Cheeseburger in hydrochloric acid

Do ice cubes made with heavy water float or sink?

Exotic ways to cut through butter

Spectacular ways of destroying pumpkins for Halloween

Tea chemistry

See Martyn Poliakoff boil an egg

(Martyn mentions that the yellow color of egg yolks is due to a sulfur containing compound, but I’m not really convinced he’s right about that. The yellow color is mainly due to a group of chemical compounds called xanthophylls which have long conjugated double bond systems that absorb light. And BTW – if you want to dissolve the egg shell in your own kitchen: skip the hydrochloric acid and use vinegar instead.)

Baking a cake in the lab with akward equipment…

… and then figuring out what to do with the cake
(it wasn’t eaten since it was made in a chemical lab)

Mirror images: Carraway and spearmint

Fun chemistry with Crispy creme eggs

Chocolate and roses for Valentines day

As the name suggests, the TGIF posts are a little less serious than what I otherwise post here at Khymos. I hope you enjoy it

I recently stumbled over “Norwegian egg coffee”. At first I thought it was a joke, but it turned out that this is indeed an “egg coffee” – coffee prepared with an egg! I have never heard about it here in Norway, but the fact that it’s popular among Americans of Scandinavian origin in the Midwest suggests that it could be something immigrants brought with them from Norway (feel free to fill me out on the historic origins of this!). I mentioned egg coffee to my mom, and although she had never heard of it before, she did mention that skin or swim bladders from fish were used when boiling coffee to help clearify it. In fact the Norwegian name for this – klareskinn – literally means “clearing skin”. The English name is isinglass (thank’s Rob!). Could it be that the fish skin originally used was replaced by eggs, perhaps due to a limited availability of fish in the Midwest? After all, both are good protein sources.


Egg coffee is amber colored and you can clearly see some precipitate from the egg-coffe mixture. If serving the coffee warm it seems to be difficult to totally avoid the precipitate unless you filter the finished coffee through a cheese cloth or filter paper. The coffee in this picture has not been filtered yet.

When looking into the chemistry behind this it isn’t as strange as it may sound. Fish skin as well as eggs contain proteins. The addition of proteins while preparing the coffee serves two purposes: 1) it helps the coffee grounds to flocculate, allowing them to sink faster to the bottom of the pot (this effect is probably more pronounced when using eggs) and 2) the proteins bind irreversibly to astringent and bitter tasting polyphenols in coffee to form insoluble complexes that will precipitate. The end result is a clearer coffee with a pleasant and mild taste. The bitterness is only barely noticeable, but the coffee still has enough “body” so it doesn’t feel too thin!

Norwegian egg coffee
80 g coarsly ground coffee (rouhgly 200 mL)
1 egg
100 mL cold water
2.5 L boiling water
250 mL cold water

Mix coffee with an egg and 100 mL cold water to a thick paste. Add this mixture to the boiling water, stir carefully and leave to boil for 2-3 min. Remove pot from stove and add the remaining cold water. Let the grounds settle for a couple of minutes, skim off any floating particles, filter through a fine meshed sieve, a cheese cloth or filter paper and serve.

The first time I made this I stirred quite a bit to break up the big lumps. But I was curious whether stirring had any influence on the amount of fine particles, so I repeated the whole process with as little stirring as possible. The lumps of ground coffee where significantly larger, but I couldn’t really see a difference on the prepared coffee. There was however a small difference when looking at the glasses from below (see picture below). My conclusion so far is that there is not a big difference, and that it’s OK to stir a little at the start to break up the biggest lumps. This will also allow a more complete extraction of the ground coffee.

Difference between much (left) and little (right) stirring as the coffee boils as seen from the precipitate at the bottom of a glass of egg coffee.

The addition of the cold water helps formation and settling of the precipitate. Home brewers talk about a “cold break” when they cool wort rapidly in order to precipitate proteins which have been extracted from the malt. And while we’re talking about beer chill haze also comes to my mind. This is the cloudiness that occurs upon cooling beer, and again it’s caused by precipitation of protein-polyphenol complexes. The effect of adding only 10% cold water to the still hot egg coffee is of course limited, and won’t really be enough to give a “cold break”. But since egg coffee has a pleasant taste even when cold, I have decided to cool a whole pot of egg coffee before filtering it. I may post more on how this turns out later, but initial tasting suggests that it’s going to be a very nice iced coffee!

The interesting thing about the protein-polyphenol complexes is that we also encounter them when drinking wine (a quick reminder here that polyphenols is a group of compounds which includes tannins). There’s a nice experiment you can do to illustrate this which has been published on Khymos previously. When we drink red wine, the tannins react with proteins in our saliva to form water insoluble protein-tannin complexes. A precipitate is formed and as a result, the lubricating properties of the saliva are lost and our tongue feels rough and dry. In other words, we experience the astringency of the red wine. To ilustrate this, try the following (I was first introduced to this experiment at the 2004 International workshop of molecular gastronomy in Erice):

Take a sip of a dry red wine, preferably rich in tannin. Keep the wine in your mouth for 10-20 seconds without swallowing. Spit it into an empty glass and watch how a precipitate forms (this might take a minute or two). Notice how the color changes from red to light red or even pink (see picture below). Rinse your mouth by chewing a piece of bread and drink some water. Take a small sip of the wine that you just spat out (if you dare!). Since the tannins of this wine have already reacted with your saliva, it is as if they were removed from the wine, leaving a fad and flat wine without much taste at all.

Top: red wine. Bottom: formation of precipitate in red wine mixed with saliva.

The saliva flow rate and the concentration of proteins varies from person to person (the latter with a factor of 20). Furthermore the flow rate and protein concentration also varies throughout the day and is also influenced by what you are eating/drinking and even by the smell of food. As a consequence, a person with a high saliva flow rate and/or a high concentration of proteins is more likely to approve of a red wine rich in tannins than someone with a low saliva flow and a lower protein concentration. Knowing this, you should not be surprised that wine preferences can be very individual.

In Asia it is not uncommon to eat fruit with salt or even soy sauce. From my own experience, and via friends, I known that fruits such as mango, guava, honey dew melon, watermelon, nashi pears and papaya are eaten with salt. Interestingly salt is used both for ripe and unripe fruit – the latter is especially the case for mango and guava. With unripe fruit I can imagine that the primary motivation is reduction of bitterness. I’ve previously blogged about salt and coffee and how salt in tonic water reduces bitterness – the mechanisms are the same. In addition to the bitterness suppression low concentrations of salt will enhance sweet taste. [1] This would certainly be an advantage in unripe fruit. In ripe fruit there is hardly any bitterness left (or at least I presume that is the case), so here the salt may serve a different funtion. Could it be to balance the sweet taste and give a more savory and complex flavor? Perhaps it could also be explained as increased sensing by contrast amplification?


Nashi pears (Asian pears) are delicious when served in a bowl of salty water!

One particular combination of fruit and salt that I remember from growing up in Taiwan is eating slightly unripe guavas with a beige powder. We would either sprinkle the powder onto the fruit or simply lick it from our hand. The powder had a savory flavor and was a little salty. I can’t remember the name, but from a couple of google searches I’m quite sure that it was a dried plum powder – li hing mui (or just li hing). I see that it’s available from several sellers on Amazon (In fact I just ordered a pack from Hawaii – if it’s the same I used to eat with guavas as a child it will bring back a lot of memories when it arrives!). I found a couple of blogs showing guava with plum powder and masala salt which suggests that there are probably several spice powders used together with guava. The Wikipedia entry on guavas also mentions them being eaten with soy sauce and vinegar (occasionally with sugar and black pepper) on Hawaii, and with a pinch of salt and cayenne powder/masala in Pakistan and India.

Guavas taste even better with a salty/savory dip! For the picture I combined ground star anis with salt and sugar.

As I started to search for combinations of fruit and salt I was overwhelmed by all the different combinations I found. Salt (and other salty food items) are often mixed with other ingredients such as chili or lime. Here’s a small selection of what I found in no particular order:

salt + sugar + chili (Prik-kab-klua)
salt + sugar + chili + lime (Muối ớt)
salt + chili sauce
salt + masala
salt + cayenne
soy sauce
soy sauce + vinegar (+ salt/pepper)
fish sauce
fish sauce + sugar + chili
fish sauce + black pepper
tajin = salt + chili + lime juice
kiam-muy-hoon/kiamuy
li hing mui (dried plum powder)
dried plum powder + sugar
bagoong (salted shrimp paste)
prosciutto
…

One of the few many salt + fruit combinations that has made it to Europe: prosciutto ham with honey dew melon (and some drops of balsamico syrup)

Other more specific fruit/salt/savory combinations I found were:

bananas and guavas with salt and fresh pepper (served in India)
chili salt with fruits such as Granny Smith apples, plums or oranges.
peaches with chili/lime/salt
pomelos with salt and red chillis
Hawiian margarita with Ling Hi Mui powder
…

It seems that eating fruit with salt is far more common in warm countries where an additional intake of salt is recommended due to perspiration. (Update: Lisa comments on her Swedish blog that it could be due to the fact that there are more supertasters in Asia – they are more sensitive to bitterness, hence the additional use of salt) And I admit that my craving for salt does increase when it’s warm. But there is more to this than physiology – the few combinations I have tried are indeed mouth watering – even when tested in cold Norway. And thinking about it, it is really fascinating how plain table salt – one of the simplest (chemically speaking) ingredients we have in the kitchen – has such a repertoire in combination with fruit. There is certainly a lot to try out in the kitchen now – and perhaps some inspiration from Asia for chefs as well?

If you know about or have tasted other fruit + salt combinations, please leave a comment in the section below

Reference:
[1] Keast, R. S. J.; Bresling, P. A. S. “An overview of binary taste-taste interactions” Food Quality and Preference 2002 (14), 111.

One of the good things about living in Oslo are the coffee bars. Norwegians drink a lot of coffe (a healthy dose of 9.9 kg anually per capita, only second to the Finnish) and perhaps that is one reason why there are so many coffee bars around. One of the best (if not the best) is Tim Wendelboe at Grünerløkka. Tim Wendelboe is a previous WBC champion (2004) who now owns a coffee bar and a micro roastery bearing his name. If you visit Oslo and the Grünerløkka area you should definitely walk the additional 200 m from the crowded “Kaffebrenneriet” at Olaf Ryes plass to his shop. And if you live outside Oslo you can buy freshly roasted coffee directly from his website and read more about his coffee adventures in his blog. If you read Norwegian you might also be interested in his recent book “Kaffe”. I’ve enjoyed a lot of coffee from Tim Wendelboe, both in his shop and as beans at home on my Rancilio, and having finished my post “A pinch of salt for your coffee, sir?” I decided to send Tim an email and ask him about his experiences with salt and coffee. I got a very kind reply were he invited me to come and do some tests in his shop. Now that’s an offer I couldn’t refuse!


The coffee roaster is literarily right in the middle of Tim Wendelboe’s coffee shop at Grünerløkka in Oslo.

In his email reply Tim mentioned that he had heard about salt and coffee, but that he’d never done systematic experiments with it. Interestingly, he also mentioned that in Ethiopia it’s common to serve salted popcorn with coffee! What fascinates me the most from all the comments to my last post is how salt-in-coffee is done more or less around the world. It seems as if many know of it, but hardly ever talk about it!

Measuring the small amounts of salt needed is easy with an analytical balance with a 0.0001 g readout, whereas it is impossible on a scale with a 0.1 g readout (which is what you would typically find in a coffee bar). Therefore, as a preparation I had practiced a little at my work, measuring out salt with a standard spatula. When heaped I’d get around 45 mg of salt, when leveled I typically got 15 mg and with the spatula visible all around the salt I managed to repeatedly weigh out about 10 mg of salt. With this I was ready for some experimenting.

A traditional coffee pot (designed by Grete Prytz Kittelsen) was used for the first extraction.

We started off with a coffee from Square Mile Coffee Roasters, a Colonia San Juan. This is a darker roast compared to Tim’s typical roasts, and he suggested this could be a good starting point to test how salt affects bitterness. Measuring out 65 g of a relatively coarse grind, allowing it to steep in 1 L hot water for 5 min + 1 min (after stirring) and dividing the prepared coffee in three, we then added about 45 mg salt to the first 300 mL of coffee. To the second third we doubled the amount of salt and kept the last as a reference. The first observation was that even at 150 mg/L (corresponding to 45 mg/300 mL) the effect of salt is very noticeable. Tim’s immediate response was that the coffee with salt had lost some of it’s structure, appeared less acidic, had somewhat less bitterness, but at the same time was richer and heavier in the mouth. He’s a pro with years of cupping experience whereas I had my very first go with the cupping spoons, so I’ll never get my experiences down on paper like that. They were definitely different, yet both were drinkable. - This could maybe be useful for cold coffee drinks, says Tim. When cold, the bitterness of coffee becomes more noticeable. One way of combating this is by adding sugar. But with a general consumer trend towards less sugar, a tiny pinch of salt could maybe prove useful. Tim said he’d do more tests, and who knows – maybe this year’s summer special will be an ice coffee with a pinch of salt?

We continued with a newly roasted espresso which hadn’t finished it’s degassing yet, giving it some burnt aromas. The effect of salt (10 mg for a double espresso) were more or less like in the previous test. - It’s as if the one with salt is more viscous, says Tim, adding that he values acidity in espressos and that somehow the salt removes some of this acidity. From the litterature on binary taste interactions it is known that low/medium salt concentrations will enhance sourness whereas higher salt concentrations will suppress sourness. Based on this it sure seems as if we hit the “high” level with respect to sourness (but the experiments we did were of course in no way scientific). I tried one espresso with roughly 2-3 times the amout of salt (20-30 mg for a double espresso). When first tasting it carefully in the front of my mouth I felt it was almost sweet whereas Tim spit it out immediately. I then tasted it again towards the back of my tongue and this time I felt the salty taste too. Quite fascinating how the tasting technique gives different results. These tests also demonstrate how bitterness is linked to and influenced by sourness.

To end it all we tried adding salt to espresso with steamed milk. It turned out that a dose of 10 mg for a double espresso was difficult to discern from the reference. We added more salt and were surprised how much salt could actually be added before it became noticeably salty. But it remains to be seen if salt will make any difference in the end when adding milk. With all it’s proteins, milk is so powerfull in altering the coffee flavor and damping bitterness that a little salt simply won’t make such a big difference.

Apart from the potential use in cold coffee the I guess one conclusion is that high quality coffee from a micro roastery is good by itself. There is no need for salt, but salt can be used to knock out some acidity (as well as some bitterness), resulting in a coffee which is more compact, not so fresh, but with a fuller taste, mellow … and simply different. But as always – more experiments are required. I also think that the effects of salt were best demonstrated with plain hot water extraction. Espressos are so overwhelming and strong that the taste buds quickly tire from tasting a couple in a row. Lastly, I’d also be willing to hypothesize that salt can do more for average (or even poor) coffe beans and/or poor extraction technique than with first class beans prepared in the best possible way. And if you’re in doubt wheter there is a large difference between the quality of coffee beans, take a look at the picture below.

Coffee beans are pale green before they are roasted. The difference between good beans (top left) and bad beans is significant, as Tim showed me. If you think the bad beans are discarded – think again. They’re sorted out one by one and end up in your super bargain coffee!

Again I was lukcy that all the practical details worked out so I could attend this year’s Flemish Primitives in Brugge. For some one who’s not attended, it’s not so easy to grasp the concept and ideas behind The Flemish Primitives (TFP). And I admit, even though I’ve been there twice it’s not so easy to convey it in a short way. First of all the name is rather cryptic (unless you’re into art) as it refers to early Netherlandish painting. The link to food is described as follows by the organizers of the event (my highlights):

In the 15th and 16th century, ’The Flemish Primitives’ were masters in combining their talent with new techniques. Techniques they developed by interacting with other disciplines like manuscripting, sculpting, etc. This way of working changed the painting techniques in all of Western Europe forever. The event ‘The Flemish Primitives’ wants to continue in the same spirit. Respect for food products and beverages, the knowledge of the classic cooking techniques combined with a stimulation of new techniques and creativity. By promoting interaction between scientists, the world’s most famous chefs and artists, the event wants to deliver a creative boost for the food industry and gastronomy in Belgium and the world.

Considering last year’s sucess it was no big surprise that this year’s event was sold out (and the foyer of the Concertgebouw was equally full in the coffee breaks). And with the memories from last year I arrived in Brugge with great expectations. One main difference from previous years was that the scientific parts were much better integrated throughout the day. Scientists were on stage alongside the chefs, explaining their work. Also, contrary to last year’s back stage kitchen, they had now moved the kitchen onto the stage, flanked by a bar, some sofas and laboratory mezzanine. A good decision!

Flavor pairing (or food pairing as they call it) was the main topic of last year, but even this year flavor pairing was mentioned throughout the day by several people. It’s also obvious that Bernard Lahousse and his team have worked hard to get some of the sponsors of the event to incorporate the idea into their printed material (Belcolade and SOSA).

Flavor pairing diagrams like this one were incorporated into the Belcolade (= Belgian chocolate company) handouts. Similar diagrams for a great number of food items can be found at the food pairing website.

As I see it, one of the main objects of TFP is to find (or even create) new sources of creativity for chefs. And art, science and cooking can indeed be a fruitfull mix for creative exchange and development. Working as a chef is all about constantly finding new sources of creativity. Even among the very best, one can find signs of creative fatigue – it suffices to mention Ferran Adria who recently announced that el Bulli would close down for two years (2012 and 2013). He gives several reasons, but The Times Online reports that according to Spanish culinary insiders the “effort needed to keep dreaming up mouthwatering wonders, has worn him down” (more in a recent Q&A from WSJ). Ferran does however promise to be back in 2014!

TFP 2010 included presentations of five novel technologies and concepts. These included the use of very high pressure for processing of seafood and fruit. This is commonly done in the food industry for preservation purposes, but now it was used mainly for the textural and flavor changes induced. A second device shown was a combined vacuum and freezing chamber were the freezing was effected by liquid nitrogen, allowing virtually any temperature between 0 and -150 °C to be reached within minutes. Regrettably I missed part of the presentation of the third device (due to break out sessions that were running alongside the main program – more on those later). But from the pictures it seemed to be a microfluidic device for precise delivery of flavor essences (feel free to fill me out on this one in the comments!). The last machine presented was a kitchen emulsifier for preparation of emulsions as viscous as Nutella. I’ll post pictures and more info on the gadgets in a separate post.

In the preparations to this years event surveys with chefs and consumers had led to the forumlation of 10 statements on the identity of Belgian gastronomy, which in essence are not too different from the Statement on the ‘new cookery’ which was formulated by Ferran Adria, Heston Blumenthal, Thomas Keller and Harold McGee back in 2006. I think they are well formulated and it’s hard to disagree with any of the statements. I also belive that most of them could be adopted by many chefs world wide by substituting their own country into the statements. I bring the statements here in extenso for your convenience:

1. Local ingredients. Work with regional products.
2. High-quality ingredients. Work with products of the best quality available preferably in Belgium. Work with seasonal products in the right season.
3. Producer orientation. Chefs have the power to control the quality of the ingredients by making specific choices and demands. Belgian chefs are partly responsible for the motivation of producers to supply the highest quality.
4. Consumer orientation. Chefs have the power to broaden the palate and to revalue or upgrade specific products by paying attention to forgotten, seasonal and local products, or products with low intrinsic value.
5. Inventiveness and openness. Be open to new techniques and products. Strive for innovation and improvement.
6. Inventiveness and cooperation. Strive for intensive cooperation between chefs, the industry and the scientific community. Information exchange is particularily important, also between chefs.
7. Innovation and tradition. Innovation and tradition are not opposites. Have respect for traditional Belgian cuisine by including this respect or tradition as such in dishes.
8. Tastiness and well-being. Strive for food which is tasty above all, but also keep in mind to provide a state of well-being during and after the meal.
9. Moral responsibility. Strive for the use of products that have been produced in an ethical, ecological and sustainable manner.
10. Multisensorial tastiness. Strive for an optimum and ample stimulation of all senses of the consumer. Create a socially agreeable and exclusive experience.

Apart from all the journalists present this year there were also a couple of food bloggers present. You may already know the blogs which mainly focus on restaurant reviews: Very good food (Denmark), Food snob blog (UK), High end food (Germany), Food intelligence (France), Cuisiner en ligne (France) and Gastros on tour. I had a chat with some of them and they all have non-food day time jobs, just like myself. Like last year I plan to write several posts on various topics from TFP – and I will publish this as soon as time allows. But in the mean time, check out the blogs mentioned for a perspective and covering of TFP 2010 that will probably be different from mine

Update: There were more food bloggers present: Coolinary (Belgium), Der Kompottsurfer (Germany).

-
I also visited The Flemish Primitives in 2009. You can read more about that in my four posts from last year: The Flemish Primitives: A travel report (part 1), Chocolate surprise (part 2), Heston Blumenthal (part 3) and Glowing lollipops (part 4). Final note to readers: This year my travel expenses were covered by TFP and the tourism bureau of Brugge.

If Richard Wiseman’s fork balancing trick is not challenging enough, why not try the fork balancing trick I did for part 8 (where I encourage experimentation in the kitchen) of my Ten tips for practical molecular gastronomy series. You only need two forks, two skewers, a wine cork and a little patience. If interested you can read more about the physics behind the balancing fork trick.

As the name suggests, the TGIF posts are a little less serious than what I otherwise post here at Khymos. I hope you enjoy it

Miss Silvia is full of surprises! She’s been around the house for a year, but only now did she reveal one of her hidden capabilities. Did you know that you can make scrambled eggs with the steam wand of your espresso machine? Me neither. It’s a brilliant idea and one can wonder why no one has done this before. I mean, espresso machines have been around for a while. And as it turns out – according to Kelly’s comment below this was done in San Francisco back in the 90′s. It seems as if the credits for rediscovering these scrambled eggs should go to Chef Jody Williams (and thanks to Jessica at FoodMayhem for posting this). I’ve tried it several times and it works very well. I’d even say that this gives you another reason to purchase an espresso machine with a proper steam wand! Many other reasons can be found in my first post about Miss Silvia.

This is how I make the scrambled eggs: I crack 3 eggs in a 600 mL pitcher (normally used for steaming milk) and press the steam button on my Rancilio. After approx. 10 seconds I empthy the wand of water and wait for another 30 seconds to allow pressure to build up before I start steaming the eggs. Notice that I didn’t even whisk the eggs with a fork – the whirling effect of the steam wand is strong enough to get the eggs properly mixed. With my Miss Silvia it takes about 50 seconds before the steam breaks through to the surface. The eggs actually set in the pitcher and I used a spoon to scoop the eggs out and put them on a plate. Scroll to the end of the post for a video illustrating the whole process.

Make sure you clean the steam wand very well after using it for eggs. The best way of softening the protein residues is to immerse the steam wand in cold water.

I have tried to add a little milk to 3 eggs before steaming, but interestingly I wasn’t able to get this mixture to set properly. I say interestingly, because even though the scrambled eggs failed I figured that steaming perhaps could be a good way of preparing custards. Holding the pitcher one has pretty good control of the temperature, and also very efficient aeration. It could even that this is a more robust way of preparing a custard? This needs experimenting – and you are more than welcome to join me! And why stop with custard? How about a sabayon? Basically any egg based sauce could be prepared with a steam wand.

Update (added on October 25th)
In the comments there was a question about what would happen with egg whites. I had 3 leftover eggwhites so I added some sugar and tried to steam them. They fluffed up very fast and I was not able to control the process. I spooned the result onto a plate and as you can see the result was quite regrettable. The whites lost a lot of liquid.

I also tried to make a simple sabayon using 1 egg yolk, 30 g sugar and 60 mL of white wine. I got a frothy texture, but when I poured into a glass it separated quite fast. I think the main problem here is scale – on such a small scale it’s really difficult to control the temperature. I presume that this could be easier to control by tripling the amounts.

[Found via the Norwegian food blog Ordentligmat]

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.

Inspired by the Swedish bread blog Pain de Martin which I recently discovered I decided it was time to have a go at sourdough breads! Although one of my favorite types of bread it’s a long time since I gave it a try and even longer since I actually succeeded. Leaving apple peel covered with water for two weeks in a cool place (15 °C) I got a light apple cider which I used to make a starter some years ago. I followed a recipe from the Norwegian artisan bakery Åpent bakeri and it gave a marvelous bread. But since then I’ve tried to repeat this twice without success. No wonder that even Rose Levy Beranbaum in her book “The Bread Bible” writes that she didn’t intend to include a chapter on sourdough at all. There’s no doubt that sourdoughs are tricky, but I was a litte surprised and disappointed that someone who sets of to write a 600+ page book on bread even considered to skip sourdough… Luckily she changed her mind and the introduction has a fascinating nice-to-know fact: 1 g flour contains about 320 lactic acid bacteria and 13000 yeast cells!

I believe one the reasons why sourdoughs seem to live their own lifes sometimes is that they need to be kept in a warm place. My kitchen isn’t that warm so I figured it was time to use my immersion circulator and give sourdough another chance (who says you can only use immersion circulators for sous vide anyway? – I think my next project will be to make yoghurt!). With a thermostated water bath keeping a sourdough starter at constant temperature is as easy as 1-2-3. But surprisingly I haven’t seen any blogposts yet from people using their sous vide water baths for sourdough starters (although some have built their own water baths for this purpose using aquarium equipment).


Fresh apple peel in water. This particular experiment failed – the cider smelled OK, but there was quite a lot of mould on the surface after two weeks so I didn’t dare to proceed …

It was Martin’s post on an apricot starter that triggered my desire for sourdough (but careful – never close your jar with a rubber as shown in his picture!). I got a bag of dried apricots and gave it a try. There was some bubbling and it smelled quite nice, but the bread dough never rose properly. I later found out that in a comment to the first post and a later post on the same topic it was pointed out that the apricots should not be treated with sulfur dioxide or a sulfite (used to conserve the fruit, appears on labels as E220-228 in Europe). That’s very obvious once you think about it, because the sulfur dioxide/sulfite is there to kill microogranisms and increase shelf life. For a sourdough however you want living microorganisms! The solution to this is to use untreated dried apricots. I haven’t been able to find any yet, but I’ll definitely give it a new try once I find some! Other options of course are to use dried or fresh apples, pears, grapes – preferably not treated with pesticides or sulfur dioxide – as the surface of these fruits are host to many yeasts.

A relatively firm rye starter with 150 g water and 200 g whole grain rye flour (left) shows signs of yeast activity after 24h at 28 °C (right).

Having failed with the apricot starter I decided to give a traditional rye sourdough a try, using a recipe from the book “Brød” (=bread) by “Åpent bakeri”. I got a nice bubbling after 1 day, but the starter was pretty dry. As I discarded a portion and fed more flour and water to the starter it seemd as if it died… I (believe) I followed the recipe very accurately (except for the very first day where I opted for a hydration of 75% instead of 60%), but the final dough never rose, so I had to cheat and add bakers yeast in order to actually get the breads baked. Acid production was fine however and the resulting flavor was very delicious and I got the crumb that I desired! However, with all these problems I figured it was time to turn to the scientific litterature and read more on sourdouhs … More on what I found out in a follow up post.

One last thing: Despite my limited experience with sourdoughs I’ve already been a little annoyed by recipes for starters that require one to discard a significant portion of the sourdough every day before feeding the start with more water and flour. One obvious way around would be to start at a much smaller scale so that every feeding can be done without having to waste any sourdough. In fact Kurt Janz already has a post with detailed instructions on a less wasteful sourdough (and he BTW has one of the most comprehensive sites on sourdough I’m aware of including a sourdough calculator). The only reason I could think of why one perhaps would want to use more than a couple grams of flour to start with would be to outnumber any unwanted yeasts or bacteria from the air or the equipment. Is this the case? Are there any other reasons? To circumvent this one would simple have to work very clean and wash all equipment properly.

Just a small reminder that the deadline for the current round of TGRWT #17 is a little later than usual: May 8th. I took the picture above for last month’s TGRWT (where it was combined with chicken) and came to think that it actually qualifies for this month’s TGRWT as well. It’s rose foam on a spoon with apple, celery and almonds, and the foam is sprinkled with a little pepper.

As an experiment I tried to freeze the leftover rose foam and was quite surprised by the resulting texture. It was easy to scoop due to the incorporated air and had a nice mouth feel. There were no ice crystals and the texture was almost a little chewy. What would one call this? Ice cream? Sorbet? No – there is no cream and the texture is much lighter. Frozen sorbet? Foamed sorbet? Frozen foam? Any suggestions? I think I’ll make a variation of the frozen foam for TGRWT #17

Frozen rose foam

Frozen rose foam is easily scooped due to all the air bubbles