What Makes Sourdough Sour? It’s All About The Acids


Sourdough bread is characteristic of other bread by the tangy, sour aftertaste which foodies go the extra mile for. But with all bread made from the key ingredients of flour, water, yeast, and salt – how is this achieved?

What makes sourdough sour?

Sourdough is made sour from the acetic and lactic acids which are produced by the bacteria in the sourdough starter. The bacteria eat sugars in the flour and excrete acids. Acetic acid gives the bread a vinegary taste and lactic acid gives a milder yogurt-like taste.

With a simple explanation of the culture at work, now let’s look at what causes different flavors to develop more than others and why some sourdough is sourer.

What Affects The Sourness In Sourdough?

The sourness of sourdough is affected by the conditions in which the starter is maintained, and the fermentation length of the final dough.

The Starter

A starter fed regularly at room temperature, and using a small seed feeding amount, will make less sour bread. Starter stored in the fridge, fed less frequently such as once a week, and using large seed feeding amounts, will produce more sour bread.

The sourdough starter will directly affect the outcome of the bread. The starter is a culture of acid bacteria and yeast, but there are different strains of the microorganisms that can be dominant in a starter culture. The different strains of bacteria will give different sour flavors.

  • Lactic acid is associated with milk products like yogurt and has the milder, creamier taste
  • Acetic acid is found in vinegar – so has a sharper, tangier taste like vinegar

If you have more acetic acid bacteria then it ferments to give acetic acid. More lactic acid bacteria in the culture and fermentation brings lactic acid.

Different conditions can cause different bacteria types to thrive, and this produces a different taste in the bread.

Temperature

Storing the starter under cold temperatures, such as the fridge, will cause acetic acid bacteria to thrive because it prefers this environment.

Storing the starter at room temperature will favor the lactic acid bacteria and create less sour bread. The warmer temperatures require the starter to be fed much more regularly.

Amount of Seed Starter In Feedings

When you feed your starter, most of the starter is discarded to leave a small seed amount for the next cycle. This small amount has enough microbes to multiply when feeding until it has consumed the entirety of the fresh flour.

The amount of seed starter used in feedings will determine how much acid is passed on to the next batch. You are maintaining a level of acidity in the starter by how much you are discarding every time you feed it.

This is typically compared by bakers by using ratios. A 1:1:1 ratio means you take the same weight of starter and mix it with the same water and flour weight. E.g. 50g starter, 50g water, 50g flour. You’ve now got 150g of new starter.

You can bump this up to 1:3:3 or even 1:5:5 which will lower the acidic load transferred from the seed to the new starter – and make less sour bread. This will also affect how fast the starter matures, rises, and is ready for use in a recipe.

Amount Of Starter In The Final Dough

As well as the amount of seed starter used in feedings, the amount of starter which is mixed into the final dough will affect the sourness.

It’s a fairly obvious ratio of more starter, then more sourness. A typical amount would be around 20% starter compared to the flour weight in the recipe (baker’s percentages). But this could be increased to make a more sour loaf.

Frequency Of Feedings

When the culture hasn’t had new food for a while, it starts to starve. This could be around 24 hours if at room temperature, or a week in the fridge as the culture’s activity is slower.

Once it starts to starve, it gets more acidic and will produce a layer of alcoholic “hooch” on the surface.

So to keep a mild-tasting starter, you can feed it more regularly so it never gets to this state. This is typically timed when the starter has risen to its “peak” and is now falling back down. It signals that it has run out of food in its current environment and needs a feed.

Ripeness Stage Of Starter When Used

Once the starter is fed, it will begin rising until it feeds on all the new food. It will rise up in the container until it reaches its highest point – we call this the peak. The peak is seen as the most active point in the starter’s feeding lifecycle.

As a baker, you have the decision of when to use the starter in the dough. We can categorize these periods as before the peak, at the peak, or after the peak.

As you might have guessed, the period after the peak will give the sourest bread because it had the most time to build up the acidity. Using the starter before the peak will give milder loaves and using it right at the peak will give the most rising power.

Fermentation Of The Dough To Boost Sourness

With the starter explained, the second way to control sourness is with the fermentation of the dough itself. This is probably an easier way to control sourness. You can keep the starter preparation consistent and as it’s one small change of fermentation with the final dough.

The key comes down to extending the dough fermentation to allow the acidity to build up. But to prevent the yeast from becoming too active and over fermenting the dough, we must cool it down.

The easiest way to change this is the final proofing stage when the dough is in the proofing basket. For a milder flavored loaf, allow to proof at room temperature for 2-5 hours depending on how active the dough is. For more sour bread, place the proofing basket in the fridge for 8-12 hours. Acetic acid bacteria do their job to increase the tang in the cold.

Should My Sourdough Starter Smell Sour?

Sourdough starter normally smells sour unless it is freshly fed. The sour-smelling acids build up as it ferments, so the sourness can be reduced by discarding and feeding with a small seed amount of the sour starter.

Sourdough starter can smell sour and this is an indication of its ripeness. It gets strong like this with long periods between feedings. A strong vinegary-smelling starter will produce sour-tasting bread which may or may not be to your tastes.

A sourdough starter should ideally be used before it gets to a strong sour smell. By using a milder starter, you can allow the dough to ferment for longer without the sourness becoming overpowering.

It can be rejuvenated to a less strong state by feeding with a small seed amount and by repeating the feeds two or three times before use.

Why Does My Sourdough Bread Not Taste Sour?

Sourdough bread does not taste sour when the fermentation or proofing time was not long enough. Proofing under cold temperatures such as the fridge will encourage fermentation of acetic acid bacteria which produces a sour taste.

You can vary the taste of sourdough considerably by changing a few steps. Bread can be made using a sourdough starter with very little sour vinegary flavors that we sometimes see in strong sourdough.

This is usually when a mild sourdough starter is used and the dough was not cold fermented. By using dough with a large quantity of strongly sour starter, or taking a mild starter and fermenting for long periods at cold temperatures, we get more sourness in the bread.

What Do I Do If My Sourdough Starter Smells Like Vinegar?

A vinegary sourdough starter can be made milder by feeding several times using a small seed amount of the vinegary starter. Using 50g of starter and 250g of both flour and water, and waiting 12 hours between feedings will reduce the acidity.

The goal is to lower the acidity in the starter by diluting it with plenty of fresh flour and water. Using a 1:5:5 ratio of starter to flour and water will achieve this.

Also, giving multiple feeds with short 12 hour rests will ensure that not too much extra acidity is produced in fermenting. But we will still maintain the gluten strength of the starter.

Conclusion

I hope I’ve answered all your questions on what makes sourdough sour. Sourdough can be a bit of a biology lesson, but once you’ve got a simple understanding you can go a long way.

Just remember the fundamentals of the two main acids at work in the dough in lactic and acetic acid. Think of lactic acid as the one associated with milk products and the milder, creamier taste. Acetic acid is combined with water to make vinegar – so has a much tangier taste like vinegar.

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