What does dry yeast actually need when being rehydrated?

[Finlandbrews]

See all my questions below if you want to skip the background info.

I have been doing a few batches of 5 gallons with OG in the 1.050's and a pitch of 11.5 grams of hydrated safale 05 to find out after 2 to 3 weeks that my FG is stuck in the 1.020 to 1.025... I really don't understand why, I have fermented batches at 16 celsius and 20 celsius and it doesn't attenuate fully. Fermentis even says (although they don't specify for what wort gravity and fermentation temperature) that the packet of safale 05 dry yeast is good for 5.25 to 7.5 gallons batches.

I would like to attack the question of the vitality and viability of my yeast after hydrating as a potential solution to this issue. Actually my latest batch in question started fermenting very quickly seeing some Krausen already at 8-10 hours after pitching (the dry yeast packets were very fresh, I think two months after packaging with 2 years shelf life and was stored in the fridge). What I didn't pay very careful attention was the temperature difference between my wort and my hydrated yeast slurry (if we can call it like that for dry yeast being hydrated).

I understand the process should take 20-30 minutes and temperature of hydration should be around 35 degrees celsius. I understood also that distilled or bottled water is preferable as chlorine and other compounds that can be negative to yeast health such as iron and manganese have been removed.

Now my questions are:

1) should the yeast being rehydrated be in contact with air or would it be better to inject pure oxygen in the water and then seal the container in which the dry yeast is being hydrated?

2) what is the reason for the advice of not letting the dry yeast in water for longer than 20-30 minutes and not to use half litre of water for 11.5 grams of yeast instead? What do we risk by letting more time with big volume of water let's say one hour in half litre?

3) can the hydrating be more efficient by using a stir plate or adding yeast nutrient?

 

[kh54s10]

There is no reason to use oxygen, they say you don't even need to aerate the wort.

I'm not sure of the amount of water but the timing is that there are nutrients engineered with the yeast. After the 30 minutes the yeast are consuming this.

There is no need for a stir plate. In fact the directions for rehydrating say "do not stir the yeast into the water" Let it soak up the water and stir at about 15 minutes to make sure it all gets wet.

Add the nutrient to the wort, not the rehydration.

Are you doing extract brews? It is common for extract beers to stop at 1.020. It is due to the extract and not the yeast.
Rehydrate per the manufacturer's instructions. They have done the research as to the best process.

 

[specharka]

I think your problems stem from issues other than yeast hydration.
1) 16C/61F is on the bottom end of the yeast metabolic range. Even at 20C/68F I would want to raise the temperature after a few days to encourage attenuation.
2) Are you measuring the terminal gravity with a hydrometer or a refractometer? If using a hydrometer, is it calibrated properly?
3) What was the composition of the wort? 60% attenuation is pretty abysmal, but if there's a significant amount of unfermentables, I could understand.
4) Did you thoroughly oxygenate or aerate the wort? Thoroughly = 1-2 minutes with oxygen or 15-20 minutes with an aquarium pump.

There's other potential issues that you can troubleshoot, but none I know of are related to rehydration -- it looks like your rehydration process is sound.

 

[dcrog]

I'm pretty sure the 05 I pitched yesterday said to just sprinkle in wort.

(But what do manufacturers know)

 

[eadavis80]

I know many complain of 1.020 or higher FGs on extract brews, but I've not had that issue unless I add lactose which SHOULD have FGs of 1.020 or higher since that's non-fermentable.
My process when using dry yeast is as follows:
1. Boil up some tap water for 15 minutes on the morning of brew day. Let it cool and put it in a mason jar in the fridge.
2. Brew my beer.
3. Cool my wort.
4. Aerate my wort with a diffusion stone.
5. While it's aerating, I microwave some of the previously boiled water from the mason jar until it's about 100 degrees into a Prylex measuring cup. (takes about 25 seconds in my microwave. I also add a pinch of yeast nutrient to that water before heating it in the microwave).
6. Sprinkle dry yeast onto warmed water in measuring cup.
7. Cover with sanitized foil for 15 minutes and let sit at room temp.
8. Take temperature of yeast solution and if 80 or below, pitch yeast. If it's above that, I add in a little cold water from the mason jar until it's around 75 degrees (within 10 degrees of my wort temp).
9. Remove aeration stone from fermenter, pitch yeast.

 

[dmtaylor]

Rehydration has nothing to do with your problem.

My guess is that you might be using extract that contains too much unfermentable sugars and should simply try switching to a different brand of extract to see if the problem disappears. Or else trade some extract for a pound of sugar.

It is either that or maybe your hydrometer is reading too high. Test it in plain water and see if it hits 1.000. If not you need to subtract from every reading you ever take, past present and future.

 

[Pratzie]

Dry yeasts are packaged with basically all they need to get going. The water just rehydrates and makes them active. The 20-30 minute timeline is basically the window to get them up and running and ready to tear into some sugars.

With your other stalled batches, what temps are you fementing at and have you considered adding yeast nutrients during the boil?

And another stupid question but are u using a refractometer or a hydrometer to measure? As the poster above mentioned, make sure they are dialed in. You can test it using distilled water.

 

[Finlandbrews]

There is no reason to use oxygen, they say you don't even need to aerate the wort.

I'm not sure of the amount of water but the timing is that there are nutrients engineered with the yeast. After the 30 minutes the yeast are consuming this.

There is no need for a stir plate. In fact the directions for rehydrating say "do not stir the yeast into the water" Let it soak up the water and stir at about 15 minutes to make sure it all gets wet.

Add the nutrient to the wort, not the rehydration.

Are you doing extract brews? It is common for extract beers to stop at 1.020. It is due to the extract and not the yeast.
Rehydrate per the manufacturer's instructions. They have done the research as to the best process.

Thank you for your comments! No I'm doing all grain beer. I'm not sure about fully following the instructions of the yeast manufacturer though as they say pitch straight on wort and they give a very wide range of wort volumes that can ferment with one packet (20-30 litres) without mentioning gravity of wort or temperature while pitch rate depends on gravity of wort and fermentation temperature. Remember they try to sell and not over complicate as the most users of dry yeast are not super geeks and it sells better to have a easy to understand way of doing (but might not be the best).

 

[flars]

Don't use RO or distilled water for rehydrating dry yeast. RO and distilled water do not contain the minerals necessary to protect the yeast cells from being damaged by osmotic pressure.

Danstar recommends rehydration water temperature from 86°F to 95°F. Fermentis recommends 80°F ± 6°F.

Dry yeast should be stirred into the wort after 30 minutes when it is sprinkled dry onto the surface. This gives the yeast cells time to rehydrate.

I don't think the yeast is the problem. High FG could be from unfermentables in the recipe or even temperature fluctuations of the fermenting beer.

 

[ScrewyBrewer]

As I remember rehydrating a packet of dry yeast in a cupful of 35C/95F water is done to form a 'paste' that gets pitched into your wort. The temperature is recommended to allow the coating to become absorbent enough so that the cells can intake the water they need in about 20-30 minutes. Water will not be as damaging to the yeast cell walls than wort, that has something to do with the higher osmosis pressures of wort.

What does remain controversial though is agreement on the exact number of cells included in a standard 11g packet of dry yeast. Some manufacturers claim 6 billion cells per gram, while some yeast calculators default to 20 billion cells per gram. Then of course there are the differences in varying cell sizes for different strains of yeast. IMHO dry yeast is so inexpensive to buy that pitching another packet when in doubt seems to be the safer bet.

 

[h22lude]

A lot of good info here. I believe I read on Danstars site that they recommend 10 times the weight in water. So 115 grams of water to rehydrate in. Boil it for a minute or two. Let it cool to 85° and pitch. Stir after 15 minutes and again another 15 minutes later. Make sure it with 6° of your wort pitching temp.

Per Fermentis (I just emailed them about this), you DO NOT need to aerate wort when using dry yeast. If you do, it doesn't hurt but not needed.

 

[The_Bishop]

How are you measuring your final gravity? Hydrometer or refractometer?

 

[LBussy]

I use GoFerm for rehydrating all of my dry yeast, even those which "magically" claim to not need rehydration or other steps. To date, I have never experienced negative effects, and quite the opposite: in challenging batches such as Skeeter Pee my yeast appears to be exceedingly healthy and vigorous.

Another step I take is aeration. I use plain (filtered) air for at least 30 minutes pre-pitching, and continue aeration for a period of time (sometimes a few hours) after pitching to give the yeast the O2 they need at the time they need it. My belief is that continuing to add lower amounts of oxygen through the initial phases of yeast reproduction is more beneficial than a higher but singular dose of O2.

My results are not scientific but rather empirical. I developed this schedule over a few years after fighting with Skeeter Pee and now that I have a clean 5-6 day fermentation of that yeast-beating elixir, I am pretty confident that it's suitable for nearly everything. An exception may be something like a Weizen which relies upon yeast stress-induced by-products for the archetypical flavor profile.

Arguments against my process generally take the form of "the manufacturer says blah blah blah. My opinion is that a yeast vendor (they are not manufacturers, this is a living organism) can prepare yeast for a particular hardship such as de- and rehydration. They can include nutrients and precursors to give the yeast a head start. They can even include fatty acids which reduce the demand for things like oxygen. I also believe that it's going to be exceedingly difficult for me to be too nice to my yeast.

So, those are some musings based on my experience. It only takes an extra 20 minutes or so to rehydrate with GoFerm and of the maybe 30 batches I have done with various dry yeasts and Goferm, I've yet to have any issues attributable to the health or viability of the yeast. Take (or leave) it for what it's worth.

 

[Finlandbrews]

Don't use RO or distilled water for rehydrating dry yeast. RO and distilled water do not contain the minerals necessary to protect the yeast cells from being damaged by osmotic pressure.

Danstar recommends rehydration water temperature from 86°F to 95°F. Fermentis recommends 80°F ± 6°F.

Dry yeast should be stirred into the wort after 30 minutes when it is sprinkled dry onto the surface. This gives the yeast cells time to rehydrate.

I don't think the yeast is the problem. High FG could be from unfermentables in the recipe or even temperature fluctuations of the fermenting beer.

I ve used two pale ale malts for 75% of the grain bill with 25% Munich 10. Fermentation temperature has been stable around 16 degrees celsius. I wanted to ferment a bit lower because I had a rather strong phenolic character. Almost felt I used some Belgian yeast...

 

[flars]

I ve used two pale ale malts for 75% of the grain bill with 25% Munich 10. Fermentation temperature has been stable around 16 degrees celsius. I wanted to ferment a bit lower because I had a rather strong phenolic character. Almost felt I used some Belgian yeast...

I had brewed a dry Irish stout with US-05. Fermentation temperature was 63°F to 64°F. I had a very strong peach flavor in the stout. Same flavor did not show in hoppy beers brewed with the same yeast at the same temperature.

The next stout fermented at 67°F to 70°F with US-05 did not have the peach flavor.

 

[Finlandbrews]

How are you measuring your final gravity? Hydrometer or refractometer?

Indeed I should check with my hydrometer but my refractometer seem to be well calibrated! Maybe 0.002 error.

 

[ncbrewer]

Indeed I should check with my hydrometer but my refractometer seem to be well calibrated! Maybe 0.002 error.

A refractometer doesn't read right with alcohol in the mix. You can use an on-line calculator to make a rough adjustment, or use a calibrated hydrometer.

 

[TheFlatLander]

Another step I take is aeration. I use plain (filtered) air for at least 30 minutes pre-pitching, and continue aeration for a period of time (sometimes a few hours) after pitching to give the yeast the O2 they need at the time they need it. My belief is that continuing to add lower amounts of oxygen through the initial phases of yeast reproduction is more beneficial than a higher but singular dose of O2.

How are you doing this aeration? Would an aquarium pump, racking cane, tubing, stone and an HEPA filter work?

 

[pdxal]

Check the final gravity with a hydrometer next time. The refractometer reading needs to be corrected once alcohol is in the solution. There are several good refractometer correction calculators out there, I like Sean Terrill's.

 

[LBussy]

How are you doing this aeration? Would an aquarium pump, racking cane, tubing, stone and an HEPA filter work?

That is exactly how I am doing it. The stone is a SS 2 micron. I had to make a little adapter out of brass fittings to go from the aquarium pump size up to fit everything else, but other than that it was straightforward.