using air for agitation of Mash

[bpsisk]

Hello everyone,

I was wondering if anyone uses air bubblers for slight agitation of mash while its fermenting? any positives or negatives for this type of practice?

[MtnMann]

You don't want to be adding O2 to your mash after it's started to ferment. How about using a little pump to circulate?

mtn

[Artisan Still Design]

anerobic fermentation makes alcohol, in an aerobic environment yeast multiplies, no alcohol produced.

plus you increase your chance of introducing an infection.

[bpsisk]

I thought adding air was a bad idea, do you even think a pump is necessary? i was reading somewhere how agitation helped the fermentation process, so i was just trying to find a low budget answer to this question, even though ive never had any issue without agitation. Probably just a dumb question, but I am a tinkerer by nature.

[MtnMann]

Fermentations that I have done seem to agitate themselves.

[daveflintstone]

I've been agitating people for years but I don't bother the fermentation.

[Shindig]

I have heard that adding air to rum fermentation is a GOOD thing for the first 24 hrs or so….

[Artisan Still Design]

I have heard that adding air to rum fermentation is a GOOD thing for the first 24 hrs or so….

maybe not 24 hours, but in the first part of the ferment, in order to promote yeast growth.

if you took a molasses ferment and added a oxygen injection at a low constant rate, you would end up with an exceptionaly good yeast bloom, with very little alcohol. this is how yeast is propagated (perhaps much simplified) for breweries, bread and whiskey ferments.

[stevea]

anerobic fermentation makes alcohol, in an aerobic environment yeast multiplies, no alcohol produced.

plus you increase your chance of introducing an infection.

True enough wrt pure anaerobic fermentation (the glycolytic pathway) vs aerobic fermentation metabolism ( respiration using EMP & Krebs cycle) *BUT* this won't happen in your fermenter. S.cerevisae yeasts and a lot of other fermenters exhibit the 'Crabtree effect'.

Crabtree effect literally means that these yeasts cannot respire when the gravity of a glucose solution is above 0.4 Plato (~1.0016SG) no matter how much oxygen is present, however this same mechanism also prevents yeasts from respiring in slightly higher concentrations of any other reducing sugar. Yeast respiration is not possible when the sugar concentration is significant.

This is believe to be a competitive advantage issue wrt yeasts and other spoilage organisms. The yeast strategy is apparently to use all the oxygen in solution in a matter of minutes, then they drop the pH sufficiently to stopa lot of other organisms, then finally they convert the sugars to ethanol which only obtains about 15% of the energy in the carbs, but ethanol is inaccessible to most competitors.

What many brewers & distillers do not know is that yeast are capable of converting ethanol into CO2 an completing the respiratory cycle, but this requires oxygen. I've read that (in some of the Scottish distiller lit) that there is a measurable amount of ethanol loss to CO2 when open fermenters are kept a couple days too long - several percent loss.

I have heard that adding air to rum fermentation is a GOOD thing for the first 24 hrs or so….

Yes, it can be extremely important. Yeast membranes require sterols and unsaturated fatty acids for good performance; but to make each of these requires oxygen. As yeast ferment anaerobically in a closed fermenter then can go for 3 or 4 generations without any additional oxygen as the sterols & UFAs are split between the sister-cells as the yeast divides. When the sterol level gets low enough, the cells cease to divide further, and as a result their metabolism and the rate of fermentation slows dramatically and flocculation occurs (stuck fermentation). Low sterol membranes are more porous, so the cell has to expend more energy keeping ion levels balanced and removing ethanol and esters. More bad-flavored yeast by-products are produced when sterols are low.

I'lt note that commercial dried yeasts are produced in a way so they have high levels of sterols and a modest oxygenation is sufficient. Anyone using a starter, esp one that has flocculated needs to oxygenate well. Also that high sterol levels are a primary reason why some yeasts are more alcohol tolerant (really a misnomer). Also note that the oil'ier grains (corn, maybe oats, but not rye, wheat, barley) exude a lot of UFAs that the yeast can adsorb.

I've read papers (google/scholar Chris Boulton, David Quain) that show 24 hours of oxygenation in a brewery context of ~6 or 7 day fermentation has a positive impact of alcohol production an completion rate *BUT* the there are potential negative aspects on flavor wrt fusel production with later oxygenation. I think I'd personally restrict oxygenation to the first 12 hours or so, but I won't throw stones at the 24hr idea - it's not far off of optimal. What is clear is that yeast need more oxygen for rapid/clean fermentation. Also b/c there is a storage carbo prerequisite for sterol production (trehalose) the oxygen can only be use to produce sterol in the early phase after pitching a dormant yeast, or else after a substantial delay (days) when you really wouldn't want to oxygenate..

maybe not 24 hours, but in the first part of the ferment, in order to promote yeast growth.

if you took a molasses ferment and added a oxygen injection at a low constant rate, you would end up with an exceptionaly good yeast bloom, with very little alcohol. this is how yeast is propagated (perhaps much simplified) for breweries, bread and whiskey ferments.

Again right ... but you are missing critical facts. In commercial yeast propagation they use massive amount of oxygen. For complete aerobic fermentation you need ~ half as much oxygen mass in solution as sugar, so a 30P wort needs a POUND of oxygen per gallon !!! (it's hard to keep 50ppm in solution at any one time). Also these yeasts exhibit the Crabtree effect, so they don't really use what we think of as molasses. They use thin cane sugar waste and they slowly add this thin sugary solution to the propagation unit while keeping the amount of sugars below the 0.4P limit. It's incremental feeding.

[Roger]

We plan on using a twice daily gentle pump over inside our closed fermenters. Has anybody done this vs agitation with a mixer ?

[mendodistilling]

You want to oxygenate wine in a different way, you break the cap and release sulfur compounds, so it depends on what you are making, like with grain fermentation, rum, wine, all the fermentables, the yeast needs to build cell walls using lipids and oxygen to make a permeable membrane, so this is the first stage of log growth. After log growth, anerobic fermentation needs to be happening or you will end up with acetic bacteria and other things that grow in aerobic environments taking over, as well as, creating vinegar, which is also nice when you do it on purpose. However, your either going to get vinegar or beer/wine depending on your initial level of 8PPM oxygen target applied at the beginning and not anytime after. Sometimes you have to push down caps of wines, etc, this is more for releasing volitile compounds than for aeration as well as to use skins moistened and used for color extract, not usually a target with distillation because of tannins. Usually you take the white wine approach and seperate from the skin right away by pressing off. Then you want to keep it from being oxydized, so basically when distilling, oxygen only 8PPM for the beginning, its bad after that.

[mendodistilling]

On another note, when people pump over product back onto itself, there is generally plenty of co2 in the tank to dispace the oxygen off the surface of the wine. So the wine stays free of or has limited oxidation. if you are worried about sulfur compounds with on grain fermentation, this could be an option. The company that makes the racketeer makes a tank sprayer that sprays and recirculates the liquid inside red wine fermenters to keep the cap moistened and allow sulfur to volitize. I think temperature is a big factor here too because of the 80+ or mainly 86-95 degree range when sulfur will be produced heavily if not handled correctly.

They also make lightning pumps that mount at the bottom of tanks to create movement but that could aerate too.

[mendodistilling]

Rereading your post, there will likely be more than slight agitation of the mash from CO2 produced as long as its above 68 degrees.

[Roger]

Sorry, I didn't make it exactly clear. We fully intent to maintain the CO2 cap, by keeping the system sealed. The "pump over" is merely the process of agitation with a pump, vs a mixer. The idea is to be able to move one pump on a cart down the line between fermenters, a couple of times each day, vs putting a fixed agitator on each fermenter.

[mendodistilling]

Yes, that is quite common, in the wine industry it is done 4x a day, about every 3-6 hours. Definitely cheaper than a guth lightning pump on each fermenter. In the beer industry though, natural currents form inside the fermenter from up currents on the outside then circulating back down the middle. There is a natural mixing going on and the cap ddoesn't get hard like with fruit skins. It causes a little Krausen but not much.

[Roger]

Sweet. Thanks !

[Natrat]

Interesting thread...

I might point out that overoxygenation at the start of fermentation is a significant contributor to producing what we call "pre-staling" compounds in beer wort. I'm not sure if it's significant for distillation, but I have my best whisky results with a regimen that is very similar to producing beer wort.

I would limit oxygenation or aeration of your wash pre-ferment to just a few hours at best. Another alternative, if you are using liquid yeasts, is to add oleic acid to your stressed, chilled yeasts in storage. The yeast takes up the oleic acid easily, and it helps to strengthen the cell walls prior to being pitched into a sugary liquid with high osmotic pressure. This allows your yeast to survive the early stages of the ferment, which in turn helps out-compete other infections. It's true that this method means that the usual rapid reproduction phase of yeast at the beginning of the fermentation is delayed (I've seen lags of 6-36 hours, depending on the size of the pitch and the gravity of the wort) but the resulting fermentation is relatively rapid and produces a measurably large ester profile. I've noticed lower krausening as well. While olive oil is a well known source of oleic acid, I would recommend grapeseed oil, as it seems to always be clean when I plate it. Olive oil is sometimes clean, but often comes up TMTC. Rates are really really low. Generally, I'll add 2 ml to a 5 gallon pitch...even less would be ok...like one drop.

If you are using pure oxygen into your wash, consider the cost savings of a single bottle of grapeseed oil over a decade, rather than a tank of O2 every week. The downside is the lag...if you are in a production environment that demands your wash ferment out in, say, 27 hours...or 40 hours...an additional lag of 16 hours may be unacceptable. But for us smaller types, no problem.

I've not tried this with wines, but it seems like a good way to limit the growth of aerobic infections that might be competing with your primary yeast strain. I'll also point out that it will strengthen any wild yeast you have in your liquid pitch, but limit their reproduction if they are in the must, and not the pitched yeast.

Fun stuff!