Imperial Yeast A38 Juice vs. London Fog

Choosing the right yeast for your Hazy IPA is paramount. Imperial Yeast A38 Juice and London Fog, while both excellent for the style, offer distinct fermentation profiles impacting attenuation, haze stability, and ester production. My experience shows Juice tends toward more tropical fruit notes and a slightly lower flocculation, while London Fog often provides a balanced stone fruit character with reliable haze, both thriving in the 19-22°C range.

When I first ventured deep into the murky (and delicious) waters of Hazy IPAs, I made the classic mistake many brewers do: I assumed all “NEIPA yeasts” were created equal. Oh, how wrong I was! My initial batches, while tasty, lacked the precise ester profile and haze stability I craved. I’d oscillate between an overly dry finish and a beer that dropped bright too quickly. It took extensive experimentation, split batches, and meticulous data tracking to truly understand the nuances between strains like Imperial Yeast A38 Juice and the revered London Fog profile. Today, I’m going to share my hard-won insights to help you dial in your next Hazy IPA and avoid those early pitfalls I encountered.

The Brewer’s Math: Pitching Rate & Gravity Impact

Precision in brewing starts with math. For a high-gravity style like a New England IPA, achieving the correct pitching rate is non-negotiable for optimal fermentation and ester production. Too low, and you risk under-attenuation, diacetyl, and off-flavors. Too high, and you can strip away delicate esters. I always aim for a slightly higher rate for NEIPAs compared to traditional ales, typically **0.75 million cells/mL/°P** (Plato) for a typical Hazy IPA.

Manual Calculation Guide for Yeast Pitching

Let’s assume a 20-liter (approx. 5.28-gallon) batch with an Original Gravity (OG) of 1.065, which is roughly 16.1 °P.

1. Calculate Total Cells Needed:
   • Volume (mL) = 20 L * 1000 mL/L = 20,000 mL
   • Degrees Plato (°P) = (OG – 1) * 258.6 * (100 / 258.2) + 18.2 = 16.1 °P (approximate for 1.065 OG)
   • Pitching Rate = 0.75 x 10⁶ cells/mL/°P
   • Total Cells = Volume (mL) * °P * Pitching Rate
     • = 20,000 mL * 16.1 °P * 0.75 x 10⁶ cells/mL/°P
     • = **241.5 x 10⁹ cells** (or 241.5 billion cells)
2. Imperial Yeast Package Comparison:
   • Imperial Yeast packages are typically dosed at 200 billion cells.
   • For my 20L / 1.065 OG batch, I need approximately 241.5 billion cells.
   • This means **one Imperial Yeast package is slightly under-pitched** for this specific scenario. I would typically recommend a starter if I’m targeting the higher end of the pitching rate, or sometimes I’ll simply accept the slight underpitch for a more ester-forward profile, provided my temperature control is impeccable.
   • For London Fog, which often comes in similar cell counts (e.g., Wyeast 1318 or Omega OYL-011), the same calculation applies. The key is knowing your actual cell count per package and adjusting.
3. Gravity Impact (Attenuation):

   The difference in attenuation between A38 Juice (75-80%) and London Fog (70-75%) directly impacts your Final Gravity (FG) and resultant ABV. Let’s use our 1.065 OG example:

   • A38 Juice (assuming 78% attenuation):
     • Fermentable extract = (OG – FG) / (OG – 1)
     • FG = OG – (OG – 1) * Attenuation
     • FG = 1.065 – (1.065 – 1) * 0.78 = 1.065 – 0.065 * 0.78 = 1.065 – 0.0507 = **1.0143**
     • ABV = (OG – FG) * 131.25 = (1.065 – 1.0143) * 131.25 = 0.0507 * 131.25 = **6.66%**
   • London Fog (assuming 73% attenuation):
     • FG = 1.065 – (1.065 – 1) * 0.73 = 1.065 – 0.065 * 0.73 = 1.065 – 0.04745 = **1.01755**
     • ABV = (OG – FG) * 131.25 = (1.065 – 1.01755) * 131.25 = 0.04745 * 131.25 = **6.23%**

   As you can see, even a 5% difference in apparent attenuation can lead to a significant variation in final sweetness and alcohol content, shaping the overall perception of the beer.

Step-by-Step Execution for a Hazy IPA with A38 Juice vs. London Fog

This is my refined process, honed over countless batches, designed to bring out the best in each of these magnificent yeast strains.

1. The Grain Bill: Building the Foundation (Identical for Both)

• My typical base for a 20-liter Hazy IPA:
  • **4.5 kg (9.9 lbs) Pale Malt** (e.g., Maris Otter, Pilsner)
  • **1.0 kg (2.2 lbs) Flaked Oats** (for haze and mouthfeel)
  • **0.75 kg (1.65 lbs) Flaked Wheat** (more haze and protein)
  • **0.25 kg (0.55 lbs) Carapils/Dextrin Malt** (for body and foam stability)
• I aim for a Chloride:Sulfate ratio of **2:1 or 3:1** (e.g., 150 ppm Cl, 75 ppm SO4) to accentuate softness and perceived sweetness.

2. The Mash: Extraction & Fermentability

1. Dough in at **55°C (131°F)** for 10 minutes (protein rest, optional but I find it helps with head retention).
2. Raise to **67°C (152°F)** for 60 minutes. This temperature provides a good balance of fermentable sugars for attenuation and unfermentable dextrins for body and residual sweetness.
3. Mash out at **76°C (169°F)** for 10 minutes.
4. Sparge gently to collect your target pre-boil volume, aiming for a pre-boil gravity of around 1.058-1.060.

3. The Boil: Minimal Bittering, Max Aroma

1. My boil is typically 60 minutes.
2. For bittering, I keep it extremely low. **5-10 IBUs** from a neutral hop (e.g., Magnum) added at 60 minutes. For a 20L batch, this is often just **5g (0.18 oz)** of a 12% AA hop.
3. Flameout/Whirlpool: This is where the magic happens. After chilling to **80°C (176°F)**, I add a significant portion of my aroma hops. For A38 Juice, I love Citra, Mosaic, and Galaxy. For London Fog, I lean into El Dorado, Azacca, and some Comet or Cashmere. I target **2-3g/L (0.25-0.38 oz/gallon)** of combined hops here, steeping for **20-30 minutes**.

4. Fermentation: The Yeast’s Domain

1. Chill wort to your desired pitching temperature:
   • **A38 Juice:** Pitch at **19°C (66°F)**. I let it free rise to **20°C (68°F)** for the first 3-4 days to encourage robust ester production, then hold steady.
   • **London Fog:** Pitch at **20°C (68°F)**. I maintain **21°C (70°F)** throughout the primary fermentation to balance ester production with a clean finish.
2. Oxygenate thoroughly: **1 minute of pure O2 at 1 LPM** for a 20L batch.
3. Pitch your calculated yeast slurry or rehydrated dry yeast.
4. Monitor fermentation closely. Gravity readings should be taken daily after peak activity subsides.

5. Dry Hopping: The Aroma Bomb

This is crucial for both yeasts, but the timing can vary slightly to complement their unique profiles.

1. First Dry Hop (Crash & Carry): When fermentation is about **3-5 points away from FG** (e.g., if target FG is 1.015, dry hop at 1.018-1.020). This allows yeast to biotransform hop compounds. I use **4-5g/L (0.5-0.6 oz/gallon)** here.
   • For A38 Juice, I find this early dry hop particularly potent for unlocking tropical thiols.
   • For London Fog, it contributes to its stone fruit complexity.
2. Second Dry Hop (Post-Fermentation): After FG is stable for 2-3 days, and typically after dropping the temperature slightly to **17-18°C (62-64°F)**, I add the second charge. Another **4-5g/L (0.5-0.6 oz/gallon)**. This preserves brighter, fresher hop aromas.
   • Total dry hop load is often **8-10g/L (1-1.25 oz/gallon)** for a truly hazy, aromatic beer.
3. Contact Time: I typically allow **3-4 days** for each dry hop addition. After that, I crash cool.

6. Cold Crash & Packaging: Locking in the Haze

1. Once dry hopping is complete, crash cool the fermenter aggressively to **1-2°C (34-36°F)** for **24-48 hours**. This helps settle some yeast and hop matter, but critically, it preserves the haze.
2. Package with minimal oxygen exposure. I always purge my kegs multiple times with CO2.
3. Serve after **1-2 weeks** of conditioning in the keg for flavors to meld, but drink fresh! Hazy IPAs are best consumed within 6-8 weeks.

What Can Go Wrong: Troubleshooting Common Issues

Stuck Fermentation

• Cause: Under-pitching, lack of oxygen, nutrient deficiency, or too many unfermentable sugars.
• Fix:
  • Repitch: Add a fresh, active yeast starter.
  • Rouse: Gently swirl the fermenter to resuspend yeast.
  • Increase Temperature: A slight bump in temperature (1-2°C) can sometimes restart a sluggish fermentation.
  • Nutrients: Add yeast nutrients if you suspect a deficiency, especially with high adjunct use.

Lack of Haze or Haze Drop

• Cause: Over-flocculation, insufficient protein in the grain bill, too much cold crashing, or oxidation.
• Fix:
  • Grain Bill: Ensure adequate flaked oats and wheat (my guideline is >25% of the grist).
  • Yeast Selection: A38 Juice is inherently less flocculant, maintaining haze better than some other strains. If using London Fog, don’t cold crash too aggressively or for too long.
  • Dry Hopping: Crucial for haze stability; late dry hopping can help “lock in” haze.
  • Minimize Oxidation: This is paramount. Oxygen destroys haze.

Off-Flavors (Diacetyl, Acetaldehyde)

• Cause: Shortened fermentation, premature cold crashing, or temperature fluctuations.
• Fix:
  • Diacetyl Rest: If gravity readings show fermentation stalled prematurely or if you detect butterscotch notes, raise the temperature to **20-22°C (68-72°F)** for 2-3 days at the end of fermentation.
  • Ferment to Completion: Always ensure FG is stable before moving to cold crashing or packaging.
  • Temperature Control: Maintain stable fermentation temperatures.

Sensory Analysis: Decoding the Yeast Signature

Imperial Yeast A38 Juice

• Appearance: Expect a truly opaque, deep haze. It’s often milky yellow to pale orange, with a persistent, creamy white head that clings to the glass. It tends to hold haze longer than many other strains I’ve worked with.
• Aroma: This is where Juice shines. I consistently get massive tropical fruit notes – ripe mango, juicy pineapple, overripe peach, and often a hint of passionfruit. The esters are forward, bold, and meld seamlessly with hop aromatics. My favorite batches fermented with Juice have an almost “fruit juice” aroma, as the name implies.
• Mouthfeel: Full, soft, and pillowy. It retains a good amount of residual dextrins, contributing to a luscious body without being cloying. The low flocculation contributes to a smooth finish, as less yeast drops out.
• Flavor: Follows the aroma, bursting with tropical fruit flavors. There’s a slight sweetness that balances the bitterness (which is usually minimal). The finish is soft, slightly sweet, and leaves a lingering impression of fruit and fresh hops.

London Fog (e.g., Wyeast 1318, Omega OYL-011)

• Appearance: A reliable, dense haze, typically pale straw to golden yellow. It’s opaque, but I’ve found it can sometimes clarify a *touch* more than Juice over extended periods, though it’s still very hazy. Head retention is excellent.
• Aroma: London Fog typically leans more towards stone fruit esters – distinct peach and apricot, often with notes of tangerine or orange citrus. It’s slightly less aggressive on the tropical spectrum than Juice, offering a more balanced fruit profile that harmonizes beautifully with hop choices like Citra, Mosaic, and El Dorado. It offers a slightly “cleaner” fermentation profile, allowing the hops to speak clearly.
• Mouthfeel: Medium-full, smooth, and creamy. It provides a satisfying body that complements the hop character. While still soft, I sometimes perceive it as having a slightly crisper finish than Juice, owing to its slightly higher attenuation.
• Flavor: A delightful interplay of stone fruit esters and hop character. I find it creates a well-rounded beer, often with a pleasant, lingering bitterness that is quickly subdued by the fruity notes. It tends to finish a little drier than Juice, contributing to its drinkability while maintaining a soft presence.

Frequently Asked Questions

Can I blend Imperial Yeast A38 Juice and London Fog?

While I haven’t extensively explored blending these two exact strains myself, I have successfully blended other NEIPA-friendly yeasts. My advice is to approach it with caution and a clear objective. Blending could offer a hybrid ester profile, but you might sacrifice the distinct characteristics of each. It also makes troubleshooting more complex. If you’re looking for unique ester profiles, I’d suggest adjusting fermentation temperatures or hop schedules first. For more experimental brews, consult resources on BrewMyBeer.online for advanced blending techniques.

Which yeast is better for maximizing hop biotransformation?

Both A38 Juice and London Fog are excellent for biotransformation due to their active enzyme profiles, particularly beta-glucosidases and thiols. In my experience, A38 Juice tends to accentuate the truly exotic, tropical thiol-driven notes more aggressively, giving a “punchier” fruit character. London Fog also performs admirably, often bringing out more citrus and stone fruit complexity from the same hops. The “better” choice depends on the specific hop varietals you’re using and the desired fruit spectrum. For my most “tropical bomb” NEIPAs, I lean towards Juice.

How do these yeasts handle higher ABV NEIPAs (e.g., 8%+)?

Both strains handle higher ABV well, but with nuances. Imperial A38 Juice, with its higher attenuation, can ferment out a bigger beer to a dangerously dry finish if not carefully managed (e.g., higher mash temp, more dextrins). London Fog, with its slightly lower attenuation, often leaves a bit more residual body and sweetness in higher gravity beers, which I find balances the alcohol warmth nicely in stronger brews. Ensure proper oxygenation and nutrient additions for any high-gravity fermentation.