Different forms of yeast

Posted on 03. Jan, 2013 by virtuousbread in Bread and conversation

What is the difference between instant yeast and dry yeast?  How can I substitute for fresh yeast when I cannot get any?  How do I use a sourdough starter in a recipe that calls for yeast?  Recently I have had a lot of questions about yeast so it was about time to write a little post to answer the FAQs.

Yeast is a micro organism.  It is in the air and on every surface - it is all around us and it's job in this world is to break things down in a process of fermentation.  It eats things and, just like humans, it emits gas in the form of carbon dioxide as a result.

Yeast's favourite food is sugar and it loves to eat the sugar in fruit, grains, flour and just about anything.  Hence, if you add sugar to yeast when you are proofing it, the bubbles and beige sludge appear more quickly and the bread baking process is faster.  For industrial bakers this is good: it gets the product out the door even faster.  The same is true for brewing.  If you add sugar in your brewing process, the product is ready more quickly (and you get more of it through your factory faster).  As a point of interest, there are only four countries in the world that forbid the use of sugar in beer brewing.  Can you name them?  Prize for the first person to respond with the correct answer!

No.  In fact there are different kinds of yeast for brewing different kinds of beer, for making different kinds of wine, for "nutritional" purposes, and for baking.  In spite of this, there are surprisingly few different kinds of yeast in the world.  To learn more about yeast you can do no better than have a look at Cara Technologies web site where you will find lots of info about yeast.

Until the 1850s we could not see yeast.  It was then, in a lab, that clever scientists cultured yeast so that we could actually see it.  Until then, therefore, all bread was baked with a sourdough culture which is no more and no less than yeast trapped in a paste of flour and water.  That is the first form of yeast:  it is trapped in a paste of flour and water.  We cannot see the yeast, but we know it is there because when we add flour and water to it, it bubbles.   Today some people call this form of yeast "wild yeast" or "natural yeast".  The other forms of yeast are all visible.  They include fresh yeast (it looks like a beige eraser and is crumbly), dry or dry active yeast (it looks like little round pellets), and instant or "easy bake" yeast which looks like a powder.  See the photos below:

Dry Yeast - notice it looks like small pellets

Fresh Yeast - notice it looks like a beige eraser

Instant or Easy Bake yeast - notice it looks like a fine powder

That entirely depends.  Using yeast in a sourdough culture is a specific form of baking.  It is not difficult or complicated it is just different and it takes longer to bake bread this way and the bread you make is a little different from bread to which you have added one of the other forms of yeast.  You can read more about sourdough baking here and you can come on a sourdough class with us if you get really interested.  Regarding yeast you can see, you are frequently limited by where you live.  In some parts of the world, fresh yeast is sold everywhere.  In other parts of the world, including the UK, it is harder to buy.  In some parts of the world dry yeast is impossible to find and instant yeast is everywhere.  So the first rule of yeast is "use what you can get".

If you can get more than one kind, you face a convenience versus purity conflict.  Fresh yeast is 100% yeast and you just crumble it into your flour, add everything else, and get kneading (convenient and pure).  Dry yeast is 100% yeast but you have to "proof" it (fancy word for dissolve in water) before you can use it because the pellets are too big to break down in the ordinary kneading process .  The result is that it does not work very well and you risk biting into a nasty tasting little pellet of yeast in your final loaf (less convenient and pure).  Instant yeast is instant.  Like fresh yeast, you just measure it into your bowl with all the other ingredients and begin to knead.  However it is not 100% yeast.  It contains additives (read the label - some instant yeast brands are 93% yeast and 7% additives) and this is simply something you should factor into your decision making process if you have a choice (convenient and impure).

My favourite kind of bread is sourdough bread because I like the flavour and the texture.  When I am using "yeast that I can see", my preference is for fresh yeast if I can get it.  This is because it is both convenient and pure.  If I cannot get it, I switch to dry yeast and simply have to accept the bread making process will take 15 minutes longer.  As a last resort, and when I teach, I will use instant yeast if I have to.  There is no time in a class to spend the extra 15 minutes proofing dry yeast.  However, it really is as a last resort because I don't want to ingest the additives if I don't have to.  Nor do I want to feed them to my students!

The three forms of yeast "that we can see" (fresh, dry, instant) are completely interchangeable.  However, you use different amounts of them, for the same amount of flour.  As a rule of thumb, the amount of dry yeast you need is 1% of the total amount of flour.  The amount of instant yeast is 50% of that and the amount of fresh yeast is double that.  Thus, if you are using 500 g of flour, you need 5 g dry yeast, 2.5 g instant yeast and 10 g fresh yeast.  This is fine if you are weighing your ingredients.  It's not so find if you are not.  However, every recipe should tell you how much of what kind of yeast you need.  If your recipe book does not tell you how much of what type of yeast to use, you can usually estimate by looking at the quantity of flour.  Calculate the percentage of yeast you are asked to use and take your best guess.  If it is 1% of the flour, it is dry yeast.  More than 1%, fresh yeast.  Less than 1% instant yeast.  And now, with the handy guide above, you can calculate how much you need of the yeast that you have.  In my book, All You Knead Is Bread, every recipe gives you the exact amounts of instant/dry/fresh yeast you need to use, and how to use them.

That depends what you mean by fail.  If you use too little yeast, your bread won't rise very much and it will take a long time to do very little.  If you use too much your bread will taste unpleasantly yeasty.  The important thing is that we just don't need more yeast than we need.  It's like salt.  A little is fine.  A lot is not.  Don't be tempted to throw a huge amount of yeast in your bread to make it really high!  It won't taste nice and it's not good for you.  Just stick to the guidelines above and you will be fine.