Yeast

 

I love the smell of freshly baked yeast bread, it is so welcoming. When bakers yeast (Saccharomyces cerevisiae) is added to bread dough the yeast uses sugar (fermentable sugars) as energy and during fermentation produces carbon dioxide and ethanol. It is the carbon dioxide that helps the dough to rise. Keeping your yeast growing is essential for good bread making. That means; feeding it, keeping it at a suitable temperature, ensuring there is sufficient moisture and not adding too many ingredients that inhibit its growth. If the growing conditions are optimal, a yeast cell can divide every ~ 100 minutes. However, the most important thing for bread making is the production of carbon dioxide by the yeast.

Feeding the yeast:

Like us, yeast requires glucose. If the available carbohydrate isn’t glucose (eg Sucrose) the yeast will convert it into the monosaccharides, glucose and fructose before it can use it as an energy source. Having some sugar (sucrose) in the bread dough will ensure the yeast is fed.  Other sugars that yeast can utilise are maltose (found in rice bran syrup) and fructose (honey and fruits).

If you don’t want to add refined sugar you can add other “sweet” things that can either be used by the yeast or converted into glucose then used. Roast pumpkin, sultanas, grated apple and honey are a few of the ingredients that could be used instead of refined sugar. If using an alternative sugar source be aware that you may need to increase the proofing time.

Temperature:

Yeast can grow through a range of temperatures (19o C – 36o C). They can grow outside this range but it is retarded at lower temperatures and the yeast is damaged at higher temperatures. But what is optimal?  The best temperature range for yeast to grow and divide is between 25o C and 27o C. However, the best range for the yeast to ferment, and therefore produce carbon dioxide and ethanol, is between 30 – 33o C.  What do we want the yeast to do, go forth and multiply or produce gas? It is most definitely the latter. Most of the bread made with Bakers' Magic Gluten free flour doesn’t need a long proofing time so having the dough at the higher end of the temperature range is okay.

Moisture:

Usually there is sufficient water present in the dough for the yeast to grow. However a skin can form on the outside of the dough if the environment that the dough has been placed in isn’t moist enough. There are a couple of ways of keeping the dough moist. You could use a damp tea towel or plastic cling film to cover the dough, alternatively place the dough in a warm oven with an open container of water.

Growth Inhibitors:

Sugar; although the yeast requires sugar too much will retard its growth. Increasing the amount of sugar in a bread recipe affects the final product. Prior to baking the dough will be stickier, the crumb (the appearance of the bread) will be smaller (the holes will be smaller), the crust of the finished product will be softer and be browner. So how much sugar is too much? If you take the amount of Bakers' Magic Gluten free flour as 100% then over 22% sugar is too much (For 450 g of Bakers' Magic Gluten free flour it would mean adding more than 100 g of sugar). I have tried up to 33% sugar basically the resulting bread is super sweet glug (not nice). The addition of ~ 17% sugar is okay (450g Bakers' Magic Gluten free flour and 75 g sugar) and I tend not to add more than this. If adding sugar greater than 22% I would put more yeast in.    

Salt; slows down (inhibits) the growth of the yeast and it also adds flavour. There have been a number of times when I am eating some bread and I realise I forgot to add the salt.  A longer proofing time may be required for breads that contain salty foods for example olives. I haven’t determined how much salt is too much as the thought of eating really salty bread does not appeal.  

Fats/Oils; can slow down yeast growth as well. However, when making bread with wheat flour fats/oils can help; to hold the structure of the bread together, tenderise the bread and preserve freshness. There are benefits in the final product when fats/oils (egg is included in this group) are added to Bakers' Magic Gluten free flour recipes as well. The addition of fats/oils; make handling the dough easier, gives the dough a nice gloss, and in the finished product gives a browner crust, adds flavour and reduces the size of the holes.