What is Yeast? Yeast is all around us, in different forms. It’s a single cell organism without which life would be all the poorer. We know that bakers use it to make a dough ‘rise’. Without it, our bread would be like flat, hard cakes. A little understanding of how yeast works and what it needs will improve our baking. And reduce our failures.
In the days when people made their own bread, they would go to a brewer and get a jug of fluid and yellow brewer’s yeast.
Nowadays, yeast is made commercially on a large scale. The yeast you buy at the shops is compressed into moist blocks of a grey / yellow plasticine like mass. Fresh yeast like this is my favourite form of yeast. It produces a better flavour in the bread and is easy to use, but its shelf life can be a problem if you don’t bake frequently.
Also, if you don’t live in or near a city you may have problems buying fresh yeast. For that reason, all the recipes in the blog use yeast in a dried form.
Yeast types.
As far as our bread is concern, we have four options we can use: –
Fresh, or ‘wet’ yeast.
As I’ve said great to use, but a problem to find and store. If your local wholefood store doesn’t sell a lot of yeast, it may be deteriorating before your get your hands on it. Also, as the wastage can be high, so shops will charge a premium for fresh yeast. fresh yeast can be crumbled directly into the flour or used to make a ferment (my preference).
Freezing fresh yeast.
You can freeze fresh yeast. Wrap it in tinfoil and if you have it pop the parcel into a small bubble wrap bag then freeze. The bubble wrap will protect the yeast from the harshness of the freezer and prolong its life.
The yeast will be fluid when defrosted and you will need to add a little more to the recipe when making the dough. This is because some of the yeast cells may have been damaged during the freezing.
Natural yeasts – sourdough.
This is a simple basic process where we mix flour and water together and allowing the natural airborne yeasts begin to ferment the batter. This is then cleaned and fed each day for five to seven days to make our ferment, or sourdough starter as it is known. Look up our post on making your own sourdough starter.
The long slow proving needed for sourdough produces a bread with great flavour and keeping qualities. Nothing beats sourdough toast!
Dried yeast.
This is fresh yeast dried and compressed into pellets. Usually sold in a small tin and needs to be mixed with water before use. DO NOT add it directly into the flour as it will not dissolve in the dough. Works fine, I would always recommend making a ferment to make sure the yeast is properly dissolved.
Fast Action Yeast.
This in the one you buy in the little tin foil pouches. Originally developed for bread making machines this is a finer grain. This means it will dissolve in a dough without pre-mixing with water. The ‘Fast Action part is because vitamin C has been added to the yeast to supercharge it and help the machine produce a lighter loaf.
Changing from fresh to dried yeast.
Both are fine to use at home and there is a basic rule for converting a recipe from fresh yeast to dried or visa vera. Use half the weight of dried yeast to the fresh quantity. And of course, use double the weight of fresh yeast to dried in the recipe.
How yeast works.
Yeast requires sugar (glucose) before it can ferment. Luckily, yeast contains enzymes which are capable of changing both cane sugar, (sucrose) and malt sugar (Maltose) into Dextrose. So almost any sweet material (except milk sugar) will assist in fermentation.
The problems with sugar
As wheat flour already contains 2.5% of these sugars. Any mixture of flour and water will readily ferment without the addition of any extra sugar. What’s important is the concentration of sugar that the yeast has to cope with. A dough with more than 12% sugar will be inhibiting the actions of the yeast. This must be remembered when doughs are made which are very rich in sugar. The yeast content must be increased to compensate for this effect. I would always use a ferment as well to give the best chance of success.
High fat breads.
Excess, fat, salt, sugar, and spices all slow down the progress of the yeast. Where we have a dough with very high concentrations of fat like a brioche dough. The majority of the fat is added to the dough at the ‘knocking back stage’. This give the dough time to prove and develop before the fat is worked in.
Salt.
Direct contact with salt will kill yeast. 7-10g of salt per 0.50kg of flour should be plenty for the dough without inhibiting the action of the yeast too much.
Making a ferment.
This is something a like to do. And is beneficial for the dough, particularly rich doughs like my walnut bread.
Take the yeast and mix to a smooth paste in a small dish using blood temperature water. The mix should be the consistency of double cream. Add a good pinch of the flour you will be using and mix in. over the dish with a tea towel and leave to stand for a while. When the yeast is bubbling and has risen in the dish your ferment is ready to use.
And that’s where the term ‘Proving’ comes from. Many years ago, before modern cold storage you couldn’t be sure if the yeast was still active enough to make bread. Mixing the yeast with flour and water and seeing it ferment and grow proved the yeast was fit for use. Today we still do this but for a different reason. It allows the yeast to get a head start. And begin to multiply before having to cope with concentrations of fat or sugar.
Temperature.
How many times have you seen ‘warm’ water specified in a bread recipe or prove in a warm place? The problem here is our interpretation of ‘warm’. You may have noticed above I specified ‘blood temperature water’ for making the ferment. We are warm blooded, so anything warm feels neutral to us.
Yeast is dormant at (0°c) but as the temperature increases so too does the activity of the yeast until at (49°c) it becomes killed. The best working temperatures are between (21-28˚c).
Without understanding this, it is easy to be tempted to ferment yeast at too high a temperature. Even 28°c) feels comparatively cool to the touch. Too high a temperature causes the dough skin ove and spoils the formation of the interior of the bread.
If you’re not sure how warm your water should be, here’s a simple baker’s trick.
Take the temperature you want your dough to be, let’s say 26˚c then double it, that’s 52˚c.
Take the temperature of the flour you are using. Let’s say it’s been in the larder and is only 18˚c.
Take that from the target temperature, and that’s the water temperature you need- 52˚c-18˚c =34˚c.
So, when you are making your bread remember it’s a living thing. Using yeast is not unlike growing a plant. You start with a few cells that need to cared for in the right way.
Not too hot, some moisture, be careful with the minerals and your yeast will grow and flourish. And of course, so will your bread.
Enjoy life!
John.
©John Webber. 2023