Tuesday, February 21, 2012
The Tesco Fast Action Dried Yeast can be easily found in some Tesco shop in Ireland.
If we look at the back of the packet we can read
"A blend of dried yeast with yeast improvers"
Emulsifier (Sorbitan Monostearate)
Flour treatment Agent (Ascorbit Acid)
It is pretty clear that what Tesco sells for dried yeast, it is actually a blend of yeast and dough improvers.
Let's look now at the action of each of them
Calcum Sulphate = pH regulator
Emulsifier (Sorbitan Monostearate) = It is a chemical that are soluble in both water and oil and should strengthen the dough and act as a rehydrating factor
Ascorbic Acid = It strengthen the dough as an oxidiser which encourages the formation of cross-bonds interlinking the gluten network.
Alpha Amylase = From wiki "Amylases find use in bread making and to break down complex sugars, such as starch (found in flour), into simple sugars. Yeast then feeds on these simple sugars and converts it into the waste products of alcohol and CO2. This imparts flavour and causes the bread to rise. While amylases are found naturally in yeast cells, it takes time for the yeast to produce enough of these enzymes to break down significant quantities of starch in the bread. This is the reason for long fermented doughs such as sour dough. Modern bread making techniques have included amylases (often in the form of malted barley) into bread improver, thereby making the process faster and more practical for commercial use."
While it is kind of common to find ascorbic acid in Instant Yeast or Calcium Sulphate, I don't think that the presence of Alpha Amylase make this yeast suitable for long fermentation dough I would not recommend using the Tesco Dried Yeast Blend for serious home baking.
Measuring and Weighting Tesco Dried Yeast.
After few empirical test, I found that the following inequalities hold true
tsp = teaspoon
2 tsp= 2 teasoopn
1/2 tps = half teaspoon
1/4 tsp = tad
1/16 tsp = pinch
1/32 tsp = smidgen
2 tsp + 1/2 tsp + 1/4 tsp + 1/16 tps + 1/32 tsp < 7gr
2 tsp + 1/2 tsp + 1/4 tsp + 1/16 tps + 1/32 tsp + 1/32 tsp > 7gr
2 tsp + 1/2 tsp + 1/4 tsp + 1/16 tps + 1/32 tsp + 3/4 * 1/32 tsp =~ 7gr
The first two tells me that a teapoon of Tesco Dried Yeast must be
2.43gr < tsp < 2.46gr
The third says that it is likely that 1tsp = 2.44gr
So if you want to measure up Tesco Dried-Yeast (which is a blend)
1 tsp = 2.44gr
1/2 tsp = 1.22gr
1/4 tsp = tad = 0.6gr
1/8 tsp = dash = 0.3gr
1/16 tsp = pinch = 0.15gr
1/32 tsp = smidgen = 0.08gr
1/64 tsp = drop = 0.04gr
So if you need to prepare a 12hr Poolish which requires 0.2% of fresh yeast for 250gr of flour, using a conversion factor of 40% from frest to instant you get
250gr * 0.2% * 40% = 0.2gr
You will need a Pinch + a Drop of Instant Yeast
Or if you don't have a drop (not easy to find here in the shops in Dublin)
a Pinch + half a smidgen.