Just because they are not fermenting doesn’t mean they’re not doing anything. And what they’re doing, they do faster at 20C than at 4C, which can potentially use up glycogen reserves.
There certainly is such a thing as heat shock, but based on people’s experience here it is not clear if it is relevant when moving yeast from fridge to pitching temps. There are entire classes of proteins that respond to heat and cold shock. Cold shock is relevant when moving warm yeast to lager temps, the response can be induced when moving to 10C (50F).
Tom, using your logic regarding reserve utilization, the minute a starter culture runs low on sugar in the wort, it begins using up its glycogen reserves. I don’t think this is the case. The cells become dormant, their metabolism slows and the utilization of reserves is already minimized even without the further slowing by cold temps. I don’t think viability or health is affected by a few hours at room temp in a beer environment, if it were then we wouldn’t be harvesting viable yeast off the bottoms of fermentors after days of this kind of environment.
Heat shock is a phenomenon that involves subjecting an organism to temps above its normal or optimal environment. Since a yeast’s optimal temp is well above our typical fermentation temp, or even most room temps, I don’t think we are going to find heat shock proteins being expressed in a culture pitched in a properly cooled wort.
Bottom line, yeast is pretty tough stuff and I’m not sure there’s a “best way” here thats head and shoulders above the others.
As the yeast detect the sugar is running low they actually generate more glycogen to build their reserves. Once all of the sugar is gone and their ATP reserves are depleted they have to begin using the glycogen to generate more, there’s really no other choice. Protein synthesis doesn’t stop, even the process of flocculating requires protein synthesis. Living requires energy, and that’s what the glycogen is there for. If you warm the yeast it will begin synthesizing proteins to help it survive in its present environment. If that environment is a warm spent starter then that is what the yeast will protect itself from, including generating ADH2 to begin using the ethanol as a carbon source. That will take energy. Unfortunately, ADH2 only converts ethanol to acetaldehyde (and it is specifically not synthesized in the presence of glucose). What you want when you pitch your yeast into beer is ADH1 to convert acetaldehyde into ethanol, the final step in the relevant fermentation pathway. So when you pitch your re-warmed starter into wort, the yeast have to generate ADH1 and at the same time remove the ADH2. And that is only one example, there are bound to be many more proteins that the yeast need to survive in a an ethanol solution as opposed to wort.
That being said, I’m not saying it is definitely enough to deplete all of their glycogen reserves or even to have more than a marginal affect, especially after just a few hours. But it seems pretty clear to me that from that perspective it is a step in the wrong direction. There may be benefits from pitching warm that offset it, I haven’t tested that either.
As for harvesting after several days, there will be stronger cells and weaker cells and you can pitch a lot to make sure there is sufficient amount of healthy yeast. But that doesn’t mean it’s optimal to keep the yeast under beer.
My point about heat shock was in reference to your comment “if there is such a thing as shock”, because there is such a thing as shock. But I may have misinterpreted what you meant. Anyway, I haven’t read any research for differential expression when moving yeast quickly from cold to warm temperatures relevant to fermentation.
Agreed. I think Denny’s point is that pitching cold works just as well and gives you one less thing to worry about on brew day.
Yeast can survive in beer at a refrigerated temp for some months, lets say two although I’ve kept them longer and still made viable starters. Theres a general biochem rule of thumb that enzyme activity doubles for every 10C increase in temp. Going from 4C to 24C (generous, this time of year its closer to 14C in my basement), we’d see two doublings of activity. Thats a 4x increase in the rate of metabolism of glycogen. So we should at least have two weeks at room temp before our average yeast runs completely out of stored carbs and starves to death. Granted, they’d be darned weak after a week, but all we’re needing is a few hours so I think the fact that metabolism is higher at room temp is insignificant as a practical matter. I’m also not that certain there’s a heck of a lot of protein synthesis going on in a mature, dormant yeast cell. Its kind of the nature of dormancy, that a cell shuts down most synthesis activities and only keeps maintenance metabolism active.
Think we’ve made the OP sorry he asked the question yet?
Can we back up a second to the original question? I am not as experienced as most on here but I definitely understand the thread so far, and I believe the OP is probably a relatively new brewer. Although the details describing crash cooling, etc. that have been discussed are all good, I like the simplicity, and results, of my system. May be a little easier for a newer brewer.
I can’t always brew on a schedule that allows me to make a starter 3-4 days in advance. More often I find myself having a day or so “notice” and can make a starter which I will pitch 12-18 hours after starting it. I based this on MrMalty. No decanting. No crash cooling. Just swirl and pitch. My starter is a few degrees higher than room temp. (Set it on the furnace or in the upstairs bedroom- some warm location). I must note that I only make ales thus far. I make relatively small starters. 750ml. Basically doubling my smack pack count. I am pitching my starter into wort that may be as much as 10F-15F cooler, but that is not an issue as verified earlier in this thread- and also verified by my experiences.
I also brew 2 or 3 batches in a row with the same yeast. In effect, each batch is a starter for the next. I also do this as “simply” as possible. I brew when I know the first batch is ready to be racked- when primary is done. And I pitch the new chilled wort directly on the yeast cake. No washing, etc. I started this as an experiment and I am always willing to improve my practices, but I don’t see any reason to change what I’m doing. And it gives me a great excuse to brew- “but honey, the yeast is calling! I need to brew today!” I know this procedure has improved my beers. And isn’t that what we all strive for- making better beer?!?
You’re probably overpitching on the batches in a row. From MrMalty:
"You might ask why not pitch as much yeast as possible? There is also an upper limit to how much yeast you should add. Logsdon says, “I try to stay within 20% of my ideal pitch rate and I prefer to slightly under pitch rather than over pitch. This causes more cell growth, more esters, and better yeast health. Over pitching causes other problems with beer flavor, such as a lack of esters. Changes in the flavor profile are noticeable when the pitch rates are as little as 20% over the recommended amount.”
Try using the slurry function in the calculator when pitching yeast from a previous batch. Happy brewing.
You are probably right, however I am in the camp of it is better to over than under pitch. Looking at that calculator it says to pitch 65ml of a thick slurry into a 1060 wort. Maybe I am missing something and I should read the entire Yeast book, but 65ml is about half a smack pack?!? How is that enough yeast? Even with a much more concentrated amount of cells in a slurry, that volume just doesn’t seem right. But, I haven’t tried it and eveything else I have tried from MrMalty has worked so…
I like the feeling that the “pitching on a cake” procedure is rather simple. Taking the time to actually measure the volume of slurry is an additional step that seems unnecessary when what I have done so far is working well. My last 3 step “batch” was a Dark Mild, Brown Porter and finally an EBW, all with NeoBrittania. Damn fine Mild, porter is bottle conditioning now, EBW just finishing primary. All I know is the blow off from the EBW was HUGE. It went from 1.104 to 1.046 in 3 DAYS. And is at 1.032 after a month. That attenuation rate is right in line with the first 2 batches. Not exactly in line with what the strain guidelines say, but it consistent with the numbers in my system. Only time will tell. 2012 Nationals?!?
I probably could pitch 2 or 3- 5 gallon batches with the yeast from the EBW… mmmm… that would be this weekend…
Enzyme activity is not important here, whether protein X is more active when 10C warmer doesn’t matter. Below 10C most yeast strains are shutting down and preparing to be frozen, I think you’re right when you say that “I’m also not that certain there’s a heck of a lot of protein synthesis going on in a mature, dormant yeast cell.” They will create cryoprotectants like trehalose and upregulate various proteins so that they can freeze solid and have a decent chance of survival. They have evolved that way because if you don’t start protecting yourself when it gets cold, then when it freezes you die. So the things they are generating are different and they will eventually shut down as much as possible. This is not the case at 20C, there they will be trying to grow and survive, using whatever carbon source they can find on hand, and in a beer ethanol is plentiful.
Obviously the yeast can survive much longer than a few weeks, I’ve cultured from bottles that are much older and shipped from Europe. But I take what grows and baby it for a while and grow up a healthy population before I ask it to make me any beer.
I have yeast that is more than 4 years old, and it was more then 3 years old last time I checked it. While he was working on the new book JZ asked me to update him on some stuff I did for NHC in Denver. The yeast sitting at room temp (garage temp with large temperature fluctuations over the course of a year) were pretty messed up, but they were alive. Every cell that grew formed a petite colony, indicative of a loss of mitochondrial function, which also means a loss of respiration ability. The cells that I have at 4C and -20C came out much better - not as good as the -80C controls, but alive and functioning. I didn’t do any fermentation tests to see how they perform.
So anyway, I’m not convinced that warming them up will make a huge difference, but if temperature shock isn’t an issue then there doesn’t seem to be any upside to it . . . unless you are adding something to get it going, like happens in a wyeast smack pack, then that changes the equation.
You’re right that it’s all about the concentration of the cells. If you assume that a 125ml smack pack has 100B cells at 100% viability that’s a concentration of 0.8B cells/ml. Depending on the thickness of the slurry Jamil’s calculator is assuming 1-4.5B cells/ml. If you assume on the upper end of that range you’re going to need a lot less volume of slurry to get the right pitching rate.
I think the challenge is determining what concentration you want to use as an estimate. How thick is your slurry, how much non-yeast crud do you have in there along with the yeast? Unless you’re counting cells with a microscope it’s got to be a pretty wide margin of error. Which is going to be close enough for most of our purposes.
Right theres not 65ml of SLURRY in a yeast vial/smack pack.
On the subject of trub as a percentage of east cake, I was in the habit of pitching most all my trub into the fermentor, just running the wort through a mesh screen to get rid of larger pieces of hops. I’d get a nice healthy inch of yeast cake. Recently I’ve begun colling and racking my wort off the trub prior to pitching, and I’m get about 1/3 as much in the bottom of the fermentor. Its much lighter colored and finer. Bottom line, I bet the slulrry volume recommendation is based on having the trub removed first so you’d be quite low on cell count if you don’t remove trub via whirlpooling or some other means.
On the trub topic, I use DME to make starter wort and even with a short boil I get a pretty substantial amount of hot/cold break. This is the stuff that drops quickly, so even if you are relying on visual volumes in these things you might be over-estimating.
Finally, if you pitch a vial in 750ml of wort will it even double once? There was a discussion in Yeast about this, you might not get much of an increse in cell count with this method but it would at least get the yeast active and give hem a running start. I think there’s something to be said for a “running start”, in the few times I’ve done it this way I see activity sooner. Looks to me like there are cellular activities that take some bit of time to ramp up before even cell membrane component synthesis can begin. You have to make some enzymes and express the right proteins before you can make triglycerides and cell membrane proteins.
That’s a good observation. I’ve heard Jamil say on a few Brew Strong episodes that he always washes his slurry so you’re probably right that’s he’s factoring out a good amount of trub in his calculations. Although if you use a lower cell concentration without washing I think you could get pretty close.
Your slurry, free of a lot of the trub is probably closer to the higher end of the spectrum at 4B or so cells per ml whereas mine, with the trub in, would be on the lower end of the range.
I do agree with this statement and don’t think either that there will be any appreciable yeast growth, especially if the yeast is starved. When you add yeast to this wort all living yeast cells will start consuming the nutrients at the same time. When the nutrients are then consumed hardly any of the yeast cells will have been able to take up enough nutrients to grow a daughter cell.
But as tom said, the nutrients taken up by the yeast are not lost. The yeast cells are stronger and healthier than before and even though they didn’t grow in the starter they’ll start budding in your beer earlier than they would have without the starter. In a sense you didn’t grow the number of yeast with this starter, you only grew the yeast cells themselves and brought them closer to your first bud.
So on Saturday I pitched a cold pint of thick slurry that was stored in the fridge for ~24 hours. It worked just fine. Noticeable fermentation within 4 hours & in full stride @ ~18 hours. Just thought I’d share that. Cheers!!!
Tom and Tom touch on an interesting topic that I have been thinking about as well: How to best preserve the yeast health while the yeast is dormant. I have noticed that there is a noticeable difference in the fermentation performance that I get from yeast that sat 1-2 days in the fridge after propagation vs. yeast that sat in the fridge for 4-5 days. I try to avoid letting the yeast sit dormant for too long but sometimes life gets in the way.
I generally do take the yeast out of the fridge, decant and re-suspend the yeast with 15-20 C wort. This is the temp the wort is at after I places the kettle in an ice bath to settle trub and chill it to 4-6 C for about an hour. Re-suspending the yeast allows me to count it but more importantly allows me to disperse it evenly throughout the wort. It bothers me that I have to do this in slightly warmer wort but chilling that wort would mean more effort. The whole thing is then pitched into the 4-6 C wort which may shock the yeast but I haven’t seen lag time issues. In the past I found lag time to be mostly a function of the yeast amount, yeast health and wort temperature.
While the yeast will start consuming its reserves faster when warmed up I doubt a few hours will make a difference although I do concur that a simple remedy is to take the yeast out of the fridge later.
Another thing I heard is that we should avoid the introduction of O2 when harvesting yeast. That additional O2 may trigger a rise in yeast metabolism. While I do think that there is some merit to it I cannot see myself go through the effort of purging a carboy with CO2 before swirling up a yeast cake for harvest.
Let me comment on this since I must have missed this initially.
There is nothing wrong with this. In fact you should make the starter part of your recipe. If your are an extract or partial mash brewer it is very easy to do.
Simply take some of the water you’ll use for the recipe and some of the malt extract ad make a 2-4 qt 1040 - 1050 starter the day before. Treat this like you would be treating the beer: aerate well and pitch the yeast at or below fermentation temps. Then brew your beer with the remaining ingredients, chill, aerate and reunite all the ingredients by adding the “starter” which is likely at high Kraeusen by now.
This way you should be able to pitch from a single vial and have a proper pitching rate for your beer.
