Rehydration of Yeast.

[yardglass]

hi all,

searched this and only came up with a few, so to clarify, would the following be ok ?

23gm in 100ml warm water 30min before pitching?

should i cover it with some glad wrap?

you'd think I would know this by now, will get my $hit together and do a starter next brew.

thanks
yard

[db]

yardy check out -

http://brewery.org/library/yeast-faq.html#part_one

when i re-hydrate i do 10-14g (for ales) in 100-150ml of pre-boiled water (around 30deg) in a sanitized cup.. i usually only stick a clean tea towel over the top. the glad wrap is a good idea tho - i'll be doing that next time

[Dogger Dan]

Gee db,

I don't even do that, it sits open while I am slopping the goods around

like the plaxtic wrap idea thanks

Dogger

[ausdag]

When I rehydrate the kit yeast I just add the yeast to half a glass of tepid tap water which has had a bit of sugar dissolved in it and then covered with gladwrap and within 10 minutes the yeast is expanding merrily and if it gets too warm I sit it in the fridge while I'm mixing the other bits and pieces in the fermenter.

Cheers,


DavidG

[Beerpig]

Slight side track ................. Excuse my ignorance

What are the advantages of rehydrating yeast?

Cheers

[Chris]

Beerpig, it reduces the initial lag time of the yeast replication process- ie the yeast starts faster.

Ausdag, that is fine, just don't add the sugar. I would explain why, but certain people seem to have a problem with my explainations. Just take my word for it.

[yardglass]

No Problems here Chris,

do tell.

thanks
yard

[Chris]

Ok, to rehydrate yeast, you need to put into warm water for aroud 15 minutes. This gives the yeast a good chance to draw in water across their cellular membrane, and hence restart their metabolic process. If the sugar levels are too high, then the yeast may be unable to do this.

Next stick a bit of your wort into the yeast/water mixture (after the 15 minutes), and watch for 20-30 minutes to see if the yeast has swollen up, and started foaming a little. If so, add it to your wort. If not, ditch the yeast and start again.

This process reduces overall lag time, by kickstarting yeast metabolism, but it also reduces the strain on the yeast by reducing thermal shock.

[yardglass]

thanks Chris,

informative as usual.

yard

[ausdag]

Ausdag, that is fine, just don't add the sugar. I would explain why, but certain people seem to have a problem with my explainations. Just take my word for it.

Okey Dokey....I'll leave the sugar out next time.

Cheers,
DavidG

[Chris]

You can add sugar later in the process to proof your yeast, but I perfer to use wort. It is just sitting there after all. It's just another way to reduce the chance of picking up bugs.

If you are just looking to rehydrate, don't bother. If you want to proof (which is often a good idea) then use wort.

[Dogger Dan]

Actually you can add a fermentable. The osmotic pressure required to negat the transfer of water across the cell membrane is large and additionally, as long as there is free water available (water not bound to the sugar) it will get it.

For example, Liquid Malt Extract. The reason you can store it on the shelf is because the water activity is so low nothing can grow in it. As Chris has pointed out there is insufficient water available to hydrate the yeast. We add water to make it fermentable which means the additional water we add can hydrate the yeast as it is not bound to the sugar

Regular wort will do as a starter, you wont need to do an additional hydration step.

Dogger

[GT Al]

If you want a good starter then try 2 tablespoons of dry malt (light) in 1 cup of hot water, cool it down to about 28 degC and add to a stubby with about 1/2" of beer and sediment (yeast), stopper with an air lock. Or 1 cup dry malt into 1.5lts of hot water (cool......etc;) put in a serilised 'goonie' with air lock, should start after 12 hrs or so. Pitch 1 lt of liquid, stir it up well to get a good dispersal of yeast, keep remaining 0.5lt in fridge for next brew.

[Kippo]

One question. Does rehydrating the yeast enhance your brew or does it just decrease the lag time, and if a recipe says to rehydrate the yeats, is it essential to do it? From what i have heard the only thing that rehydrated yeast does is decrease the lagtime and does not actually enhance the beer. If i ignore the 'rehydrate yeast' instruction is that a big problem?

Cheers!

Kippo.

[JaCk_SpArRoW]

From what I've read Kippo, rehydrating yeast is much better for fermentation as the yeast is already working when you put it in the wort, hence a much faster fermentation start...this is one of the main reasons I am assuming people use liquid yeast starters to give the best chance of the yeast doing what its supposed to.

[Kippo]

Yep just came across a post by 'Chris' that i seemed to have missed earlier. Since you rehydrate the yeast in warm water, does this mean that water and all is added or do you somehow drain the water from the yeast?

From what i gather you add it all but i want to be extra sure.

Kippo.

[JaCk_SpArRoW]

Nope, water & all mate...just pour it in, give a gentle stir...1 revolution should be sufficient...but make sure the water you rehydrate is closer to 30*C, not 40*C...I was told last night that 40*C is a bit warm & you will kill the yeast!

[Kippo]

OK sounds like a plan. Dunno when i am gonna do my next brew. Will be busy from next week onwards with tafe starting and all and work and i have another factor to contend with . NOWHERE TO PUT BEERS! Thinking of buying a largish wine rack to put them in. Planning to get another one cranking in no later than a month. If later i may go insane!

Cheers Kippo.

[JaCk_SpArRoW]

Let me give you some facts regarding rehydration and you can decide for yourself where you want to compromise. Every strain of yeast has its own optimum rehydration temperature. All of them range between 35°C to 40°C. Most of them closer to 40°C. The dried yeast cell wall is fragile and it is the first few minutes (possibly seconds) of rehydration that the warm temperature is critical while it is reconstituting its cell wall structure.

As you drop the initial temperature of the water from 35° to 30° or 25° or 20°C the yeast leache out more and more of its insides damaging each cell. The yeast viability also drops proportionally. At 35° - 40°C, there is 100% recovery of the viable dry yeast. At 15°C, there can be as much as 60% dead cells.

The water should be tap water with the normal amount of hardness present. The hardness is essential for good recovery. 250 -500 ppm hardness is ideal. This means that deionized or distilled water should not be used. Ideally, the warm rehydration water should contain about 0.5 - 1.0% yeast extract

For the initial few minutes (perhaps seconds) of rehydration, the yeast cell wall cannot differentiate what passes through the wall. Toxic materials like sprays, hops, SO2 and sugars in high levels, that the yeast normally can selectively keep from passing through its cell wall rush right in and seriously damage the cells. The moment that the cell wall is properly reconstituted, the yeast can then regulate what goes in and out of the cell. That is why we hesitate to recommend rehydration in wort or must. Very dilute wort seems to be OK.

We recommend that the rehydrated yeast be added to the wort within 30 minutes. We have built into each cell a large amount of glycogen and trehalose that give the yeast a burst of energy to kick off the growth cycle when it is in the wort. It is quickly used up if the yeast is rehydrated for more than 30 minutes. There is no damage done here if it is not immediately add to the wort. You just do not get the added benefit of that sudden burst of energy. We also recommend that you attemperate the rehydrated yeast to with in 2°C of the wort before adding to the wort. Warm yeast into a cold wort will cause many of the yeast to produce petite mutants that will never grow or ferment properly and will cause them to produce H2S. The attemperation can take place over a very brief period by adding, in increments, a small amount of the cooler wort to the rehydrated yeast.

One very important factor that the distributor and beer maker should keep in mind is that Active Dry Yeast is dormant or inactive and not inert, so keep refrigerated at all times. Do not store in a tin roofed warehouse that becomes an oven or on a window sill that gets equally hot.

Active Dry Yeast looses about 20% of its activity in a year when it is stored at 25° C and only 4% when refrigerated.