How I Rehydrate Dry Yeast In Ten Easy Steps

[mobrien]

I've seen the questions "how to I rehydrate yeast" asked a few times - so since I'm using a dry yeast today with an aussie ale, thought I would document the process.


Step 1.

Choose a good yeast. If you are using a kit, ditch the yeast its probably been in the lid for years and heated/cooled hundreds of times! Buy a good yeast!

Some good brands (and there are others of course!):

Fermentis Safale, Safbrew and Saflager
http://www.fermentis.com/FO/EN/06-Ales/90-10_product_cb.asp

Lalvin a wine yeast manufacturer that does some beer yeasts such as Nottingham
http://www.lallemand.com/Brewing/eng/aboutus.shtm#product

Brew Cellar
http://craftbrewer.com.au/index.php?page=s...t&Itemid=29

 

[mobrien]

Step 2.

Find the specifications for your chosen yeast there are usually FAQs, datasheets or PDFs on the website of the manufacturer or supplier.

What you really want to know is What temperature should I rehydrate this yeast at.

For this photo tutorial, well be using a Fermentis Safale US-56.

According to the PDF, it should be rehydrated in 10 times its own volume of sterile water or wort at 27 degrees +/- 3 degrees.

 

[mobrien]

Step 3.

Find a nice clean container to rehydrate your yeast in. I like to use beer glasses.

Step 4.

Clean your glasses, yourself and everything that will come into contact with the yeast. I use Idophor made up in a spray bottle. This means I can spray everything, and know I kill most of bugs. This is sanitising, not sterilising I cant be sure I kill everything. As a note, clean the spray bottle too no point in cleaning everything, and then getting dirty hands from the spray bottle!

 

[mobrien]

Step 5.

Even though idophor is a no rinse sanitiser, I rinse it out with boiling water when making a starter. Why? I dont want to kill any yeast, and Im using boiling water anyway!

Rinse out the glasses, then drain.

 

[mobrien]

Step 6.

I like to use a mix of water and wort the argument here is it is easier on the yeast to start, as it is dilute, but you are training it on the actual wort you will pitch it into.

Edit:
Please note: Some people believe that yeast should be hydrated only using water, because of the osmotic pressure in a wort solution. I don't agree, so this is the way I do it. You have been warned! For a full description of why you should or shouldn't use wort in the rehydration, there are posts at the end of the steps adressing both sides.

Fill the glasses with boiling water, and then top up with chilled boiled water to about .



Then using some wort from the fermenter, fill the glass.



At this point you want to measure the temperature you need a decent thermometer! You are aiming for a few degrees above your target, to allow time to get yourself sorted out.

 

[mobrien]

Step 7.

Cover the whole setup with glad wrap this stops any airborn bugs! Now wait for the correct temperature.



Since the temp range for the yeast I am hydrating is 27 degrees +/- 3 degrees, it means I can pitch anywhere from 24 to 30 degrees. As I know it will cool during the hour long process, I like to pitch at the top end of this range around 29 degrees. This means over the time it will drop to pretty close to the wort temp.

 

[mobrien]

Step 8.

Once it is at pitching temp, sprinkle the yeast VERY SLOWLY while briskly stirring the mix. You need to dissolve each individual particle of yeast and not get clumps. It should take about 1-2 mins for a 11g sachet.



After its all dissolved, you probably will get a bit of froth on top



Now cover and wait for 15-30 minutes.

 

[mobrien]

Step 9.

You should now have a nice cup of frothing yeast.

After 5 minutes:


After 15 minutes:



You want to stir it about every 5 minutes for then next 30 minutes. By now it should smell, well. Yeasty! You can actually hear it bubbling and watch the froth grow. Ive had these fire so well I have to stir every 2-3 minutes so as not to froth over the top of the glass! Always recover the glass with gladwrap in between each stir you still dont want airborn nasties in there!

After stirring:

 

[mobrien]

Step 10.

By now you should have a nice creamy glass of yeast! This may take longer with some yeasts or on a cold day. Open your fermenter, pitch while stirring (pretty much the same as when you dissolved the yeast in the starter) - Remember to sanitise your spoon first (remember the idophor spray).



Close the fermenter and add airlock/blowoff tube. Nowadays I use a dilute idophor solution in my airlocks it is easy to see the level, and if there was any back pressure, the liquid going in should be sanitised. I also leave a tuppaware container of idophor in the fridge to wash/rinse hands etc.



All done hope this is useful!

 

[bindi]

I use only pre boiled water to rehydrate dry yeast and start feeding it wort after about 20 min if I have to wait to pitch it.
Something about Osmotic pressure <_< . I will let the gurus explain.

Edit: Fermentis Site here on how to rehydrate dry yeast.

 

[dr K]

I use only pre boiled water to rehydrate dry yeast and start feeding it wort after about 20 min if I have to wait to pitch it.
Something about Osmotic pressure <_< . I will let the gurus explain.

Edit: Fermentis Site here on how to rehydrate dry yeast.

Bindi is quite correct. The idea of rehydating is exactly that, to replace the water by absortion through the cell walls, the osmotic pressure of a sugar solution will cause stress and death.
Ahh...but you say, commercial breweries often pitch dried yeast direct into a sugary wort !!
If you look at the various dried yeast sites (or read the instructions on a 500gm pack) you will find that the pitching rate for ale (assuming fresh yeast) fresh yeast is 1gm per litre and for lagers about twice that so for 25 litres of lager you really need 50gms of dried yeast!!.
Of course you only need one cell of your yeast to start fermentation, its all about competition. Correct rehydration of dried yeast will give your yeast a much better chance.
Anyway mobrien, edit out the wort and you have a great post !!

Kurtz

 

[normell]

Thanks mobrien, but is it really necessary to re-hydrate dry yeast ?? :blink:
I've done 30+ brews, all using Saf yeasts, both Ale & Lager, and always just "sprinkle" onto the wort.
Not one failure yet

Normell

 

[mobrien]

Hi guys - glad I started some healthy discussion! Ok - I'll respond in order

Bindi and Dr K

Whilst I understand where you are coming from, I'm not going to edit my post, nor will I be changing my method. This thread was a "this is how I do it" post - its up to you as to how you want to do it. I'm glad you raised your point of view though, as it will hopefully make people think about what they want to do and why.

Just for the record, I will give a rationale for why I do it my way.

As you both quite rightly point out, there is an osmotic pressure because of the sugars and other items in the wort. Wort at around 1.041 is the equivalent of a sugar solution of 67.4g/L. If we do the osmotic pressure calculation for this, we find the pressure is 4.9 atm - that is around 5x normal air pressure.

<geeky science calculation>

mass sugar = 67.4g
molar mass sugar (C12H22O11) = 342g/mol

therefore n(sugar) = 67.4/342 = 0.197 mol

Because we are talking about 1L (1000mL) the molarity of the solution is the same:

[sugar solution] - 0.197 M or 0.197 mol/L

Using P=MRT we can work out the pressure in atmospheres:

First 29 deg C = 302K

So:

P = 0.197 x 0.0821 x 302 = 4.9 atm

</geeky science calculation>

This is quite a large pressure! its the same as the yeast being in water 39m deep! And yet, as you know, sprinkling yeast onto wort will work just fine (in fact, as you allude to, it is even on the instructions!)

However, I don't think this is a good idea. It stresses the yeast, and of course decreases numbers. In the end it will work, but I like to play the odds in my favour.

So in my case, I dilute the wort, using a 1:2 dilution, water to wort. Now using the same geeky calculation as above, but this time with 22.46g of sugar (1/3 wort), we find the pressure is now 1.6 atm. Now this is only the same as the yeast being 6m deep in water (coincidently about the size of the big industrial fermenters).

It still is a positive pressure on the yeast, but one I am willing to put up with - why? Well, yeast use both oxygen during aerobic respiration, and sugar during anaerobic respiration. Whilst we want aerobic respiration during the rehydration, as this encourages multiplication, it is very easy for the yeast to remove all the oxygen. When this happens, I want them to have a food store - and I have a choice - I can use DME, sugar or wort - I'll use the wort any day of the week.

Anyway, that is the logic and the science behind the way I do it - and it works for me!

Matt

 

[mobrien]

And now to reply to Normell,

Sprinkling the yeast over the top will work fine any day of the week. I've done it many times, and like you have never had a failure.

However, rehyrdating the yeast in a more favourable environment will get the active and ready to go a lot faster. This is for two main reasons. The first is they have absorbed the water, and so come "back to life" - when you add them to the wort, they are ready to go and more survive. The second (if you add sugar or wort either at the start or pretty soon into the rehydration process) is that you get the yeast reproducing (or well on the path to reproducing) before they hit the wort, so again, numbers increase.

A case in point - the two hydrated yeasts I made this morning for this thread were added at 10:00am or so. The airlocks were bubbling by 11:30. Dry yeast (in my experience) takes around 6-12 hours to do the same.

M

 

[normell]

points taken onboad mobrein, will buy a thermo tomorrow, and do your method for my next brew.
this Homebrewing caper is all learn, learn and learn some more

Normell

 

[Ross]

Adding wort will work, as will sprinkling dry, but for maximum viability & health of your yeast, JUST REHYDRATE WITH WATER.

cheers Ross...

 

[dr K]

Adding wort will work, as will sprinkling dry, but for maximum viability & health of your yeast, JUST REHYDRATE WITH WATER.

cheers Ross...

Ross
In one single line, what would have taken me 5 paragraphs !!!!

k

 

[mobrien]

But why? Where is your data?

For now, I'll keep on doing things my way - I'm happy to have my opinion changed, but "just do it this way" with no explanation or data won't go any way to changing my mind.

So I propose an experiment:

24 x 250mL conical flasks
4 concentrations of sugar - 0g/L; 22.4g/L; 44.8 g/L; 69.2g/L
4 packets of yeast
bung and delivery tube for each flask, to inverted water filled measuring cylinder

Pitch 1/3 pack of yeast (equal weight to 3 dec places) in each flask on 100mL fluid. 3 replicates of each treatment - i.e. 3 flasks 0g/L sugar; 3 flasks 22.4 g/L sugar; 3 flasks 44.8 g/L sugar and 3 flasks 69.2g/L sugar.

Measure the volume of gas produced over the rehydration time - since CO2 gas production is a known measure of yeast activity. This will tell us which one is the best for rehydrating.

After 1 hour, pitch 10mL of each of the hydrated yeast into 200mL of 69.2g/L sugar solution, and continue to measure CO2 gas production. 3 replicates of each again. This will tell us which is the best over time for fermenting.

I have the equipment to do this at work - so before I do, do the "anti wort" people have any problems with the experiment? What yeast should I use?

M (willing to test it all)

 

[bigfridge]

But why? Where is your data?

For now, I'll keep on doing things my way - I'm happy to have my opinion changed, but "just do it this way" with no explanation or data won't go any way to changing my mind.

So I propose an experiment:

Mobrien,

No need to test your theories as the research has all been done before by a leading yeast authority. See here for a full description of what happens when you re-hydrate dry yeast and why you should not use wort for the best results.

David

 

[Lindsay Dive]

Try Fermentis K-97.....only joking.
I reckon the test would be real interesting....go for it....use SO4.

Regards,
Lindsay.