Dry yeast and pitching temp

I've seen odd guidelines.

Like pitch at ferm temps (kinda makes sense, but feel that rule of thumb is for liquid yeast)

For dry yeast the packets almost always (at least the tones I've used) say to rehydrate at around 90F.

So if the 90F doesn't kill them, why can't I pitch at less then but close to 90F? What would be the reason to drive the wort temp down to ~65F before pitching?

(I gotta say that I've pitched into a ~80F wort and the fermentation was more then stellar; maybe too quick, which could be an issue)

Talking ales (but can't see why Lagers would differ much if the packet says rehydrate @ 90F)

We're not talking about fermenting when you're rehydrating dry yeast. Rehydrating just allows water to absorb into the yeast and let them become active again.

I've pitched into hot wort plenty of times and never had an issue, but it will create off flavors since the yeast are being overworked. I highly doubt you will "shock" your yeast by pitching them into 85-90F wort unless it's a delicate yeast or lager yeast.

Also, when you're rehydrating, the yeast aren't eating anything. When you pitch the yeast, the high temperature of the slurry is offset by the large amount in the fermentor and the yeast are then brought to a normal temp where they're comfortable feeding.

On a side note... rehydrating isn't really necissary in my opinion. I've pitched without rehydrating a few times, and I've never seen any bad side effects because of it.

If you pitch when the wort is warmer, you many not get down to fermentation temp before the yeast takes off. Especially since everything the yeast do (like reproduce during the lag time) happen faster at warmer temps. So if you want to ferment at 65, but pitch at 90, the wort might only get down to 80 when the yeast start fermenting, vigorously, and they start generating their own heat making it even harder to cool the beer down to 65.

ChshreCat said:

If you pitch when the wort is warmer, you many not get down to fermentation temp before the yeast takes off. Especially since everything the yeast do (like reproduce during the lag time) happen faster at warmer temps. So if you want to ferment at 65, but pitch at 90, the wort might only get down to 80 when the yeast start fermenting, vigorously, and they start generating their own heat making it even harder to cool the beer down to 65.

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Not only harder to cool down, but it'll kick off tons of esters that should not be there. You really do want to pitch at appropriate temperatures.

If I pitch at 74-75 ish and my ambient fermentation temp is 69, do you see any problem with that? I know the wort temp increases a few degrees when things get kicking. That's about the best I can do in the summer time here in Delaware. I am using Nottingham yeast...

Last Thursday I pitched Nottingham at 75 degrees, it started fermenting 30 hours later, it stayed at 75 until is was done fermenting on Sunday night, then dropped to 70 by Monday morning.

I measured gravity today and tasted the sample, there is a little astringent in there, but I think that it will clean itself up if I primary for two weeks, then secondary for two weeks.

Anytime you pitch above your fermentation temp, you're giving yourself an uphill battle.

But the fridge just stays on until the wort is cooled to fermentation temperatures, which usually happens before any visible signs of fermentation.

Yeah, but I'd still try to pitch at fermentation temps. If you get a quick start, it might still be warmer and most of the bad flavors that a warm ferment can throw off happen right at the start of fermentation. Even if it's just a couple hours, it can have an effect. Not saying it's going to happen to you, but I like to try to give my beer every chance it can to come out like I want it to.

ksbrain said:

But the fridge just stays on until the wort is cooled to fermentation temperatures, which usually happens before any visible signs of fermentation.

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When you see visible signs of fermentation, the yeast have already done most of their initial reproducing and have started eating.
According to literature that I have read on the internet (http://brewiki.org/BeerFlavours#head-ca729d7916193306af853d5b853be848cfe258a1), ester production is less during the initial reproduction stage if your wort temperature is higher due to the fact that both yeast growth and ester production need the Co-enzyme-A. During the initial reproduction stage, Co-enzyme-A is busy and therefore not available for ester production.
Higher temperatures after the initial reproduction stage promotes higher ester formation, so if you manage to cool the wort down before the yeast have reproduced, you may be in the clear for the ester part.

There are other factors that piching and fermentation temperatures affect, one of which is the diacetyl production.
Higher pitching temperatures promotes diacetyl production, and it may be so excessive that the yeast will not be able to clean it up sufficiently in the end of fermentation. You may end up getting some butterscotch smell/taste in your beer.

The exothermic effect that fermentation has, may provide you an uphill struggle when trying to cool down so you may end up getting more ester flavor compounds than desired if you are not able to control the fermentation temperature.
See http://www.howtobrew.com/section1/chapter8-1-3.html

So, pitching higher temperatures and allowing the beer to cool before any visible signs of fermentation may give you less esters, but you promote the diacetyl production excessively. Exothermic reaction may provide an uphill struggle if you are not successful in controlling the temperature of your fermenting beer, resulting in increased ester formation.

That being said, I suggest that you try both ways and see what result you are happy with.

I always pitch five degrees *under* fermentation temperatures, especially in the summer. The reason is because it takes my refrigerator (which is in the garage) a while to stabilize with the wort temp. I want the wort to cool down the fridge, not the fridge to cool down the wort. It takes a long time for ambient air that is only 5-10 degrees cooler to cool down 5 gallons of liquid. During that time, I don't want my wort in the 'danger zone' for esters.

My fridge in my basement seems to do a pretty good job cooling the wort down those last 10-15 degrees in just a few hours. I my next best option would be to wait those few hours then pitch the yeast, but I know that for me that would be a recipe for forgetting to pitch the yeast. Interesting information.

Bumping an old thread rather than creating a new one.

Brewing an IPA using US-05 and I'm hoping to keep the fermentation temperature in the low 60s. Should I cool the wort and dry pitch the yeast into the 60ish degree wort? Or should I pitch at room temperature and place the fermenter in the chamber and let it cool then?

Wasn't going to rehydrate but should I? And if so how does that affect my plan?

You could do either one. Just may see a longer lag starting in low 60's. I pitch a dry pack 70-75 and then cool down to 67 most times. I don't rehydrate US-05 and it's always taken off.