Rehydrating Dry Yeast?

Not to split hairs, but the scientific evidence you cited said, in effect, 'it depends'.

The bottom line is that, in my opinion, while there may be measurable differences in varying pitch rates, specifically to the extent that it determines whether or not to rehydrate dry yeast, the practical differences, in the context of homebrewing, are insignificant enough to be irrelevant. Rehydrate, if you like, or pitch dry, if you're so inclined. There's no scientific evidence that I'm aware of that says anybody will be able to tell the difference.

Going off on a slight tangent, the effect of pitching rate is much more easily observed when making bread, where yeast definitely translates to faster fermentation. But, as anyone who has made more than a few loaves of bread knows, if you're not in a hurry, slower is almost always better.

 

If there was nothing to be gained by re-hydrating, then it would make no sense to provide re-hydration instructions. The instructions would be "Just dump the dry yeast in the wort. It will make beer."

 

It just so happens that 11 out of 11 strains fermented faster with higher pitch rates. Did you miss that fact while you were searching for a sentence to cherry pick and validate your confirmation bias?

 

Actually, there is scientific evidence that contradicts your claim. If you can't tell the difference, then it doesn't matter to you. That doesn't mean it shouldn't matter to others who have more acute senses.

 

Just sayin' is all!

 

Yes, I've read and followed the dumbed down instructions on the package before. It made beer.

 

Jack, what is the recommendation for people who live in Portland OR with about 12 ppm TDS?

Hardness of 250-500 ppm? Me thinks the doctor is not into water chemistry, far from "normal", whatever normal is.

 

Some general comments. Brewing with some pros, I have seen one sprinkle the yeast in, one other rehydrate. Both beers were fine. Those were 500g bricks for a 7 bbl batch.

From making mead, where there is a lot of reason to have healthy yeast, and knowing some excellent pro mead makers, the procedure is to rehydrate, and use Goferm to get the yeast ready to head into battle.

For small beers I have sprinkled. For big beers and mead I rehydrate and use Goferm. I can't defend either technique, but those seem to work.

 

Jeff, I am not a yeast microbiologist so I have no comment here.

Maybe you could shoot a message to Dr. Tobias Fischborn at Lallemand/Danstar. He has responded to a number of my queries.

Cheers!

Jack

 

I think they would say to add some CaCl2 or gypsum to increase the mineral content. Or some Goferm.
http://www.morewinemaking.com/public/pdf/whydra.pdf

 

I hydrated US-05 once, it made no difference in the beer over dry pitching. My dry pitched normal gravity beers come out great.

 

So, I finally sat down (in my lab coat) and read this paper. Given the context in which the OP started the thread, I feel it's worth pointing out a few things which might not be immediately apparent to a new brewer:

1. The study looked at 11 *lager* yeast strains (important because lager pitching rates are universally higher than rates for ale yeast).

2. Even taking #1 into account? The 'normal density' pitching rate of 20 million cells per mL cited by Verbelen, et al. far exceeds the dosage instructions provided in the tech sheet for Fermentis W34/70 for pitches @ 15C.

Fermentis claims "*when dry yeast is pitched at 100 g/hl i.e. > 6 x 10^6 viable cells / ml*"
They recommend 80 - 120 g W-34/70/hl for pitching temps of 12 - 15C.
Verbelen et al fermented their wort at 15C.

Given this info, and the assumption that Fermentis' viable cells claim is accurate - lets go with Fermentis' high side:

120 g/hl = 1.2 g / l
5 gallon homebrew batch = 18.9 L
18.9 L * 1.2 g/L = 37.8 g of W-34/70 in 5 gallons (just to hit 7.2 million cells/mL)

Put another way? The 'normal' rate cited in the paper (20 million cells per mL) is ~ 2.8X higher than the high end of the range prescribed by Fermentis and is the equivalent of more than nine (9!) 11.5 gram sachets of W-34/70 in a 5 gallon batch.

The HD pitching rate? 4X higher. So, umm, 36+ pkg of yeast in 5 gal?

[head scratch]

I don't know anyone who routinely uses 9 pkgs of yeast in 5 gallons of wort - let alone 36 (and we all know that NO ONE ever makes starters for dry yeast because the SKY WOULD FALL! [sic]) - so, whether one rehydrates perfectly and recovers every last cell packaged or not? No one is hitting either of these pitching rates - least of all a new brewer pitching a pack from a kit.

Sometimes I rehydrate. Sometimes I don't. In either case, I've never used nearly that number of packs.

Does pitching more yeast result in faster fermentations (all else equal) - yes. Is faster always 'better' - commercial throughput aside? Subjective, inconclusive and strain-dependent.

 

Sorry... monday morning calculator typo/brain fart and it's too late to edit...


18.9 L * 1.2 g/L = 23.88 g (*not* 37.8)

That makes it 2.78 * 23.88 g = 66.3 g = a little less than 6 packets (not 9) in 5 gallons to hit 20 million cells per mL and 23 pkg in 5 gallons to hit 80 million cells/mL.

However, the general point I was trying to make remains the same.

For a 15 Plato wort? Even the LD rate is overkill, and 4X overkill (unsurprisingly) = 2-4X FASTER - but so what?

I'd be interested to see a similar study where the pitching rates more closely resemble those typically used by homebrewers. That is, something like 6 million cells per mL (fermentis label claim) versus 3 million cells per mL (50% of LC, if we assume abuse by lazy homebrewers results in 50% kill rate).

What, then, would be the difference in lag/fermentation time? Doubtful that it's linear...

 

.
Well, actually , I do all 3. Pour dry, rehydrate and make starters when the spirt moves me. I did not know there was an issue with dry yeast starters

 

@DunkelFester, maybe I am missing something here?

Fermentis recommends for W34/70: “They recommend 80 - 120 g W-34/70/hl for pitching temps of 12 - 15C.”

Assuming a batch of beer is 18.9 litters then there are 5.29 batches in 100 hl.

So if we divide the values above by 5.29:

· 80g/hl ÷ 5.29 = 15.13 grams

· 120g/hl ÷ 5.29 = 22.68 grams

So it would appear that a single packet for an 18.9 gram batch would be under-pitching but using 2 packets (11 grams x 2) would be about at the high end of the recommended pitching rate.

I have never brewed using dry lager yeast (e.g., W34/70) but if I did I would choose to use two packets (the old rule of thumb of pitching double the amount for lagers vs. ales).

Cheers!

 

What you have here is correct, Jack - if following fermentis' instructions. As an aside, I've used 34/70 according to the recommended dosage many times with great results.

As for the outrageous number of packets I mentioned? Those are what you would need to use *if* you took what the authors of the paper BrewBetty shared called 'normal pitching rate' to be, well, 'normal'.

http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2008.tb00317.x/pdf

I was just attempting to point out that 20 million cells per mL is anything but 'normal' for a 15P wort at 15C. While not *grossly* overpitching, it's arguably 2X what is necessary - even for a lager. Then they compare this to a pitch rate 4X higher still

 

The only point of linking the study was to illustrate more yeast ferments faster. If anyone has scientific evidence that contradicts this fact with any yeast under any condition, please submit a link to the study.

Again, faster doesn't necessarily mean better, but it does mean MH was wrong. #winning

I sometimes wonder if the no re-hydration people don't do a starter with liquid yeast just to keep their pitch rate consistent with their dry yeast pitch rate. Or maybe they don't do a starter because it makes beer? Who knows? Not me.

The majority of the time a brew noob gets stuck at a higher than expected FG, they didn't rehydrate or they didn't do a starter for liquid yeast. In both cases, they didn't pitch enough yeast. However, you can still majorly underpitch and finish at the right FG. If it was consistent, there would be a lot less threads about 1.055 OG beers getting stuck at 1.020.

 

'More ferments faster' still applies, but to an ever-decreasing degree once you have enough yeast present - whether you call that amount 'optimal' or 'normal pitching rate' or whatever. Point being that there is, practically speaking, a point where pitching "more" (even 10x more) won't result in faster ferments that are *detectable* (or of any benefit) to the non-labcoat-wearing homebrewer.

http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1970.tb03311.x/pdf

"At normal pitching rates (approx. 1 lb./ barrel) the ability of the yeast to utilize maltose was high and was maintained at high level over most of the period of maltose utilization. As the amount of pitching yeast was increased (to 2 and 4 lb./barrel) so the activity of the yeast fell, although the reduced activity was still maintained over most of the period of maltose utilization. When the amount of yeast pitched was reduced from 1-0 lb./barrel to 0-5 lb./barrel the plateau of activity was shortened and at 0-25 and 0-1 lb./barrel became progressively sharper peak which moved gradually to an earlier stage of the fermentation. After the initial peak, when using low pitching rates, the effectiveness of the yeast toward maltose fell rapidly and remained low throughout the remainder of the fermentation.

The changes in yeast activity with pitching rate could be due to differences in the degree of stirring by carbon dioxide bubbles, resulting in different proportions of active yeast in the population being kept in suspension. It is known that the overall rate of wort fermentation is affected by the ability of the yeast to ferment maltose4 at standard pitching rate. Thus the changes in activity of the yeast just described are reflection of the disproportionate changes in fermentation time shown in Figs. and 2.

There is only small decrease in time of fermentation at high pitching rates since, although much larger amounts of yeast are present, it is of reduced effectiveness. Similarly, when amounts of pitching yeast below the optimum were used, the marked slowing of fermentation was due not only to the low amount of yeast present (Fig. 3) but also to that yeast which was present having only low activity throughout the bulk of the fermentation despite high activity for short period. It appears, then, that if normal amounts of yeast are pitched, the growth of yeast (Fig. 3) and the ability of the yeast to ferment maltose (Fig. 6) are both at their fullest expression. Deviations result in loss of efficiency which is only partly compensated for by changes in the amount of yeast used. Maltase activity of the yeast was estimated throughout fermentation in the cases where more than 0-5 lb./barrel of yeast was pitched. The patterns and levels of activity were closely similar for the different pitching rates and, in accordance with earlier results,4 maltase was found to be present in excess throughout the fermentation."

 

My work is done here.

 

http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2008.tb00317.x/epdf

This study was interesting considering I just brewed 2 batches with 34/70. The first was a German Pils (2 older sachets...thanks Morebeer) that initially seemed OK, but POST-fermentation developed god-awful levels of diacetyl...even after conducting a drest. I fermented @ 52*F which was substantially lower than the study's 59*F. I may never us 34/70 again, but if I do it will be @ closer to 60*F than 50*F. Never had this problem with diacetyl before with lagers. Second batch was a 1.082 Baltic Porter pitched on the entire cake from the Pils...that one seems fine, but haven't sampled lately.