Rehydrate, or not to rehydrate, that is the question

[Paul Finney]

Hello all,

I tried trawling through the old posts but couldn't find it even though I assume it has been covered here before.

 

So what are people's thoughts on rehydrating dried yeasts before pitching? I have read lots of articles either way on this, and whilst direct pitching "kills" yeast (around 48% by what I have read), it doesn't seem to have any effect on my beers.

 

I direct pitch as I don't want to add another thing into my brewing day, especially one that opens up another route of infection if the process is slack.

 

Has anyone really noticed any difference with either technique?

 

Cheers

[Dunc]

My method: not sure whether it's right or wrong...it gets the airlock bubbling away within a couple of hours.

1/2 an hour before pitching (while my wort is chilling) Add 1 cup of cooled (room temp) boiled water and a teaspoon of white sugar to a sterilised container, cover with sterilised glad-wrap. Drop the yeast on top and let it sit for 10 minutes then just gently swirl. Keep it in a warm place. Give it a stir with a sterilised teaspoon. Pitch.

Works a treat.

[Ralph]

Paul you would do well to get a copy of the book "Yeast" and have a read. Yeast health has many different effects on beer and it may simply be that you are not quite picking up the difference in the brews that you are doing. If I use dried yeast I always rehydrate with water.

You could always split a brew and split a packet of yeast. Rehydrate one and not the other and see if people can pick a difference? Under-pitching (which is what is likely to happen if there are not so many viable yeast cells) can lead to a number of different flavours coming from the yeast. In some beers some of these flavours are desirable... in others they are not. 

The biggest difference will be if you want to repitch from the slurry. An initial pitch that is less than ideal might do an ok beer the first time, but if you repitch it is likely that the yeast health won't be good and subsequent brews will have greater and greater flavour changes from the yeast.

[Peter Smith]

+1 the book "Yeast"   for $30, this is one of the better buys.....

http://www.trademe.co.nz/books/nonfiction/cooking/other/auction-635...

[Paul Finney]

Cool, thanks for the heads up on the book, will have a look.

 

It seems that even the makers can't make their mind up. These are the instructions from the Fermentis website:

 

　

Sprinkle the yeast in minimum 10 times its weight of sterile water or wort at 27°C± 3°C (80°F ± 6°F). Leave to rest 15 to 30 minutes.

Gently stir for 30 minutes, and pitch the resultant cream into the fermentation vessel.

Alternatively, pitch the yeast directly in the fermentation vessel providing the temperature of the wort is above 20°C (68°F). Progressively sprinkle the dry yeast into the wort ensuring the yeast covers all the surface of wort available in order to avoid clumps. Leave for 30 minutes, then mix the wort using aeration or by wort addition.

If rehydrating in sugar solution, or a wort sample for that matter, aren't you "direct" pitching anyways?

[Peter Smith]

From the master Mr John Palmer

Preparing Dry Yeast
Dry yeast should be re-hydrated in water before pitching. Often the concentration of sugars in wort is high enough that the yeast can not draw enough water across the cell membranes to restart their metabolism.

I also think that Aeration of wort to get enough oxygen into it is  seriously mis-understood and not discussed enough online.

6.9.3 Aeration is Good, Oxidation is Bad

The yeast is the most significant factor in determining the quality of a fermentation. Oxygen can be the most significant factor in determining the quality of the yeast. Oxygen is both your friend and your enemy. It is important to understand when which is which.

You should not aerate when the wort is hot, or even warm. Aeration of hot wort will cause the oxygen to chemically bind to various wort compounds. Over time, these compounds will break down, freeing atomic oxygen back into the beer where it can oxidize the alcohols and hop compounds producing off-flavors and aromas like wet cardboard or sherry-like flavors. The generally accepted temperature cutoff for preventing hot wort oxidation is 80°F.

Oxidation of your wort can happen in several ways. The first is by splashing or aerating the wort while it is hot. Other beginning-brewing books advocate pouring the hot wort after the boil into cold water in the fermenter to cool it and add oxygen for the yeast. Unfortunately the wort may still be hot enough to oxidize when it picks up oxygen from the splashing. Pouring it down the side of the bucket to minimize splashing doesn't really help either since this increases the surface area of the wort exposed to the air. Thus it is important to cool the wort rapidly to below 80°F to prevent oxidation, and then aerate it to provide the dissolved oxygen that the yeast need. Cooling rapidly between 90 and 140°F is important because this temperature region is ideal for bacterial growth to establish itself in the wort.

In addition, if oxygen is introduced after primary fermentation has started, it may cause the yeast to produce more of the early fermentation byproducts, like diacetyl. However, some strains of yeast respond very well to "open" fermentations (where the fermenter is open to the air) without producing off-flavors. But even for those yeast strains, aeration or even exposure to oxygen after fermentation is complete can lead to staling of the beer. During racking to a secondary fermenter or to the bottling bucket, it is very important to prevent gurgling or splashing. Keep the siphon flowing smoothly by placing the outlet of the siphon hose below the surface of the rising beer. Decrease the difference in height between the two containers when you begin. This will slow the siphon rate at first and prevent turbulence and aeration until the outlet is beneath the surface.

To summarize, you want to pitch a sufficient amount of healthy yeast, preferably grown in a starter that matches your intended fermentation conditions. You want to cool the wort to fermentation temperature and then aerate the wort to provide the oxygen that the yeast need to grow and reproduce. Then you want to protect the beer from oxygen once the fermentation is complete to prevent oxidation and staling.

[Matthew Vincent]

Can someone please help me with the following? -

I've got a Dutch Pilsner and an American Lager (both William Warn kits).

My plan is to rehydrate 2 x Saflager S-23 sachets per kit and ferment them @ 12'C for a couple to 3 weeks.

What's the best method of getting the yeast down to around 12'C before adding to the wort? Cool the 'resultant cream' in the fridge for 30 mins(ish) or in a shallow cold water bath?

[Mike]

As far as I know cooling the rehydrated yeast quickly before adding to a 12C wort will have minimal effects, the yeast will still undergo a fast temp change so there's not much point. Fermentis recommends 23C rehydration and pitch straight in: http://www.fermentis.com/wp-content/uploads/2012/02/SFG_S23.pdf also if you can do one batch with 2x s-23 and one batch with 2x 34/70 @14-15C, compare the two. 34/70 is great. Alternatively, simply reuse the s-23 slurry in the 2nd batch (no starter required if re-pitched quickly) use the mr malty calculator to figure out how much slurry you need, assume thin slurry and over estimate slightly - you end up with a lot of cells and doing 4-5% beers like you are it's ideal. Have had good results with harvesting s-23 in the past.

[jt]

I've tried the rehydrate and the direct sprinkle - doesn't make any difference to me.

[Peter Smith]

I was over at deep creek and watched as a brewer sprinkled a box of yeast directly into a fermenter.....    I suspect the yeast was us-05 as he was doing an IPA for Beervana...

[Julian Melville]

I rehydrate in water as per the Fermentis instructions, haven't had any issues. I generally use water that was boiled and cooled.

[Mark Thomas]

It's funny, John Palmer reckons you need to rehydrate yeast, so I bung it into water at ~27deg and let it cream up for half an hour or so before pitching.  But I asked both Paul Croucher and Joe Wood at Beervana, and neither of them bother to rehydrate US-05 before pitching (they just sprinkle it on top of the wort).  So I guess US05 is robust enough to handle either method (at a rate of 1 packet per 20 litres or so).

[Ralph]

Another factor in the sprinkle or rehydrate will be the SG of the wort. A high SG might mean you need to rehydrate, where as a lower SG might be ok to sprinkle? High SG will mean less water available for the yeast to rehydrate properly.