.

There are quite a number of academic publications which also touch upon the effect of temperature on acid development. Here are some snippets:

“Controlled production of acetic acid in wheat sour doughs”:

…temperature has no significant effect, and that fructose is more efficient in influencing the FQ than dough yield.

FQ = fermentation quotient = lactic acid / acetic acid

“Volatile compound and organic acid productions by mixed wheat sour dough starters: Influence of fermentation parameters and dynamics during baking”:

… Low temperature (25 degrees C) and sour dough firmness (dough yield 135) were appropriate for LAB souring activities but limited yeast metabolism. Raising the temperature to 30 degrees C and semi-fluid sour doughs gave more complete volatile profiles …

“Sourdough: a tool for the improved flavour, texture and shelf-life of wheat bread” (Ph.D. thesis of Kati Katina):

The production of acids depends also on other things such as fermentation temperature, time and dough yield. Optimum temperatures for the growth of lactobacilli are 30-40 °C depending on strain (Stanier et al. 1987) and for yeasts 25-27 °C. In general, a higher temperature, a higher water content of sourdough and the utilisation of wholemeal flour enhances the production of acids in wheat sourdoughs (Brummer and Lorenz 1991, Lorenz and Brummer 2003).

I must admit that I’m a little confused as some of these snippets seem to contradict. It might be that I’m overlooking something important though and that I’m taking results out of their context. Any insight from my readers on this will be greatly appreciated!

Starter details
Here’s the details from my notebook on how I fed my sourdough starter. As I mentioned above, I wonder if discarding dough in the process actually does make sense after all.

• July 29, evening: 50 g rye + 50 g water
• July 30, morning: 25 g rye + 25 g water, evening: small bubbles (!), 50 g rye + 50 g water
• July 31, morning: 50 g rye + 50 g water, evening: pH measured to 3-4 with strips, fed with 50 g rye + 50 g water
• August 1: morning: 50 g rye + 50 g water, tested for bread baking, result: not active enough, feeding continued evening: 50 g rye + 50 g water
• August 2: morning: 50 g rye + 50 g water, evening 50 g rye + 50 g water
• August 3: morning: 50 g rye + 50 g water, evening: no bubbles, discarded all except ~100 g, fed with 50 g rye + 50 g water
• August 4: morning: 50 g rye + 50 g water, evening 50 g rye + 50 g water
• August 5: morning: 50 g rye + 50 g water, evening: big bubbles, the starter is active, CO2 production evidenced by tickling in nose, fed with 60 g rye + 60 g water and 2 x 100 g samples taken for fridge and freezer as fallback points
• August 6: morning: 50 g rye + 50 g water, first successfull bread made with the starter

I show my raw data to illustrate that it’s not straightforward, even with temperature control.

A fool proof starter – is it possible?
What I’m hoping to achieve can be summarized as follows: A “fool proof”, robust and quick method to obtain a sourdough starter that’s as simple as possible, using only flour and water (possibly with addition of some fruit) without having to waste anything of the starter. Temperature is maintained using a thermostated water bath. Preferably it should be possible to adjust the fermentation quotient (ratio of lactic acid/acetic acid) and the total titrable acid content by means of temperature, time and hydration/dough yield.

The products of the Maillard reaction provide tastes, smells and colors that are much desired and lend their charachteristics to a variety of foods. In this post I will focus on the factors that influence how fast the Maillard reaction proceeds. And more specifically I’ll give examples on how the Maillard reaction can be speeded up. This is not about fast food, nor is it about saving time. It’s more about controlling the browning reaction by speeding it up or slowing it down in order to get a desired end result.

The Maillard reaction is, to put it simple, a reaction between an amino acid and a sugar (there’s more on the chemistry at the end of the post). To speed it up you can do one or more of the following:

Chances are you have already utilized this in the kitchen without knowing. When eggs or milk are used for glazing, they act as a protein source for the Maillard reaction, giving a nice brown color. Milk also provides lactose which is a reducing sugar. You’ve probably also observed that temperature does influence browning. Water content is indirectly related to temperature – as long as there is water present, temperature will stay below 100 °C. But once the bread crust dries out the conditions are just right to get the Maillard reaction running.

The same principles are applied to microwaveable pies. The microwaves primarily interact with water and hence only bring the temperature up to the boiling point of water. In order to get sufficient Maillard productcs at these temperatures reducing sugars and amino acids are added to the crust (as exemplified in this patent where dextrose and whey solids are used). Not so surprisingly there is also a patent on how to avoid excessive browning in cookies which calls for addition of a polycarboxylic acid ester to lower pH and hence slow down the Maillard reaction.

Pretzels are an extreme example of how the Maillard reaction can be tweaked. Before baking the pretzels are brushed with lye, a dilute solution of sodium hydroxide, which is very basic. The high pH speeds up the bottleneck of the Maillard reaction (see end of post for details).

A pinch of baking soda can bring out a new taste dimension when browning onions

Another basic ingredient found in most kitchens is baking soda (sodium bicarbonate, NaHCO₃). It’s used as a leavning agent which requires addition of an acid to function. Since it is a weak base, it can be used to increase the pH and hence the speed of the Maillard reaction, for instance when browning onions. This basic task, which isn’t always so easy after all, benefits greatly from a pinch of baking soda (and surprisingly it seems that this hasn’t been done before!). To illustrate this I’ve made a time lapse video of chopped onions being fried with and without baking soda. The frying took 11 min, but things are speeded up about 10x.

Samples taken throughout the experiment are shown in the picture below. Even after 4 min there is a visible difference. After 11 min, the small addition of baking soda has yielded onions which taste remarkably sweet with strong caramel notes, compared to the control which tastes like fried onions.

Another example of how baking soda is used to speed up the Maillard reaction is dulce de leche, a popular sauce/caramel candy in Latin America. It’s made by slowly boiling sweetened milk. Baking soda is not a required ingredient, but is often included. The baking soda gives dulce de leche a darker color and also contributes to the flavor.

Photo by audinou from flickr.com.

It should perhaps be added that baking soda is frequently used in Chinese cooking, for instance in tempura batters and marinades. Once there, the baking soda will certainly speed up the Maillard reaction, but it also affects the texture of meat – I’ll have to return to that topic later.

To round of this post I will briefly touch upon one of the reasons why pH influences the Maillard reaction. The first step involves a reaction between a reducing sugar (depicted as R(C=O)H) and an amino acid (depicted as R’NH2) followed by loss of water to yield a Schiff base. The Schiff base rearranges to the Amadori product (not shown). Of these first steps the formation of the Schiff base is the bottleneck (rate limiting step). The reactivity of the amino acid is influenced by the pH. A simplified reasoning goes like this: At low pH the amino group is protonated, yielding it less nucleophilic. At higher pH, the nitrogen becomes more nucleophilic and at very high pH the amino group can even be deprotonated. It should be noted that the fate of the Amadori product is also in large determined by pH and hence pH will affect more than just the rate, but this is far beyond the scope of this blog post.

We have a small garden with a single tree. It’s a sweet cherry tree and this year must have been one of the best ever. In May it was overthrown with flowers. Last year I made some jam which came out OK, but the drawback with sweet cherries is that their taste doesn’t really compare with that of sour cherries. They’re good to eat, but not as good for cooking and jam as their sour cousins. The summer last year was quite wet and cold which could explain the fad taste, but this year however has been quite hot and the cherries grew darker and sweeter as summer proceeded.

I decided to give cherry jam another try. To improve the flavor even further, I was pondering on adding spices. My mom has previously added cloves and cinnamon to plums when making jam. The first place I looked was under cherries in the book “Culinary artistry”. Among the numerous suggestions for flavor pairings it was black pepper and lemon that caught my attention. Who would have thought? I made a small test batch and was quite pleased by the “bite” provided by pepper so I proceeded with a full batch. I used a pre-mixed gelling sugar from Danisco sugar (which contained sugar, pectin, a preservative and an acid), but you could use whatever pectin you have at hand. Just follow the instructions on the pack (more on the science further down).

Having added pepper and a little of the sugar to get an idea of how it would turn out, it almost felt as if ginger was already there so I added a little more to accentuate that. The other spices were added to round everything off. The pepper taste is quite noticeable if you eat the jam by itself, but on buttered bread or toast it’s really nice. I also suggest that you try it with different semi-soft and hard cheeses such as Emmentaler, Jarlsberg, Prästost, Parmesan or Pecorino. My wife thinks it’s a little to much pepper, but for me it’s just perfect. In German this jam would be known as a Herrenmarmelade (a gentleman’s jam). If you’re not very fond of pepper however it’s a good idea to start with half the amount of pepper.

Spicy cherry jam with pepper
3.7 kg depitted sweet cherries
7.0 g black pepper, ground
0.8 g cloves, ground
0.7 g ginger, ground
1.3 g anis seeds, ground
0.8 g star anis, ground
zest and juice from 1/2 lemon
2.2 kg gelling sugar (with pectin and preservative)

Place enough jars in a cold oven and heat to 120-130 °C to sterilize them (this is more convenient than in boiling water). Depit cherries (conveniently done with a cherry stoner) and cut in four (helps you discover those stones that eluded the cherry stoner). Add spices and bring to boil. Remove any remaining pits that float up to the surface. Pureé with immersion blender (hopefully you will not hear the sound of cherry pits being crushed at this stage). Add gelling sugar. Let boil and skim of foam. Fill the hot jars immediately. And remember – as all chemists know – hot glass looks just like cold glass! Use a canning funnel to avoid spilling jam on the sealing surface of the jars. Leave to cool for 10-15 minutes and then screw on lids. I usually wipe the inside of the lids with 40-60% alcohol and then screw them on tightly before the alcohol has evaporated. There’s more at the end regarding the procedure for closing the jars.

This way of canning is very convenient and the jam will keep for several years in closed jars if kept in a cool, dark and dry place. This is due to the high sugar concentration (sugar binds water, and unless water is available, molds won’t grow), the low pH and – if added – the presence of preservatives. A more tedious way is to sterilize the jars after filling by boiling in water. This is no doubt the best way to sterilize the jars, but for jams with a high sugar content and a low pH it’s a little overkill. The National Center for Home Food Preservation in the US has more information about this (but notice that there are different traditions – I wonder if there is a divide between Europe and North America?). There are also many books about this and good place to start would be the “Ball Blue Book of Preserving”, better known as BBB among home canners. If you chose this method you should probably use a little more pectin as the additional heating at low pH will degrade some of the pectin making the jam more runny.

Using black pepper in a jam worked really well so I googled this and found Clotilde’s recipe for a strawberry jam with pepper and peppermint. She got it from Christine Ferber, author of “Mes confitures: The Jams and Jellies of Christine Ferber” which has recipes organized according to season. As mint was also mentioned as a good flavor pairing for cherries in “Culinary artistry” I thought I’d give pepper and peppermint a try.

Cherry jam with pepper and peppermint
2.2 kg depitted sweet cherries
1.3 kg sugar
2.4 g fresh peppermint leaves
2.8 g black pepper, ground
zest and juice of 1/2 lemon
1 pack of Certo fruit pectin*

Depit cherries and cut in four. Add pepper and peppermint and bring to boil. Remove any remaining pits that float up to the surface. Pureé with immersion blender. Add pectin and stir until dissolved. Add sugar. Let boil and skim off foam. Sterilize and fill jars as in the previous recipe.

[ * The Certo pack weighs 70 g and contains sugar (for easier dispersion of the pectin), citrus pectin, citric acid to get the right pH for gelling and a preservative (ascorbic acid). ]

This jam was dominated by peppermint and the pepper could barely be noticed. I found it very refreshing and there is a surprise element as the red color does not suggest the presence of peppermint. Apart from the obvious use as a bread spread, I can imagine that this jam would be very nice with roasted meat, especially lamb, reindeer, elk and perhaps also wild game.

Having experimented with different spices and peppermint, my wife asked me to also make a batch of plain cherry jam which I happily did. But next year I would like to try making cherry jam with red wine!

As you can imagine, I couldn’t do all this without offering the chemistry behind some thoughts. Pectin chemistry is quite complicated though and there are several types available (low methoxyl, high methoxyl and amidated – so far I’ve only included the two first in “Texture – A hydrocolloid recipe collection”). Commercial packs of pectin for home use do normally not specify which type of pectin they contain, but I assume that it is the high methoxyl which gels in the presence of sugar and at low pH (as opposed to the low methoxyl which requires calcium ions to gel). The easiest is probably to follow the instructions that come with the pack you chose. Always add pectin before you add sugar (unless you premix them). The reason for this is that the gelling of high methoxyl pectins is promoted by sugar. If you add sugar before pectin, it will be very diffult to get the pectin properly dispersed and dissolved (it can be done with an immersion blender though – I’ve tried that once). Ready to use pectin is often pre-mixed with an acid to get the pH below 3.5 which promotes gelling. Citric acid is often used, and plain lemon juice will also do the job. Lowering the pH is especially important when using ripe or over ripe fruit as these can be less acidic and also contain less pectin if we are talking about pectin containing fruit. After the pectin and sugar have been added, the jam shouldn’t boil for more than a couple of minutes as pectin is not very heat stable.

There are also a couple of claims found in jam recipes which I have been wondering about:

Skimming: Almost all recipes I have seen for jams call for rapid skimming of the foam which formes when the jam mixture boils. One explanation I’ve seen is that this is done to prevent growth of mold, as these apparently grow more easily in the foam. There are certainly airborn molds, but the bubbles in the foam come from the jam as it boils, so it’s been very hot and presumably sterilized. So I’m simply wondering if the whole skimming is about esthetics – which is is still a good enough reason to me (but then I wish the recipes could state that!).

Turning jars upside-down: One thing that has puzzled me for a time is why recipes recommend that the jars should be turned upside-down. I’ve googled and checked several books and have come up with a couple of explanations (but most recipes only state that it should or shouldn’t (!) be done, without giving any reason). The fun thing is that the suggested time for how long the jars should remain turned upside-down varies from 2 minutes to several hours when the jam is cool and has set.

• One site claims it is done to prevent larger pieces of fruit from settling to the bottom. This does make sense, and in that case there is no reason to do it if the fruit has been puréed.
• A blogpost commenter suggests that turning the jars upside-down for 5 minutes makes sure the inside of the lid gets sterilized too. The temperature of the jam at this time is probably somewhere around 95 °C, so it does seem reasonable that it might kill some molds residing on the lid. I’d give this a thumbs up. Any microbiologist who could confirm this?
• Personally I have speculated whether turning the jars upside-down would allow water (or jam to be precise) to be drawn into the seal by capillary action and that this helps to make a perfect seal, but several sites emphasize that this should not be done to prevent the seal from being broken (these sites assume that a canner has been used – i.e. sterilizing the filled jars with lids in boiling water for 5 to 10 min). I’m not sure, but I wonder if there is a difference here between screw caps and glass lids with rubber bands?
• A last reason to turn jars upside down would be to prevent the water evaporating from the hot jam to condensate on the lid. If the jars are left to cool upside-down for 10-15 minutes, but turned back before the jam sets this will prevent water to condense on the lid and drip back to the surface of the jam. This water could potentially mean better conditions for growth of molds. This theory is also supported by the suggestion found in old cookbooks where the jars are left to cool completely without lids to let the surface dry and form a skin, and then covered with a filter paper dipped in alcohol before tying them up with pergament paper and string.

The conclusion so far regarding turning the jars upside-down can be summed up as follows. You should chose of the three methods:

• Cover with lid immediately and turn upside-down until cool enough to handle (~40-50 °C). Then return to upright position. This will prevent condensation of water on the lid, it might help create a better seal and it could possibly knock out some molds on the lid. The jam however will most likely not have set yet.
• As above, with the only difference that you leave the jars upside-down until cool and set. This means that the air pocket will not be below the lid but at the bottom of the glass when turned back to the upright position.
• Allow the jam too cool without lids until a skin has formed and the jars are cool enough to handle. This prevents condensation of water on the lid. Wipe the inside of the lids with the highest percentage alcohol available (but do NOT use denatured alcohol!) – typically it would be 40% or 60% – and screw on the lid before the alcohol evaporates. The skin formed will be less suceptible to growth of mold because there is less water present and because of the presence of alcohol.