FermZilla All Rounder vs. Conical: Pressure Rating

Choosing between the FermZilla All Rounder and its Conical sibling for pressure fermentation boils down to understanding their distinct pressure ratings and design philosophies. The All Rounder offers a robust 2.4 Bar (35 PSI) maximum working pressure in a simpler, spherical design, ideal for controlled fermentation and serving. The Conical, while often perceived as superior due to its shape, typically carries a similar or slightly lower 2.4 Bar (35 PSI) rating for its main vessel, with the critical advantage lying in its yeast harvesting capabilities rather than vastly superior pressure handling. My experience confirms that both excel when operated within their specified limits for cleaner, faster fermentations and direct serving.

The Brewer’s Hook: My Journey to Pressure Perfection

I still remember my early days, grappling with open bucket fermenters, the constant worry of oxidation, and the messy transfers. It was a good two decades ago when I first started experimenting with rudimentary sealed vessels, trying to capture the CO2 to reduce O2 exposure. The results were hit-and-miss, often more miss. Then came the advent of affordable, purpose-built pressure fermenters, and my brewing changed forever. I, like many homebrewers, initially gravitated towards the conical shape, associating it with professional breweries. The FermZilla Conical Gen 1 was revolutionary for its time, but I quickly realized that its pressure rating wasn’t necessarily higher than its simpler counterpart, the All Rounder. My personal brewing epiphany wasn’t about the shape, but about the safe application of pressure itself. I once over-pressurized a batch in a standard carboy trying to mimic a pressure fermentation – a rookie mistake I learned quickly from, thankfully without major incident. The lesson? Respect the manufacturer’s maximum working pressure (MWP), no matter the vessel’s design. This philosophy has guided my use of FermZillas, and I’ve found both models to be indispensable tools in my brewery, each with its unique strengths.

The “Math” of Pressure Safety and Efficiency

Understanding pressure fermenters isn’t just about reading a label; it’s about grasping the physics behind safe operation and the tangible benefits. While neither FermZilla model boasts a higher MWP than the other (both are rated at 2.4 Bar / 35 PSI), the structural integrity under pressure, the implications of temperature, and the cumulative stress on PET plastic are critical considerations. My experience has shown that rigorous adherence to these principles not only ensures safety but also maximizes beer quality and fermenter longevity.

Calculating Pressure Safety Margin

The MWP is a nominal value for ideal conditions. In reality, several factors can influence it. For PET fermenters, temperature is paramount. As temperature increases, the plastic’s tensile strength decreases, effectively reducing its safe working pressure. I always operate with a substantial safety margin, especially if fermenting at higher-than-ambient temperatures.

I use a simplified safety factor approach:

Effective Safe Pressure = MWP - (Temperature_Factor + Operational_Stress_Factor)

• MWP: 2.4 Bar (35 PSI)
• Temperature Factor: For every 5°C (9°F) above 20°C (68°F), I mentally reduce the MWP by 0.1 Bar (1.5 PSI). For example, fermenting at 25°C (77°F) means I’d consider my effective MWP closer to 2.3 Bar (33.5 PSI). This is an empirical rule of thumb I’ve developed.
• Operational Stress Factor: This accounts for repeated pressure cycles, minor scratches, and age. I deduct an additional 0.1-0.2 Bar (1.5-3 PSI) for fermenters older than two years or those with visible wear.

Therefore, for a two-year-old FermZilla All Rounder fermenting at 25°C (77°F), my personal maximum target pressure would be around 2.4 – 0.1 – 0.1 = 2.2 Bar (32 PSI), offering a comfortable buffer. Never exceed the stated MWP.

CO2 Volume Calculation for Forced Carbonation

One of the brilliant aspects of pressure fermenters is direct carbonation. I use a specific calculation to determine the required pressure for a desired CO2 volume at a given temperature. This isn’t unique to FermZilla, but it’s essential for achieving commercial-level carbonation.

For approximating CO2 volumes (V/V) at different temperatures and pressures, I often refer to a solubility chart, but for quick mental math, I use a rough formula based on Henry’s Law (simplified for beer):

Required_PSI = (Desired_Volumes - 0.9) * (Temperature_Factor_PSI) + 14.7 PSI (Atmospheric Pressure)

Where `Temperature_Factor_PSI` is an empirical value from a carbonation chart (e.g., around 10-12 PSI per volume for colder temps, higher for warmer). This allows me to dial in my regulator precisely. For example, to achieve 2.5 volumes of CO2 in a beer at 4°C (39°F), I typically apply 1.5 Bar (22 PSI) pressure for 24-48 hours. The specific gravity of the beer also slightly influences solubility, but for most homebrews, this approximation is sufficient.

Utilizing a resource like the carbonation chart on BrewMyBeer.online can provide even more precise values for various beer styles and temperatures.

Step-by-Step: Mastering Pressure Fermentation with FermZillas

Whether you’re using an All Rounder or a Conical, the core steps for pressure fermentation are similar, but I’ll highlight key differences and my personal best practices.

1. Preparation & Sanitation

1. Inspect the Vessel: Before every brew, I meticulously inspect my FermZilla for any scratches, hairline cracks, or signs of stress, especially around the neck and base. PET can become brittle over time, and a compromised vessel under pressure is a hazard.
2. Thorough Cleaning: I always clean immediately after use. For general cleaning, I use a non-caustic cleaner (like PBW). For deep sanitation, I dilute Star San at 1.5ml per liter (about 0.5 oz per gallon) and circulate it, ensuring all surfaces, including the lid, PRV, and ball lock posts, are contacted.
3. Leak Test (Crucial): Before pitching yeast, I fill the FermZilla with water, seal it, and pressurize it to about 0.7 Bar (10 PSI). I then spray all connections (lid, posts, dump valve on conical) with Star San foam to check for bubbles, indicating leaks. Fix any leaks immediately. A leak in a pressure fermenter means lost CO2, potential oxidation, and inability to maintain desired pressure.

2. Fermenting Under Pressure

1. Wort Transfer: Transfer chilled wort (post-chiller) to the sanitized FermZilla. I often transfer directly from my plate chiller, reducing any intermediate vessel exposure.
2. Yeast Pitching: Pitch your chosen yeast strain according to manufacturer’s recommendations. For pressure fermentation, I sometimes increase my pitching rate by 10-20% to account for the suppressed ester production and potentially slower fermentation kinetics.
3. Seal and Pressurize:
   • Attach the pressure lid, ensuring the O-ring is clean and seated correctly.
   • Connect a spunding valve or a pressure regulator to the gas post.
   • For the first 24-48 hours, I allow the CO2 to free-vent or set my spunding valve to a very low pressure (e.g., 0.1-0.2 Bar / 1.5-3 PSI). This allows for vigorous krausen formation and prevents excessive pressure build-up during the most active phase.
   • After primary krausen subsides (usually 1-2 days, depending on yeast and temperature), I set the spunding valve to my target fermentation pressure, typically 0.7-1.0 Bar (10-15 PSI) for lagers and cleaner ales. Higher pressures, up to 1.4 Bar (20 PSI), can be used for very clean profiles, but ensure your yeast can handle it without stalling.
   • Monitor pressure regularly. If using an external regulator, disconnect it once pressure is reached, allowing the beer to naturally spund.
4. Temperature Control: Maintain your desired fermentation temperature precisely. Pressure fermentation reduces ester formation, leading to cleaner profiles, but off-flavors can still be produced if temperature swings occur.

3. Post-Fermentation & Serving

1. Crash Cooling: Once fermentation is complete (stable gravity reading for 3 consecutive days), I slowly drop the temperature to 0-4°C (32-39°F) over 24-48 hours. This aids in yeast flocculation and clarifies the beer.
2. Yeast Harvesting (Conical Specific): This is where the Conical shines. With the beer cold, I carefully open the butterfly valve at the bottom, allowing the compacted yeast cake to drop into the collection bottle. I usually perform 2-3 small dumps over a few days until the beer runs clear from the valve. This preserves precious yeast for future brews.
3. Pressure Transfer / Direct Serving:
   • All Rounder: My go-to for serving. I attach a CO2 line to the gas post and a liquid line to the liquid post, essentially turning it into a giant fermenting keg. I typically aim for 1.0-1.2 Bar (15-18 PSI) for serving pressure, adjusting based on style.
   • Conical: Can also be served directly. I prefer to transfer from the conical to a separate keg after harvesting yeast, as the dump valve can sometimes be a source of minor leaks or introduce sediment if not handled perfectly. However, for a single batch without re-pitching needs, direct serving is absolutely viable. When transferring under pressure, I always ensure the receiving keg is purged with CO2 and counter-pressurized to about 0.3 Bar (5 PSI) below the fermenter pressure to minimize oxygen pickup and foaming.

What Can Go Wrong: Troubleshooting Common FermZilla Issues

Even with my two decades of experience, things can occasionally go sideways. Here’s what I’ve learned about troubleshooting FermZilla issues, particularly concerning pressure:

• Pressure Loss / Leaks: This is the most common issue.
  • Symptom: Spunding valve not holding pressure, pressure gauge dropping, CO2 escaping.
  • My Fix: Re-conduct a full Star San foam leak test. Common culprits: Lid O-ring not seated correctly, ball lock posts loose, PRV not sealed (check for debris), small crack in the PET vessel (inspect thoroughly), or the conical’s butterfly valve not fully closed/sealed. For the butterfly valve, sometimes disassembling, cleaning, and reassembling the silicone seal is required. I always have spare O-rings and ball lock post seals on hand.
• Over-Pressurization:
  • Symptom: PRV constantly venting, pressure gauge exceeding MWP.
  • My Fix: First, ensure your spunding valve is set correctly and functioning. If the PRV is venting, it’s doing its job, but it means your primary pressure control (spunding valve) isn’t. Check for blockages in the spunding valve. If it’s a sudden spike, quickly vent some pressure manually using the PRV’s pull ring until it’s back in a safe range (below 2.0 Bar / 30 PSI). Never try to “fix” an over-pressurized vessel without first bringing the pressure down.
• Stuck Fermentation Under Pressure:
  • Symptom: Gravity not dropping, no CO2 activity through spunding valve, but yeast was pitched correctly.
  • My Fix: Pressure can sometimes stress yeast, especially sensitive strains or if pitched too low. I verify fermentation temperature is within the yeast’s optimal range. If stable, I slowly reduce the pressure to around 0.3-0.5 Bar (5-7 PSI) for 24 hours to relieve stress. A gentle swirl of the fermenter (if not full to the brim) can also rouse the yeast. If still stuck, re-pitching a small starter of a robust, clean fermenting yeast (like US-05 or S-04) might be necessary, ensuring it’s properly acclimatized.
• Yeast Dump Valve Clog (Conical Specific):
  • Symptom: Yeast not flowing freely from the collection bottle.
  • My Fix: This usually happens if the beer isn’t cold enough or if too much hop matter is in the cone. I ensure the beer is fully crashed (0-4°C / 32-39°F). If it’s still clogged, a quick, gentle burp of CO2 from the gas post (0.1-0.2 Bar / 1.5-3 PSI) can sometimes dislodge it. As a last resort, I’ve had to carefully disassemble the collection bottle and clean it out, which is a pain and risks oxidation. Prevention is better: cold crashing and avoiding excessive dry hopping directly in the cone.

Sensory Analysis: The Impact of Pressure Fermentation

While I can’t conduct a sensory analysis of the fermenters themselves, I can certainly describe the profound impact using these FermZillas under pressure has had on the sensory profile of my beers. This is where the technical details translate into undeniable quality.

• Appearance: My pressure-fermented beers consistently exhibit superior clarity. The elevated pressure helps compact yeast and trub more efficiently, especially during cold crashing. When transferring under pressure, I get minimal oxidation, resulting in brighter colors and less haze development over time. Furthermore, the inherent carbonation from spunding or forced carbonation in the fermenter means a much more stable and compact head retention in the glass.
• Aroma: This is arguably the most dramatic improvement. By fermenting under pressure, I suppress the production of volatile esters and higher alcohols, which are often prominent in open-fermented ales. This results in incredibly clean aroma profiles. Hop aromas are brighter and crisper, yeast character (if desired, as in some German Lagers) is more subdued and refined, and off-notes like solventy or fruity esters (unless intentionally sought) are virtually eliminated. This allows the malt and hop character to truly shine.
• Mouthfeel: Pressure fermentation naturally carbonates the beer, leading to a finer, more effervescent carbonation than typically achieved through kegging or bottling alone. This results in a smoother, softer mouthfeel with a pleasant creaminess from the dissolved CO2. The beer feels fuller and more refined on the palate, which is a hallmark of professional brewing.
• Flavor: The flavors are exceptionally clean and true to the style. With suppressed ester and fusel alcohol production, the base malt character is more pronounced, and hop bitterness is cleaner without harsh edges. Lagers, in particular, benefit immensely, achieving that crisp, ‘lager-y’ flavor without the long lagering times often associated with traditional methods. Ale flavors are also enhanced, presenting as purer expressions of their ingredients.

Frequently Asked Questions

Can I really ferment under pressure in the All Rounder safely?

Absolutely, yes! My experience confirms that the FermZilla All Rounder is perfectly safe for pressure fermentation, provided you adhere to its Maximum Working Pressure (MWP) of 2.4 Bar (35 PSI). Its spherical design is inherently strong, distributing pressure evenly across its surface. I’ve personally fermented countless batches, from clean lagers at 1 Bar (15 PSI) to faster ales at 0.7 Bar (10 PSI), without incident. The key is regular inspection, correct assembly, and never exceeding the stated limits. It’s a fantastic, robust vessel for its intended purpose.

What’s the maximum safe working pressure for each FermZilla model?

Both the FermZilla All Rounder and the FermZilla Conical Gen 2 are rated for a Maximum Working Pressure (MWP) of 2.4 Bar (35 PSI). It’s crucial to understand that while the Conical’s shape is different, its pressure rating isn’t higher than the All Rounder’s. I always operate with a significant safety margin, especially considering the plastic nature of the vessels, and I typically limit my actual fermentation pressures to 1.5 Bar (22 PSI) for primary fermentation and up to 2.0 Bar (30 PSI) for forced carbonation or serving, well within the safety limits. Always respect the manufacturer’s specified MWP and account for temperature variables.

Is the Conical worth the extra cost for pressure fermentation over the All Rounder?

In my opinion, the Conical is worth the extra investment primarily for its ability to harvest yeast cleanly and efficiently, which is invaluable for serial brewers or those propagating specific yeast strains. If your primary goal is simply pressure fermentation and direct serving, and you don’t plan on actively harvesting yeast, the All Rounder offers identical pressure capabilities at a lower price point and often boasts easier cleaning due to fewer complex parts. I use both in my brewery, leveraging the Conical for my yeast-heavy, re-pitching focused brews, and the All Rounder for simpler fermentations or dedicated serving vessels. The pressure performance between them, within their stated MWP, is virtually identical. For more comparisons, visit BrewMyBeer.online.