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

[Crusader-Rob]

I rehydrate, It can't hurt a beer right. 

If there is a difference its not really noticeable to most people.provided you direct pitch enough yeast to start with anyway.

[jt]

But rehydrating doesn't increase the yeast count does it?

[Ralph]

no, but direct pitching may kill a number of yeast cells so rehydrating is likely to give you a larger number of viable yeast cells.

My comment about the high SG is that higher SG will make it harder for the yeast to rehydrate and so the effect of sprinkling yeast straight into a higher SG wort will be worse than a lower SG wort.

[Mike]

Although modern dry yeast have very high cell counts per pack I always rehydrate, it's especially important if you're nearing the edge of the pitchrate limit (or over) of 1 pack, or if the OG is high, as mentioned above. It IS another step in the process, which increases contamination chance, but the way I do it is pretty foolproof. Cup and a half or so of water in small pot with thermometer or fork, boil for 10mins, cool in sink to 20-27C, sprinkle yeast and stir with boiled/sanitised thermometer or fork, wait 10 mins, stir again, wait 10 more mins, stir and pitch. A clean dry yeast like US-05 can probably handle being pitched dry, as mentioned with the pro-breweries. What really matters is your cell count, they obviously had enough yeast for the batch, whereas your 11.5g pack of S-04 might struggle a bit in 25L of 1.065 stout wort - and rehydrating does give you more cells (some yeast don't rehydrate properly in the wort, some are sugar shocked and die, others are weakened). Of course, if you screw up the rehydration (too hot, leave it too long before pitching, contaminate the yeast etc) you can shoot yourself in the foot, but these errors are pretty easy to avoid following the simple technique above. I used to transfer from the mini stove pot to a beaker to cool until I realised I was just adding a point of potential contamination. 

As for a difference, I haven't done it side by side, but I have noticed an improvement, and I have stretched single packs further than I should have with no ill results. Nowadays I wouldn't be comfortable pitching dry 1 pack of US-05 onto a 23L wort over like 1.048, and especially not over 1.060. As it is, I rehydrate and even though I'm underpitching sometimes I've had no ill results (1x US-05 for 26L of 1.068 is the highest I've gone before going 2 packs, no starter with dried yeast). Pitching dry in those situations with moderate ester producing strains may be like the straw that breaks the camels back, esp if your yeast pack is 8.5-10g vs 11.5g...

[Ralph]

and then add in the age of the yeast pack... older packs may be less viable too...

[Paul Finney]

Very true Zane.

I had lad in the shop yesterday who is works in a lab and when they use dried bacteria (I think that is what he said, it may have been culture) they rehydrate with water to ease it out of "sleep"

He did also say that in dried yeasts there is a massive concentration of yeast cells so even by killing some by direct pitching it is not the be all end all. But like Ralph says, it would also depend on wort strength and age of the yeast. It sounds even pro brewers have different techniques.

What I am thinking is that if I was to rehydrate I would use just water. By using either wort, or a sugar solution you are almost mimicking direct pitching as you can still shock the yeast with sugar solution which they are not ready for.

[Peter Smith]

from     http://mashtunmusings.blogspot.co.nz/

Wednesday, August 15, 2012

Triple Brewing and How To Go Forth and Multiply

Something we've been doing for quite few years now is triple brewing - not brewing tripel, the Belgian strong blond ale as in Westmalle Tripel or Chimay White - but simply doing three brews consecutively into one fermenting vessel. If one's brewlength (the amount of each brew, i.e., 30 barrels) and FV capacity are the same then there is no need for such extravagant behaviour, however if one has a FV thrice as large as the brewlength, then doing three brews consecutively into said FV will work effectively. The brews can go in three days in a row, which what we do currently with Bigger Bertha (its other name being CT7)  shown below, or straight after each other, without a break, if one is shift brewing around the clock. The first at 8am, the second at 3pm and the third at 10 pm.

Our regular brewlength is 30 bbls (barrels) or in metric speak, 50hl (hectolitres or 100 ltres). We have 4 sizes of FVs - 20, 30, 60 & 120 bbls which means most of our brewing is in 30 bbl aliquots. The two smaller 20 bbl FVs get  brews of 20 bbls and the 30 bbl FVs get the standard 30 bbl brewlengths. But for the two larger FVs (FV8 at 60 bbl and CT7 at 120 bbl, the latter revelling in its status as a dual-purpose vessel - fermenting and conditioning) the dark arts of double and triple brewing must be practised. Those of you with a mathematical bent will be asking yourselves why we don't do quadruple brewing into the largest tank being of four times our standard brewlength of 30 bbls. The answer is we need some freeboard or space above the fermenting wort for the yeast head to rise up. And indeed it does. Especially with the stronger beers. For Blackfriar, our 7% Scotch Ale, for example, we'll brew 3 x 20bbl brews into FV8 and it likes to foam up with serious intent. 

I was reminded of this today by our summer placement student from Heriot-Watt University, Liam, who asked how much yeast we pitch into a double or triple brew. A good question. We pitch 10 litres of yeast slurry to give 18 million cells per ml of wort for the first brew of 30 bbls which is oxygenated for 30 minutes. As the cells take up the nutrients and the oxygen present in the wort, the yeast cells multiply sufficiently to be able to cope with the next brew coming in. This second brew only gets 10 minutes of oxygenation, which allows the now-multiplied yeast to grow even more to be able to ferment the doubled brew in the FV and also, after the third brew is added without any oxygen, to continue the fermentation to completion. A simple tale of yeast going forth into the fermenter and multiplying.

Lia Fail yeast head getting going in style
It's important to get enough yeast cells to ferment out the wort but we don't want too many otherwise the beer will have the wrong flavour, and beer is all about flavour. Having the yeast multiply, generally fourfold during a fermentation, is good for our flavour characteristics, and it's also a lot easier and simple to pitch 15 litres into a brew than 60 litres.
As far as yeast vessels are concerned, we use simple 25 ltr drums into which yeast is run, merely by opening the valve and letting the yeast slurry flow in gently, from the bottom of the cone of an FV of one of the previous week's fermentations.

The drums are stored in a fridge at 3 degrees C where they sit until needed for brewing over the following 6 days. I wouldn't really want to leave the yeast in the fridge longer than a week as it will begin to lose viability and vitality quite rapidly after then. Pitching involves the yeast being pumped into the FV in-line with the oxygenated wort using our yellow peristaltic pump shown below.

This pump from the peristaltic experts, Watson-Marlow, works like a hand milking a cow, gently squeezing the milk down a teat into the milk-bucket, by gently squeezing the yeast through a flexible hose (the clear hose coming out of the right-hand side of the pump) into the fast-flowing wort coming from the heat-exchanger and thus into the FV, getting good mixing with the wort in the process.