What is a sponge?
Let's make a sponge. What does that even mean? And what does it involve?
A sponge is basically a very wet dough that is allowed to ferment very slowly for a very long time. To make it ferment, it needs some yeast, but to ferment for a very long time it needs to be a very slow acting yeast.
Commercial yeast is factory produced (even the fresh variety) and is specifically designed to act very vigorously, so that it can raise dough very quickly. It's all about producing gas. This is absolutely not what sourdough is all about: it's about producing flavour and texture.
The yeast that a sourdough sponge uses is natural wild yeast, designed by nature to act slowly by breaking down the complex "stuff" in good flour into less complex "stuff" plus various good gut-friendly acids, and a bit of gas. You can see I am not very scientific about this. I don't feel it is important to understand the details, but it is very important to recognise the good effects that result from this process.
Why is sponging a good thing?
The good effects that a long slow fermentation produces are -
- really good flavour
- much more strength and sponginess in the body of the bread
- generally open texture
- crunchy crusts on day 1
- more digestible bread and a happier gut
How to describe a recipe
If you are making a batch of dough for a couple of loaves, the recipe might call for 700 g of water and 1 kg of flour. The ratio of water to flour in the final dough is 700 : 1000 so the hydration level is 70% - quite a soft dough. You can work this out very simply on a calculator. Just divide the weight of water by the weight of flour, and multiply the result by 100 to get the hydration percentage.
The recipe uses 1700 g for 2 loaves, but after it's been in the oven, the bread will probably only weigh 1600 g. So you could describe the recipe as "2 800 g loaves at 70% hydration".
How to describe a sponge
The sponge is typically made up with half the total water that the recipe calls for, and a quarter of the total flour. It is often called a quarter sponge. You include some sourdough starter culture in the sponge, but you don't add any salt at all.
The sponge for the recipe above would be made up with half the water (350 g of water) and a quarter of the flour (250 g of flour). The ratio of water to flour is 350 : 250 so the hydration level can be worked out like this -
The sponge's hydration level is 140% - twice as wet as the recipe calls for in the final bread. Keeping the starter culture at 140% hydration means it is at the same hydration level as the sponge. This is well worth doing, in my experience, because it simplifies matters a lot.
Making a sponge at 140% hydration gives the wild yeast ideal conditions -
- plenty of fresh food in the form of wholemeal flour (organic so it is pesticide free)
- plenty of water
- no salt
- reasonably warm conditions (at least compared to the fridge!)
Making a dough using a quarter sponge simply involves adding the other half of the water, the other 3 quarters of the flour, and the salt.
Yeast for use in a sponge
So where do we get this wild yeast? The answer is of course that it's everywhere - in the air, on the grain (especially rye), and on the skins of fruits, provided the farmer hasn't dosed it with pesticides.
If you have ever cycled through a vineyard at harvest time, when the grapes are practically drunk with their own juice starting to ferment in their skins, you will know what I am talking about.
|San Francisco sourdough culture under the microscope|
So all you really need to be a sourdough baker is a bottle or plastic jar in the fridge to keep your yeast genie in. You can spend as much or as little as you like on equipment, but you can't economise on time or commitment, or it just won't work.
Getting started with a sourdough culture
Because the grains that flour is made from are covered in wild yeast, wholemeal flour by definition also contains wild yeast. So to make a new sourdough culture from scratch, you need some wholemeal flour (organic so you know there is no pesticide in the flour) and water. Nothing else.
Just out of interest, I thought I'd prepare a rye culture ahead of Sourdough Saturday at the Heron Corn Mill. Here are my pictures showing what it looked like at various stages of its development.
Day 1 Monday 31st October 2016
First zero the scale with an empty glass jar, so we are weighing just the ingredients. I do this each day as the first step so I am always recording just the weight of the ingredients, and not the jar, each day. [Make sure you can recognise the jar next time you need to use it to zero the scales: empty glass jars tend to look similar!]
Next add my standard feeding quantity - 50 g of flour - to the jar.
Next add 70 g of water, making 120 g of starter.
Calculating and recalculating the hydration percentage
The important thing to realise about sourdough is that you need to know what has gone into it. And this is at least as important when you are making a starter and a sponge. It's not the total amount that's important, it's the amount of water, the amount of flour and most of all the ratio of water to flour, in terms of weight.
My starter has 70 g of water and 50 g of flour. The ratio of water to flour is 70 : 50. Use the calculator to check what that is as a hydration percentage. 70 divided by 50 multiplied by 100. The hydration level is 140%.
So I added another 70 g of water to loosen the mix.
[Note: I unwittingly made a rod for my own back here. From this point onwards I need to be extra careful to keep track of how much water and how much flour I put in, so I can be sure what the ratio of water to flour is. You can avoid this complication if you like by deciding once and for all that every time you add so much flour you will add so much water, and sticking to it. By day 5 I am beginning to wish I had! Still, it's all good practice at working out the hydration level.]
I've now got 140 g of water and 50 g of flour, so the ratio of water to flour in the starter at this stage is 140 : 50 which is 280% hydration. It doesn't matter what the actual figure is at this stage, because it can be adjusted later. The key thing is to get a nice wet mix so the yeast can get to work in ideal conditions. And you need to write down exactly what has gone in - you won't remember.
I then loosely put the top on the jar and left it in the kitchen overnight to get started.
Day 2 Tuesday
Next day I inspected the starter, but there wasn't much going on yet.
And another 70 g of water.
So now I have 210 g of water and 100 g of flour. The ratio of water to flour is 210 : 100, which is 210% hydration.
I left the starter in the kitchen again with the top loosely on overnight. Next morning there were still just a few bubbles.
Day 3 Wednesday
At this stage I thought maybe it was time to give the starter a bit of a kick, so I transferred it to the warmest place in the house - over the poorly insulated hot water tank in the airing cupboard. In the evening I fed it with another 50 g of flour and 140 g of water, to keep the mix nice and wet.
So now I have 350 g water and 150 g of flour. The ratio of water to flour is 350 : 150 and so my hydration level is 233%. Hopefully something will happen soon.
At last! Some action!
By the end of day 3 I am starting to see some bubbles. The smell is still quite sweet and pleasant, so I'm happy to let it keep doing what it is doing and not interfere while it is going well.
Day 4 Thursday
By lunchtime on day 4 my weekly bake is complete. My magnificent wholemeal recipe has delivered again, in spades, and my sourdough has survived sticking to the peel.
More to the point, my starter is clearly on the road. It smells nice and fruity at the moment, though I don't expect that to last. The bubbles are forming a fairly distinct layer of thick froth at the top of the jar, so I am going to start giving it a stir now and then.
By teatime today the starter has developed a thick almost crusty top layer, and a fine malty smell. The taste is not so nice - a mixture between stewed plums and something medicinal. It seems like war has finally broken out in the jar, and I think it is now time to start cutting the mix back. This simply means that before my next few feeds I will throw half the mixture away. It sounds wasteful, but over time one strain of yeast will become stronger, and will overpower the others. Cutting back and feeding will encourage the strongest strain to keep growing more and more dominant. It's just accelerating the process of natural selection, really. It also means I don't need a bucket to hold the culture - a jar is big enough.
Once one strain of yeast takes control of my culture, it will start to become less volatile, and it will be worth risking using it to bake with. And it is a risk, believe me!
By the end of the evening the starter has developed quite a pungent bouquet, and is decidedly sharp to the taste.
Time to act!
The first thing to do is check that the jar contains what I think it contains. Reading back through my notes from last night, I think I have 350 g of water and 150 g of flour, at a hydration level of 233%.
OK, the starter now weighs in at 496 g so I have lost 4 g to evaporation, but basically I am right. Now let's harden our hearts and throw 50% away.
That's dealt with my evaporation, anyway! Now I haven't changed the ratio of water to flour - I've just thrown some away. I now have 175 g of water and 75 g of flour. My starter is still at 233% hydration. It is important to do these calculations again, so that I know what I have got in my jar at all times. Remember, you need to keep a track of 3 things -
- the amount of water
- the amount of flour
- the ratio of water to flour
And throwing away half the culture only involved wasting 75 g of flour, which at £3 for 1.5 kg is 15p - hardly breaking the piggy bank. Now I can feed the starter with my usual 50 g of fresh flour.
And another 70 g of water.
By the way, if your water is chorinated, Vanessa Kimble (Bakery Bits sourdough correspondent) suggests leaving it to stand for a few hours before using it in your starter. I've never thought chlorine was a problem with our lovely lake district water, but it's worth thinking about anyway.
Finally, recalculate what is in the jar. I had 175 g of water and added 70 g so I have 245 g of water. I had 75 g of flour and added 50 g so I have 125 g of flour. So the ratio of water to flour is 245 : 125. Work out the hydration percentage on the calulator by dividing the weight of the water by the weight of the flour and multiplying the result by 100 -
So I am taking forward to day 5 a starter with 245 g of water and 125 g of flour, at a hydration level of 196%.
Day 5 Friday
This evening my starter has a robust crusty looking top layer and a fairly pleasant smell somewhere between beer and pear drops. The pear drops however suggest that things could still turn nasty, so I am keeping a close watch.
The first surprise is that the jar which yesterday weighed in at 370 g, today weighs in at 380 g. I have no idea what has happened there! Something to puzzle over with a bit of unpasteurised camembert "avec son verre de vin rouge" and some of yesterday's wonderful bread.
One jar weighs 14 g more than the other. So the apparent increase in the weight of my starter was caused by zeroing the scales with a lighter jar. Simples. Far from increasing by 10 g, the weight had in fact gone down by another 4 g due to evaporation. So in the following pictures, I need to reduce the weight shown by 14 g.
I now have 176 g of starter (14 g less than shown on the scales) at 196% hydration. That is 117 g of water and 59 g of flour. Now add 50 g of flour.
And 70 g of water.
The sponge is getting close to my preferred final hydration level of 140%, but it is also getting a bit thicker than I would like, so if I don't like the look of it tomorrow, I will add some more water to slacken it again. I can always adjust it on the momentous day I finally bake with it.
The first sponge - entering maintenance mode
I think you have got the idea now of how to make a starter from scratch. There are only so many photos of a jar of flour and water that you can stand.
Assuming you have persisted with the cutting back and feeding until the culture has become less volatile, you will eventually feel it is time to let the beast loose, and see what happens when you bake with it.
This is a big day for your starter, because it marks the point where it begins the rest of its life. From now on it will generally live a life of seclusion, in the fridge, contemplating what might have been.
And occasionally, life will brighten up, food will be plentiful for a while, and then just as suddenly, it will find itself back in the fridge, feeling refreshed, but ready once more for an indefinite sleep.
You will have to learn a new routine as well. Two days before you want to bake, you need to get the starter out of the fridge and feed it, keeping the ratio of water to flour the same. So if your starter in the fridge consisted of 70 g of water and 50 g of flour, or 120 g of starter at 140% hydration, feed it another 70 g of water and 50 g of flour, making 140 g of water and 100 g of flour, or 240 g of starter at 140% hydration.
And in the evening top it up so that you have the right amount for a quarter sponge plus the original 120 g of starter you took out of the fridge. That means you can take a fresh 120 g back and put it in a clean jar in the fridge to be your refreshed starter for next time you want to bake.
If your recipe asks for 700 g of water and 1 kg of flour, your quarter sponge would consist of 350 g of water and 250 g of flour. So you need to top up your mixing bowl so it contains 420 g of water (350 g for the sponge and 70 g for next time's starter) and 300 g of flour (250 g for the sponge and 50 g for next time's starter). The ratio of water to flour in your mixing bowl will be 420 : 300 or 140% hydration. So not only will your sponge be at 140% hydration (twice the hydration for the finished bread) but the 120 g you take back for next time's starter will also be at 140% hydration.
Your brain will be hurting
Too much arithmetic already! But it really is worth thinking through all the steps and checking your figures at every stage. Eventually it will become second nature, so long as you stick with it.
Fortunately, it's not just you that needs a bit of quiet time after all that arithmetic. The sponge needs to be left alone overnight, with just a tea towel over the mixing bowl, so it can get on with the really slow job of breaking down all that new food you just gave it, and making a lovely wet, gloopy, tangy, sour dough for you to use next day in your baking.
You can go to bed secure in the knowledge that your starter is back in the fridge, refreshed and ready for next time. And your sponge will be ready to go when you are ready to make your lovely sourdough bread next day.
Just one thing, and this is very very important: don't forget to take back the 120 g starter and put it in the fridge. I have done this on a number of occasions, and my best advice is to have a written routine, and include a written reminder to check you have done it. You WILL curse when you forget!
Making sourdough bread using a quarter sourdough sponge
Wel,, that's another story...