24 replies to this topic

[Salsgebom]

This is a good discussion here. I appreciate the insight and knowledge the people on this board are willing to share.

The homebrew forums are fun because it motivates me to re-read my notes. Sometimes the best way to learn is to teach.

What's often overlooked by stir plate crazy brewers, is that having low sugar levels is even more critical than keeping o2 levels high. Even with o2 present, high glucose concentrations will inhibit the yeasts ability to respire. This is called the Crabtree Effect.

edit: Important bit of information that I missed- high glucose levels don't just inhibit respiration, it forces the yeast into anaerobic fermentation phase. THATS the Crabtree Effect.

[Salsgebom]

And any sugars above 1.040 will just make alcohol, no matter how much you aerate it.

Why's that? If true, that would imply that we wouldn't be able to increase cell count in a batch of beer since they're all above 1.040, and that we've been wasting our time oxygenating full batches.

I'm also hazy on this. This topic is worth contacting my instructors (oh yeah now I can make Chuck D do that for me )From comparing my notes on propagation vs. fermentation, it seems that nothing is cut and dry. Based on some graphs in front of me- oxygen pickup, yeast growth, alcohol production, etc don't necessarily start and stop as the yeast change phases. They just peak when their respective environment is optimum, and decrease otherwise.

[Stout_fan]

Why's that? ...

It's called the Crabtree effect

...that would imply that we wouldn't be able to increase cell count in a batch of beer since they're all above 1.040, and that we've been wasting our time oxygenating full batches.

Interesting point. I'm sure some O2 stays in solution for when the gravity drops below 1.040.Remember a 1.055 wort drops rather quickly at first. Getting down to 1.040 wouldn't take long.Some folks oxygenate later in fermentation. However, that comes with a risk of oxidized beer.

[Stout_fan]

I see Salsgebom beat me to the answer.Like alpha and beta amalyase, they all don't stop and start EXACTLY at said temp. OR in this case SG.It's not 1.03999999999999999999999999999999OK, I can bud.1.04000000000000000000000000000Stop budding!There are variants on each yeast strain and multiple mutation in that.I like watching my meads drop clear.In a 5 gallon carboy, there are generally 5 or 6 distinctly different bands of clearing viewable at one time.This is each mutated yeast strain's ability to ferment alcohol point of giving up.Same here, some will have a bit more capability. Starters over 1.040 are a waste of DME though.My starter is Ideally 15 point something ounces of DME.I remember a pound. It's a lot easier.One tsp of Superfood. And fill with filtered water to the 4000 ml mark.5 drops of foam control And throw in the stir bar.Plunk on the stirplate to get all in solution (no scorching of the DME that way).Al foil cap and on the stove till boil.Just before boil, one Tbsp of bakers yeast. I buy a 500 gm brick over at Costco.

[zymot]

It's called the Crabtree effect

Crabtree effect is when a yeast has an inflated opinion of itself. It cannot face the fact that 9 yeasts were chosen ahead of them. For some ill-conceived idea, they do not like the 1.049 wort they were selected to work with. Then threaten to sit out the entire brewing session and re-enter into next year's draft beer.For more information, brewbasser can provide us details.