I experience heat being generated during the lag phase – it seems to be at least as much as during active fermentation. But I’ve never found any published information to substantiate that. Does anyone know if I’m crazy, or it that is an actual phenomenon. (Note: the two aren’t necessarily mutually exclusive.)
I use a TILT floating hydrometer that logs temp and gravity. I usually see a degree to two (°F) rise in temp before I see a reduction in gravity.
For example, this is a data excerpt from Harvest yeast pitched in a Session Strength Dunkel. I pitched ~11:30 (before I started the log function), saw a temp increase at 5:30, and a gravity decrease at 9:40:
8/16/2023 22:40:43 1.037 58.0
8/16/2023 21:40:43 1.037 57.0
8/16/2023 20:00:51 1.038 57.0
8/16/2023 19:00:50 1.038 57.0
8/16/2023 17:33:12 1.038 57.0
8/16/2023 16:27:16 1.038 56.0
8/16/2023 15:12:56 1.038 56.0
8/16/2023 14:12:55 1.038 56.0
8/16/2023 12:52:45 1.038 56.0
I always use the first gravity point drop logged as my fermentation start point. So, I would say this yeast started in ~10 hours. …but I could probably say it started in ~6 hours because of that temp increase.
BTW, I am thoroughly impressed with Imperial yeast straight from the company. I received two pitches as a result of a beer contest I placed in. I chose Dieter and Harvest. Both started fast and finished strong. Dieter produced clear Kölsch faster than any other Kölsch yeast I’ve ever used and it tastes great. I anticipate great results from this Dunkel as well.
Maybe you’re misinterpreting things. There is no distinct lag phase. Fermentation begins immediately.
I believe the common homebrewer would say the ‘lag’ in the above example would be 6-10 + hours depending on their definition of start: temp increase, gravity drop, or bubbles in an airlock (which I don’t monitor).
I have a homebuilt Tilt-style hydrometer and a PID loop that controls the temperature of a liquid bath in which the beer sits. I log both temperature and the power required to hold that temperature. The power rises as fermentation produces heat. I often see a slight drop in SG before there is any noticeable heat production and before there are any bubbles visible. Then the power starts to creep up at about the same time that bubbles first start to form At that time the hydrometer reads an increase in SG as the bubbles get trapped around its edges. After a while the hydrometer reading begins to drop as full krausen forms and bubbles are everywhere. The power continues to rise steadily until it reaches a max at the peak of fermentation activity. Then the power drops steadily until it reaches a base level required to compensate for heat leakage into the system, which has a distinct diurnal component. Here is a link to a document with a graph showing all this:
That’s very cool.
BrewBama: Your data seems to agree with my perception.
Richard: Your data doesn’t seem to support my perception.
Denny: The more I study brewing, the less I know.
I should note that my observations are crude. I use a simple swamp cooler and add ice bottles when needed, so my feeling for heat generated is based on how often I need to add ice bottles. With ales, I usually pitch 2 – 4 degrees F below my target active fermentation temp, so around 65F give or take. I seem to get much more heat generated if I pitch at 68F.
Read about the Crabtree effect. Basically it says that in the presence of >.5 % glucose, fermentation begins immediately
While there is no doubt ‘the phenomenon whereby Saccharomyces cerevisiae produces ethanol in aerobic conditions at high external glucose concentrations rather than producing biomass via the tricarboxylic acid (TCA) cycle’ (aka the Crabtree effect) is a thing, outside a lab equipped with a chemostat it cannot be easily observed by the avg homebrewer.
What is easily observed by the avg homebrewer is a rise in krausen, airlock activity, a slight temp increase, and a drop in gravity. These signs of activity take time. That time is routinely termed “lag” even though there may be no “lag phase” in Saccharomyces cerevisiae life cycle.
Brewing Scientists…
The things that BrewBama points out as easily observable by a homebrewer are only observable when they happen on a large enough scale. They may be happening on a much smaller, unobservable, scale during the “lag” phase. It takes time for the yeast population to grow and for the activity to rise to the easily observable level. The CO2 production, gravity drop and generation of heat are all linked to the fermentation and I don’t see how you could have high heat generation without the other observable consequences. Small heat production maybe, but not as much as at the peak of fermentation as the original post stated. Perhaps the whole mass of the swamp cooler system is being cooled down during this time and it requires more ice but not because of anything happening in the beer.
I agree – I don’t see why there should be significant heat production during what we (maybe incorrectly) term the “lag” phase. But my crude observations tell me it does. If it didn’t defy the laws of physics, I would feel sure it was happening. But given those pesky laws of physics, I think I’m mistaken. Well, that’s why I asked. I got some answers, along with a refresher in Crabtree effect. Really, it’s mostly curiosity - I’ll control temperature either way.
I need to do some more reading to re-familiarize myself with the exact workings of the Crabtree Effect. Unless I am way off base here, during the growth phase (maybe incorrectly called the “lag phase”) my recollection from reading previous articles on the fermentation process is that during this phase which is aerobic, the yeast cells take up oxygen in the wort and build cell walls and biomass. Then the yeast changes to the the anaerobic phase where it ferments glucose, maltose, etc. to produce alcohol. If the yeast is over-pitched, then fermentation begins much faster because the growth phase is reduced (Crabtree Effect)
Correct me if I am interpreting this incorrectly.
From the More Beer website, referencing the Siebel Institute (though I can’t vouch for its veracity):
“Yeast growth can be divided into five stages.
Lag phase occurs during the first few hours after inoculation. Although no signs of fermentation or growth are apparent, the yeast are busy becoming acclimated to their new environment. All the enzymes and other metabolic machinery necessary to ferment wort into beer are being synthesized. All the oxygen you introduced into the cooled wort is taken up by the yeast within the first 20 min and is being stored (as sterols and unsaturated fatty acids) for later use.
During the accelerating growth phase, yeast cells start to divide rapidly.
The actual number of yeast cells increases during the logarithmic phase. During this time the number of yeast cells may increase as much as 1000-fold (or 3.0 logs) within 24 h.
As the oxygen and nutrients are depleted, the yeast enter a phase of decelerating growth (approximately 12 h) and ultimately reach a stationary phase.
During the stationary phase, yeast growth ceases.
Despite the rapid rate of yeast growth, a relatively large yeast starter or slurry of yeast is required for optimal beer production. Siebel Institute recommends one-sixth of the batch-size, one-tenth if you continuously aerate or agitate your starter. The scientific basis for this is currently unknown.”
A friend (pro brewer) who attended and is Siebel credentialed used to always reference the lag and log phase as simply the preparation (for growth) and the growth phases…FWIW.
I think we can all be correct.
Like Richard says:
This unobservable activity is simply what we’ve dubbed the ‘lag’. If we had instrumentation that could observe the micro-activity we may conclude that Denny is correct:
All I can go by is the numerous TILT data logs I have collected that show a time gap between when I pitch the yeast and 1) a slight increase in temp, then some time latter 2) a decrease in gravity. I always see them in that order. I am not suggesting the TILT is a piece of laboratory accurate equipment. It’s simply what I have to monitor fermentation.
The relative sensitivities of the Tilt’s thermometer and hydrometer could be another explanation for why you’re seeing a measured change in one earlier the other. It would be interesting to see the plot of the change of both variables with respect to time using highly sensitive devices.
I agree that what we are seeing as a lag is likely due to the sensitivity of our equipment, and the end of this phase is likely arbitrary based in how we choose to measure it. I suspect that “rampup phase” is probably a more accurate description than “lag phase”
Because of the Crabtree effect, the yeast will always be in an anaerobic state, even in the presence of oxygen. In an aerobic state, the yeast will produce very little alcohol or co2. Most of the carbon (sugar) will be used to create biomass. As brewers, we want yeast in an anaerobic state to produce alcohol and co2
The oxygen needed during a “lag” phase is used by the yeast to produce lipids for cell wall production. It’s nearly impossible to get the yeast in aerobic state during beer brewing. The gravity of the wort must be below 1.012 or so and have constant aeration to achieve aerobic respiration. This is the method used by dry yeast manufacturers to produce yeast. Yeast manufacturers also “feed” the yeast to keep in this state which produces maximum biomass from the available carbon.
For all practical purposes, there is a lag phase. To argue otherwise is the pointless splitting of hairs.