Ask The Brewmasters

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We've been producing a raspberry beer with great results for about the past year and all of a sudden in this most recent batch, and to a lesser extent the batch before that, the beer is not clearing up like it normally does.  There is nothing particularly unique about our process...single infusion mash with a grist consisting of 75% pilsner malt and 25% malted wheat, fermented with Sourvisiae.  Post fermentation and diacetyl rest, we dump yeast, crash the beer, add a pectic enzyme, potassium sorbate and potassium metabisulfite and then we add raspberry puree using a diaphragm pump.  After 48 hours we dump the fruit and add Nalco finings.  This process has been consistent with each batch of this beer we have made and up until this point we've always had great results, beautiful red raspberry flavor, aroma and color with great clarity.  This current batch is not clearing up at all with lots of fruit sediment remaining in suspension.  The only thing that has changed with the last two batches is that we recirculated the tank for 20 minutes with the diaphragm pump immediately after fruiting.  Potentially the diaphragm pump is macerating the fruit and causing issues with solids remaining in suspension?  Other than giving it time in the tank with consistent head pressure, does anyone have advice on what I can do to get this sediment to drop out?  I already tried adding more finings, which does not appear to have helped in the least.  I will be leaving the recirculation step out of the process for the next batch to confirm or deny my suspicions that it is the issue.

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I have minimal experience with fruit, but a few things come to mind

• Additional pectin getting released into the beer because of recirculation.
• Fats being released from the raspberries due to recirc.
• Emulsification occurring because of the recirc.

The fact that fruit is remaining in suspension makes me wonder if a level of emulsification occurred. 

One other thought: could it be that the pectin levels in the raspberries was higher this time around? This seems unlikely since it's not just haze, it's sediment remaining in suspension (also, I can only imagine how much more pectin would be needed to make a dramatic shift like this). Even so, I wanted to mention this as a path that might be worth exploring. 

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Nassim Sultan
Beer-talkin' guy & Brewing Consultant
BarrelVision
nassim@barrel.vision
https://barrel.vision
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It is so frustrating when a process has been going great and all of a sudden turns into a headache!

My best guess is that your maceration process changed the pectin extraction and all of a sudden you have a lot more in the beer: pectin comes from the cell walls of the fruit so shredding the fruit can increase extraction. It's also possible this has nothing to do with your process and everything to do with batch-to-batch fruit variation (ugh!). 

If I were in your shoes, here's where I'd start: 

1. Reach out to your fruit supplier and get them thinking about the issue and/or check your raspberry COAs for differences between batches. Your supplier has way more visibility into lot changes, processing metrics, fruit ripeness, etc. Generally, fruit that is less ripe (lower pH and lower Brix on the COA) will have more pectin. Even if they don't end up being helpful in this moment, letting them know about your issue and what you care about (clarity downstream) helps them improve for the future. 
2. Reach out to the supplier of your pectic enzyme. There are different ones on the market that have different properties. There will be an ideal pH and temperature range for yours. Generally, though, these enzymes are not super effective at low temperatures like in a crashed tank or at very low pH ranges (ideal is typically around 4-4.5 pH but check with your supplier). 
3. Check differences in final pH and gravity compared to previous batches. Is it possible that your Sourvisiae kept fermenting after fruit addition with the process change, even with the preservatives? Even if the fruit is the same, as I mentioned, decreased pH can decrease the effectiveness of your pectic enzyme. 
4. This is a bit of a WAG, but I guess it's also possible that you shredded the raspberry seeds and ended up with a tannin haze? I think this is unlikely because you have high levels of protein from the wheat and the two should bind together and drop off, but maybe it's stuck in the pectin and will also need to be addressed? If that's the case, you'll probably be able to taste that the beer is astringent (drying on your tongue) when you sample the tank, vs. a pectin haze will be neutral compared to previous batches or a little sweeter. In the case of tannin haze, you'll need gelatin instead of silica to fine it out. If you don't have gelatin laying around at your brewery, you can test this at the bench with an egg white - if it clears up, this was your issue. 

Good luck, and hopefully the wisdom of the crowd here through MBAA will solve your issue! 

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Jacqueline Beardstrom
Charts & Esters Consulting
Yakima WA
(509) 901-3565
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As you already have macroscopic chunks in suspension, I would not expect finings to be of any help here.  I think it is quite possible that the recalculation through the diaphragm pump could be altering the proteins and creating a buoyant gel, so skipping that step might be your solution in the future.  Our brewery used to make a fruit beer with fermentable extract, and inconsistent mixing of the extract was a problem.  Our solution was to add the extract at high krausen.   The action of fermentation provided good mixing, but it was a process step that required careful timing.

Varying amounts or types of pectin in your fruit extract could also be a source of your troubles.  You might try to start measuring this in your ingredients, and considering ways to control it.  For your current batch: have you considered treating it with pectic enzyme?  You could easily run a lab-scale trial to see if that might be effective.  Also, both the formation of gels and the action of enzymes are pH-dependent, so monitoring the pH of your fermentation might be a good idea.  Since you are fermenting with Sourvicea, you might check Total Acidity as well.  Even if pH and TA are unrelated to your haze problems, they are important flavor components for a fruited sour.

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Cullen Dwyer
Lunenburg MA
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There's already some great info here! Jacqueline has a great point about the pectin potentially having been released, which may be tricky to resolve through pectinase alone because of the low pH (point 2 in that post). Another possibility is that come other pH-sensitive compounds (like proteins) were exposed in the mixing process and the low pH has made them lose some of their ability to sediment (either natural or through the binding to the Nalco).

Separately a slew of polyphenols could also have been released through this process, which can be removed by PVPP, but the finished beer should then be run through a filter to fully remove. 

A couple notes on the Nalco silica finings too, going a bit more in depth on what Cullen brought up:

• Over fining is a risk as well, both with silica-based tank finings and carrageenan kettle finings (though the latter is not likely relevant here). Adding additional Nalco at this point is more likely to contribute to haze, so it is not recommended to add any more to the tank itself. Over-dosing the Nalco will only make the haze more stable and gel-like. At some point it no longer has any proteins to bind to and starts to electrostatically repel itself.
• Instead, run small scale trial to see if there is any benefit to more Nalco. HERE is a finings guide to optimize silica finings, which you can use as the small-scale test to see if there is any benefit to adding more without risking the beer further (full disclosure, it's for our competing product, but the SOP outlined here is applicable to all brands of silica finings).
• There are auxiliary finings that are commonly used in British brewing. They were designed to supplement the action of isinglass finings, but also work with silica finings (after all, the silica finings were originally meant to be vegan alternatives to isinglass). Typically this is used before adding the Nalco, so a small-scale test should again be run to see if it will help pull out any of the new haze, especially if it is being stabilized by excess Nalco.

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Alan Windhausen
Technical Sales Manager
Murphy & Son Inc
Arvada CO
(720) 271-5541
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