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Yeasty Issues

"Tom" <sail_saba@cox.net>
Mon, 22 Jan 2007 17:15:31 -0700
v107.n004.5
I want to try to clarify some of the issues pertaining to 
yeast.  First, there are dozens of Genus of yeast, hundreds of 
species, and thousands of subspecies or strains.  All regular 
commercial baker's yeast (i.e., not specialty yeasts or sourdough 
starters) that you buy, are the species Saccharomyces 
cerevisiae.  There are numerous subspecies or strains of 
Saccharomyces cerevisiae (there are hundreds, and likely thousands, 
of different strains).

In commercial production, different strains are used for each of the 
following products:

1) Compressed Yeast [this includes liquid yeast cream, block and crumbled]
2) Active Dry Yeast
3) Instant Dry Yeast [in the USA brand names include Fleischmann's 
RapidRise and Bread Machine yeast and Red Star's (now SAF) Quick-Rise 
and Bread Machine yeast]

To complicate matters each company that manufactures these products 
has their own patented strain of yeast.  The patents on Compressed 
yeasts have long expired as have most of the Active Dry Yeast 
patents.  There currently is much patent activity in the Instant Dry 
Yeast category.  Here, each manufacturer has their own patented 
strain and composition.  They are creating many specialty yeasts now 
for specific applications.

For instance, a 1998 patent titled "Instant dry yeast for use in 
frozen dough-baking process" uses "a biologically pure culture of 
Saccharomyces cerevisiae P-572, FERM BP-6148" - this is the patent 
for this particular Instant Dry Yeast strain.  This Instand Dry Yeast 
has superior properties for use in frozen doughs (the yeast degrade 
slower and thus the frozen dough has a longer shelf life).

The manufacturing process (to produce the yeast you buy in grocery 
stores) is identical for all three strains of yeast (Compressed, 
Active and Instant) until the final stages.  The indredients used in 
the manufacturing steps are: the seed yeast culture, water, molases, 
different minerals and
vitamins, and oxygen.  In the end stages different processing aids 
are added that include: salt (yes, sodium chloride), oils, emulsyfing 
agents and other processing aids.  These processing aids help in the 
drying and extruding steps AND ARE NOT ADDED TO HELP IN BREAD BAKING 
OR ANY DOUGH HANDLING PROCESS.  These processing aids are in such 
small amounts that they do not need to claim them on the packaging label.

Some specific items:

Mike Avery wrote:

>I have to disagree here.  In the 1970's I read James Beard's "Beard 
>On Bread" and he said that active dry yeast was reliable enough that 
>proofing the yeast was a waste of time, and that he neither did that 
>nor recommended it.

In general this is true, if you are using fresh Active Dry Yeast and 
you go through your supply rapidly, you do not have to check that it 
is still alive (i.e., proofing).  However, if you did not store your 
Active Dry Yeast properly or it is just old you may want to check its 
activity by proofing before you make any bread.

Note:  If you are uncertain about your Instant Dry Yeast you can use 
the same technique to proof it to see if it is still alive.

Larry T wrote:

>Thank you for your clarification about the  types of yeast. I was 
>sure I had read somewhere that RapidRise was the same as instant, 
>but I couldn't find the source, after reading otherwise on this list.

You are correct Fleischmann's RapidRise yeast IS an Instant Dry Yeast.

JH wrote:

>Thanks to Maggie Glezer for her very informative comments on active 
>dry and instant yeast in bread-bakers.v107.n002.3. As she says, with 
>the appropriate volume adjustments, the home baker can substitute 
>active dry for instant (and vice versa) with equal results.

You can substitute fresh Compressed Yeast, Active Dry Yeast and 
Instant Dry Yeast in any situation.  The only real difference when 
used in baking is the number of viable yeast cells per 
gram.  Compressed Yeast contains about 70% water vs 7% for Dry 
Yeast.  The granuels of Instant Dry Yeast are smaller then the 
granuels of Active Dry Yeast and thus you can get more viable cells 
in the same volume.  The formula for substituting is as follow:

100% Compressed Yeast
  = 40-50% Active Dry Yeast
  = 33% Instant Dry Yeast.
or
100% Instant Dry Yeast
  = 1.2 - 1.5 times Active Dry Yeast
  = 3 times Compressed Yeast

>Basically, the cell membrane for instant yeast is thinner than that 
>for active dry. This allows instant yeast to absorb water readily so 
>it does not need to be dissolved in water.

I have not read or found any articles that discuss the cell membranes 
size (thinner in Instant Dry Yeast vs Active), can you share with us 
your source for this statement?

>Basically, the cell membrane for instant yeast is thinner than that 
>for active dry. This allows instant yeast to absorb water readily so 
>it does not need to be dissolved in water.

The problem of dissolving Instant Dry Yeast (and Active) in water is 
discussed in a yeast patent.  It reads:

"A problem encountered with Active Dry Yeast and Instant Dry Yeast is 
the leakage of yeast solids from the cells upon rehydration. This 
results in a loss of gassing power or a loss of capacity to produce 
ethanol. The various methods of adding yeast and mixing dough differ 
from country to country. Although for the more porous Instant Dry 
Yeast the dry yeast should be mixed with flour before water is added, 
it often happens that the dry yeast is suspended in water together 
with other soluble additions before flour is added. Additives such as 
sugar, calcium propionate and salt affect yeast performance, as does 
the temperature of the water employed.  In countries with warm 
climates or where bakers use high speed mixers with extra heat input, 
the water is cooled, for example by adding ice, to obtain proper 
dough temperatures after mixing. Under these conditions instant dry 
yeast comes in direct contact with the chilled water, thus reducing 
the yeast performance substantially. In U.S. Pat. No. 4,764,472 this 
problem is partly solved by the incorporation of 0.1 to 2% by weight 
of locust bean gum, gum ghatti and mixtures thereof, which prevents a 
loss of activity when water of about 20 degree C. is added. However, 
in practice, water of 15 degree C. or less, even sometimes a 
water/ice mixture, is used and under these circumstances, the 
activity after rehydration is extremely low."

This problem really only affects those that are adding Instant Dry 
Yeast to very cold water (and usually are large commercial 
bakeries).  The resulting loss of gassing power is probably so small 
home bakers would never notice it.

I was surprised to note a container of Fleischmann's RapidRise Bread 
Machine yeast has the following statements:

"Avoid direct contact with liquids and salts."

and then a little below says:

"Actived Dry Yeast Recipies: Combine 1/4 cup warm water and 1 tsp 
sugar. Add bread machine yeast [yes, this is the RapidRise Instant 
Yeast] and stir to dissolve.  No other changes are needed." - So much 
for avoiding liquids...lol.

>can damage or kill some yeast cells, as can direct contact with salt 
>in the dough. This is why recipes often recommend that instant yeast 
>be mixed in the flour first, then salt is mixed in and then the 
>liquid is added.

The salt action on yeast has been greatly exaggerated.  Dry salt in 
direct contact with dry yeast does NOT kill the yeast nor does it 
kill the yeast in the dough.  Short term contact such as the time 
your ingredients are sitting together in a bowl even if it is 
overnight is not a problem.  If you have any doubt do the 
following.  Using whatever method you use to proof your yeast, set up 
this experiment:  Using two identical containers (drinking glasses 
work well), in one empty glass place just the yeast (amount 
recomended for proofing).  In the other glass place the same amount 
of yeast PLUS the amount of salt that you add to one loaf of 
bread.  Let the glasses sit overnight at room temperature.  The next 
day add the same amount of warm water to each glass and stir in 1 tsp 
table sugar.  Both glasses will foam up an identical amount proving 
that contact with salt is not a problem for home bakers.

The conditions under which salt and yeast react detrimentally are not 
experienced by the home baker.  If a home baker made two identical 
loafs - one with salt and the other without salt - they would notice 
absolutely no difference in the process, the feel of the dough, the 
volume expansion during proofing, rise times, or in the appearance of 
the finished loaf. They may taste the difference but they would not 
feel or see a difference.

The only condition I can imagine is if a home baker wanted to store 
their yeast and salt together for a long period.  In this case, over 
a period of weeks and/or months the salt will extract the remaining 
7% water in the dry yeast - completely desiccating it and thus 
killing the yeast cells.  This process would take weeks and months 
before all the yeast cells were killed - not minutes or days.

>ADDITIVES IN INSTANT DRY YEAST: I buy my dry yeast in one-pound 
>packages. I notice that the ingredients listed on the package 
>include, besides yeast, ascorbic acid (vitamin C) and an emulsifier 
>(though both additives are in small amounts). My packages of SAF 
>Instant Yeast and Fleischmann's Instant Yeast both list the 
>following ingredients: yeast, sorbitan monosterate (the emulsifier), and
>ascorbic acid. In contrast, whenever I've purchased Active Dry yeast 
>(usually Fleischmann's) the package ingredients always just say 
>yeast (nothing else).

In the case of Vitamin C, although vitamin C is a dough enhancer, 
these companies are not adding it to their products to improve your 
dough - they add it to the yeast (especially Instant Dry Yeast) 
because it is also an anti-oxidant.  Most, if not all, of the dry 
yeast containers are packaged under an atmosphere of nitrogen - the 
intent is to displace air which contains oxygen.  Oxygen will 
eventually kill the yeast cells - it will oxidize them.  It is the 
same process when you see that fresh steak start to turn color - the 
meat is oxidizing.  Most containers say to use the dry yeast within 6 
months of opening.  Vitamin C acts as an oxygen scavenger thus giving 
the product a 6 month recommended use period.

Many Instant Dry Yeast products contain or will start to contain 
variations of the chemical Sorbitan Monosterate.  Again, this 
chemical is not added to enhance your dough in any way but is added 
as a rehydration-controlling agent.  From a yeast patent is the following:

"In EP-A0616030, Instant Dry Yeast is improved by adding a 
rehydration-controlling agent. A large variety of rehydrating 
controlling agents is suggested among which are esters of fatty acids 
(e.g. fatty acid esters of sorbitan such as sorbitan monolaureate, 
monopalmitate, monostearate or monooleate). Addition of sorbitan 
monostearate or glycerine monostearate resulted in an improved 
gassing activity of the Instant Dry Yeast when the yeast is 
rehydrated before being mixed with other dough ingredients such as 
flour, water, and salt. The disadvantage of these agents is that, 
although some improvement in the (cold) water resistance of the yeast 
is obtained, still too much gassing power of the Instant Dry Yeast is 
lost when the Instant Dry Yeast is subjected to rehydration."

Bob the Tarheel Baker wrote:

>No!  No!  No!  Rapid-rise yeast is not the same as Instant 
>Yeast.  RRY has chemicals added to it to make it rise in half the 
>time it takes for active dry yeast and instant yeast to rise.  In 
>addition, the yeast cells die quicker so there is really just enough 
>oomph for one rise. Rapid-rise should not be used by artisan bread 
>bakers who believe long, slow rises contribute both flavor and structure

Sorry Bob, RapidRise yeast is Fleichmann's brand of Instant Dry 
Yeast.  You are misinformed, RapidRise yeast does NOT contain any 
chemicals that are added to "make it rise in half the time for active 
dry yeast and instant yeast to rise."  The last time I saw one of the 
individual packets of RapidRise yeast the only ingredient listed was 
yeast.  It did not contain vitamin c (whose chemical name is ascorbic 
acid) as the individual packets are intended for a one time 
use.  Thus, they do not need to add an anti-oxidant since it is 
intended the contents would all be used at one time.  The 4 oz 
containers of Fleischmann's RapidRise list yeast and ascorbic acid as 
the only ingredients.

Please share with us any articles that back up your claim that 
Instant Dry Yeast "cells die quicker" - All strains of yeast, 
including Instant Dry Yeast, go through normal cell growth and 
reproduction as long as they have water, food, oxygen and the right 
temperature.  In bread dough they have all these ingredients.

RapidRise yeast can certainly be used by artisan bread bakers.  You 
simply use an amount equivalent to the amount of Active Dry Yeast or 
Compressed Yeast.  It is an easy substitution and you keep all other 
aspects of your recipe and process the same.  Your dough will not 
rise faster - you can use all the same slow rise techniques that 
contribute to flavor and structure.

There are no magical ingredients in RapidRise yeast.  The name may be 
misleading but it is simply a tradename.

One source states that is takes 20,000,000,000 yeast cells to make 1 
gram (yes, that is 20 billion).  I do not know if that is in their 
fully hydrated stage or in their dried state.  The only real 
difference between Compressed Yeast, Active Dry Yeast and Instant Dry 
Yeast is the number of cells per gram.  Compressed yeast has the 
fewest and Instant Dry Yeast the most.  And what is important, is the 
number of viable cells you add in your recipe.  Be it Compressed 
Yeast, Active Dry Yeast or Instant Dry Yeast if you add the same 
number of viable cells you will get the same result.

Gloria Martin wrote:

>I do have a question. I know that salt inhibits the growth of yeast, 
>but I do believe I would like a little more salt in the finished 
>product. Would adding an additional 1/4 teaspoon inhibit the yeast too much?

Go ahead and add the extra salt if you think it will improve the 
taste. That small amount of additional salt will not impact the yeast 
in any way.

Tom