From experience, I agree with the previous respondents that all the potential problems are easily manageable. You should not run into too much trouble. Wort depth is unlikely to cause significant hydrostatic pressure problems.
From experience, some factors to consider are:
1) Height to diameter ratio should be between 2-3:1 to achieve proper mixing and efficient cooling (if you are using cooling jackets).
2) Headspace (expressed as % of total vessel volume) should be at least 20%, to prevent fobbing losses and subsequent quality issues.
3) Cone angle should be 60-80 degrees to ensure optimal yeast sedimentation (especially if you intend to re-pitch the yeast to subsequent batches).
4) Hygiene: As you mentioned, CIP should be easier (and more effective). I recommend that you invest in suitable sampling valves, to ensure sterile sampling and effective valve cleaning (e.g. Keofitt).
5) Think "outside" the fermenter. I have seen perfectly designed FV's compromised by poorly sized vent and/or CO2 collection piping. Back pressure should be as low as possible and certainly below 30 Kpa.
6) Not sure if you wish to use combined fermentation and maturation tanks or keep them separate? Perhaps that is the topic for a future discussion.
7) You asked for some literature references. Here is a selection which I hope you will find useful. Some of the work focuses on very large fermenters but, hopefully your business will grow:
Fermentation Systems (2001), Boulton, C., Quain, D.E., Brewing Yeast and Fermentation, Blackwell Science, pp 260-376
The Impact of Sedimentation on Cone Yeast Heterogeneity (2004), Powell, C.D., Quain, D.E., Smart, K.A., J. Am. Soc. Brew. Chem., 62(1), pp 8-17
Thermal Convection in Cylindro-conical Tanks During the Early Cooling Process (2003), Takamoto, Y., Saito, Y., J. Inst. Brew., 109(1), pp 80-83
Stirring Stuff (2009), Boulton, C., Brewer & Distiller International, June 2009, pp 18-21
Stratified Fermentations - Causes And Corrective Actions (2008), Kapral, D., MBAA TQ, 45(2), pp 115-120
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Christopher Williams
Owner, Hoppy Bulldog (Serving Hong Kong Beer)
Hong Kong, China.
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Original Message:
Sent: 05-14-2024 15:14
From: Travis Audet
Subject: Fermenter Geometry: pros & cons of tall/skinny tanks compared to
In regards to the skinny tank discussion I would start with the Ask the Brewmasters Podcast I did on tank temperature stratification and the paper I referenced by Jim Larson et al. In that podcast, I only talked about temperature stratification issues and did not even touch on esters and CO2 and cell health.
https://www.masterbrewerspodcast.com/296
Here are some "cliff notes" on those other topics:
Define what pressure:
A lot of quick "facts" get thrown around in brewing about pressure without even defining what kind. Osmotic pressure from high gravity and very high gravity wort is very different "pressure" mechanism than hydrostatic pressure and we should always call out which one we are talking about before making generalizations. I know we are discussing hydrostatic today but there seems to be confusion when generalities are made.
Esters:
esters are a function of yeast strain chosen and then degree of yeast grown. The more yeast growth (all other variables the same) then less esters. In very tall tanks there have been claims of reduced esters due to CO2 inhibition. As tanks get really tall (say 60ft!) the amount of CO2 that is in solution can rise. This is more of an issue for colder lager fermentations as the CO2 solubility is higher. In my experience higher hydrostatic pressures (or top pressure) often does lead to lower ester formation in yeasts I have worked with. However, I have never connected this to cell health issues. Whatever the exact mechanism is for lower esters in tall tanks, the yeast we ferment with and collect for re-pitching can be very healthy with good brewing practices. When moving fermentation to tall tanks our teams have had to make some adjustments for a perceived differences but nothing that cannot be overcome (unlike the challenge of CO2 inhibition). If CO2 inhibition does occur, the brewer would hopefully be able to make other changes to return yeast growth and ester profile back to the desired level. For the volumes you are discussing I can't imagine CO2 inhibition will be an issue.
Another note on esters is when I used to brew on 2hl and 16hl pilot systems and had to flavor match industrial fermentors of 2-3,000hl we had to pull out every trick in the book to be successful. Hydrostatic pressure does have a large impact but almost everything can be compensated with time and effort.
Yeast Health/viability:
Same discussion as my thoughts on ester impact. Only thing I want to add is, a lot of the work and statements on high pressure fermentations are for trials at 7Mpa or even 100Mpa! 7Mpa is 70bar or a ~500 foot fermentor! Not applicable to any brewery in the world (I hope). An excellent resource for this topic (and any deep dive in fermenting) is Brewing Yeast & Fermentation (Boulton and Quain). In this book they cite work done on normally low and high hydrostatic pressures and two different yeasts responded in an opposite way to the same binary conditions. In some typical brewery conditions, the pressure did increase diacetyl and decrease yeast growth and higher alcohols (Arcay-Ledezma & Slaughter). In another brewery conditions experiment (Miedener) the results for higher pressure led to lower head retention, VDK and DMS while some esters doubled. So, I think it is fair to say that relatively large hydrostatic changes could have an impact on your fermentation performance (in many facets) but risky to say with certainty. We also have to remember that these tests we might reference do not prove the relationship for ALL YEASTS!
As with most things in brewing, it is good to be aware of possible risks and then monitor your process and adjust.
Hop character and bitterness:
As far has hydrostatic head (liquid height) impacting hop flavor and bitterness, I have never seen that documented. I understand why it may make sense, that high liquid height means less volatiles are lost but there is an opposite argument. It is well known that tall tanks ferment faster than short tanks driven by the energy that the CO2 bubbles impart into the system (as the rise through the greater liquid column). Could it be possible that the same energy that increases fermentation rate also is able to strip more aroma? Maybe, maybe not. In either case easily adjusted for by the brewer with fermentation changes.
One area to consider in regards to height to diameter ratios and hop character is the brandhefe ring (dried yeast ring above fermenting beer). This ring holds a lot of compounds that are relatively hydrophobic (hop oils and bitterness) and thus can impact sensory. So, if a brewery switches from a short tank to a tall tank (same fill volume) and makes no adjustments then the brandhefe ring will have more surface area relative to the volume and thus we would lose more of the components from the beer. This is easily adjusted for with process changes or process aids like anti-foam. Brewers that want to make consistent beer should strive for consistent brandhefe rings relative to the volume underneath. This is one of the many reasons I never like seeing blow-off barrels receiving yeast on any regular basis.
For whatever direction you decide to go, just be aware of the potential risks, make your purchase choice (keeping in mind the H:D guidance in the Podcast and Jim Larson's Paper) and monitor and manage the results.
Cheers,
Travis Audet
Slant Six Consulting