Bulk Pasteurization Research Thread

[jdubdvdt]

It's been awhile since I was on the forum, but I am back and looking for any insight to come up with a solution for bulk pasteurization. Pappers has a good thread about pasteurization and how to do it on the stove top with bottles. I am including a quote from his post describing the reasonings behind someone wanting to pasteurize. This does not address bulk pasteurization. In this thread, I want to keep it about bulk pasteurization, not about using campden tablets, potassium metabisulfite, or potassium sorbate, or anything else I didn't list. I want to kill the yeast not subdue it.

So, you've made your cider (I keep it simple with juice, ale yeast and pectic enzyme) and have it in the carboy. When fermentation slows down, I start taking gravity readings and tastings. When its at the right level of sweetness/dryness (for me, that's about 1.010- 1.014), rack to bottling bucket with priming solution and bottle. Let the bottles carbonate and condition until the carbonation level is right - for me, that is usually about 1 week but for others it could be sooner. Start opening a bottle every two days or so, until you find that carbonation is at the right level. Warning - if the carbonation level is too high, if you have gushing bottles for example, do not pasteurize, the pressure will be too much for your bottles. Ok, now, we're ready for the point of this thread - pasteurizing.

Why pasteurize? Because at this point, you have a bottle of sparkling cider, with some residual fruit sugar left and yeast that is still working. If you just leave it be, you will likely end up with shrapnel rather than delicious sparkling cider. By gently heating the bottles, you will finish-off our yeast friends - they've done their job, they've performed admirably, but its time to say goodbye. Rather then pasteurize, you could cold-crash, but I don't have the refrigerator space for that and also can't give bottles away to other people using that method. I've found that the sparkling cider is very popular with my friends (and swmbo) and pretty much need to keep a constant pipeline of it going. The good news is its remarkably simple to make and takes much less time than brewing.

Bulk Pasteurization. Some of us that keg and have the necessary equipment might want to stop fermentation at a desired sweetness, backsweeten, or possibly ensure the solution is sanitary. This might be considered "overhandling" but possible unpopular opinion, I think bottling beer an cider feels like overhandling - this is somewhere in between pure kegging and bottling.

Current ideas for bulk pasteurization include:

1. Heat in Brew Kettle
   1. Transfer from fermenter to brew kettle
   2. Heat to 158, hold temperature for 1 minute
   3. Cool.
   4. Transfer to Keg
   5. Flood headspace with CO2 and put in kegerator/keezer for final carbonation.
2. Heat in Keg
   1. Transfer to keg.
   2. Flood headspace with CO2 (CO2 is heavier than Oxygen so oxidation might be limited.
   3. Use sous vide.
   4. Reach 158F for 1 minute.
   5. Flood headspace with CO2 and put in kegerator/keezer for final carbonation.
3. Heat entire Keg
   1. Transfer to keg.
   2. Flood headspace with CO2 (CO2 is heavier than Oxygen so oxidation might be limited.
   3. Spunding Valve might be a good idea here
   4. Heat Brew Kettle with xx gallons of water to 160F
   5. Put entire Keg in Brew Kettle
   6. Hold temperature for xx hours until cider temperature is 158F.
   7. Flood headspace with CO2 and put in kegerator/keezer for final carbonation.

Cons to Method 1:

• May heat unevenly and change the flavor of the cider
• May introduce oxygen post fermentation

Cons to Method 2:

• May damage keg seals, separate rubber feet/handles if older kegs or heat too hot. (this may be a non issue at 158F, thoughts?)

Cons to Method 3:

• May be worse than Method 2 as far as damage keg seals, separate rubber feet/handles if older kegs or heat too hot. (this may be a non issue)

Looking for any other bulk pasteurization ideas, thoughts to tighten up the process, or more pros/cons.
Again I do not want to talk additives, chemicals, or just keeping the keg cold to subdue the yeast. This is about bulk pasteurization.

 

[CKuhns]

I had given bulk pasteurization some thought a while back. I have not done this. I have stuck to bottle pasteurization when I have residual sugar or keg for a dry vs sweet cider. But might be a fun experiment.

If I were to try bulk I would likely try using an immersion heater in a keg. Was thinking a threaded unit. Modifying a keg lid with an appropriate threaded fitting.

There are many heaters on the market. Here is a link to an article with some general information. I would lean towards a laboratory grade unit vs. a less expensive model if I were to do this regularly. But for an experiment may try a less expensive one.
https://www.omega.com/en-us/resources/immersion-heaters

PROs
- A keg could with some modification seal the cider to reduce the chance of oxidation.
- Less likely to damage the keg components than other ways of heating the entire keg.
- By placing the heater in the cider would take less time to achieve desired temp.
- Could purge headspace with CO2 in through the kegs gas port either before sealing, and out through the lid relief or by removing the liquid (out) quick connect and adding a valve.
- valve also could be used to add the thermometer if it would fit in the dip tube and would work after removing the thermometer to transfer the cider to another keg.
- Once complete could add CO2 and a bit of pressure to transfer to a keg for chilling, carbonation (or not if you prefer a "still" cider) and dispensing.
- Very likely a similar cost to a good filter and pump system to remove yeast vs killing them.

CONs
- Cost and complexity due to modifying a keg vs other ways to achieve similar results.
- Ensuring the length of the heating element would need to be completely submerged. (Impossible to see.)
- Would need to add a seperate temperature device to validate the cider achieved the desired temp.
- Some say pasteurization changes the flavor a bit. I personally can not detect a difference when I do it in the bottle.
- With modifications I would dedicate the keg to this acrivity tying up a keg.

Great topic, I am interested to see where this discussion goes.

 

[jdubdvdt]

I had given bulk pasteurization some thought a while back. I have not done this. I have stuck to bottle pasteurization when I have residual sugar or keg for a dry vs sweet cider. But might be a fun experiment.

If I were to try bulk I would likely try using an immersion heater in a keg. Was thinking a threaded unit. Modifying a keg lid with an appropriate threaded fitting.

There are many heaters on the market. Here is a link to an article with some general information. I would lean towards a laboratory grade unit vs. a less expensive model if I were to do this regularly. But for an experiment may try a less expensive one.
https://www.omega.com/en-us/resources/immersion-heaters

PROs
- A keg could with some modification seal the cider to reduce the chance of oxidation.
- Less likely to damage the keg components than other ways of heating the entire keg.
- By placing the heater in the cider would take less time to achieve desired temp.
- Could purge headspace with CO2 in through the kegs gas port either before sealing, and out through the lid relief or by removing the liquid (out) quick connect and adding a valve.
- valve also could be used to add the thermometer if it would fit in the dip tube and would work after removing the thermometer to transfer the cider to another keg.
- Once complete could add CO2 and a bit of pressure to transfer to a keg for chilling, carbonation (or not if you prefer a "still" cider) and dispensing.
- Very likely a similar cost to a good filter and pump system to remove yeast vs killing them.

CONs
- Cost and complexity due to modifying a keg vs other ways to achieve similar results.
- Ensuring the length of the heating element would need to be completely submerged. (Impossible to see.)
- Would need to add a seperate temperature device to validate the cider achieved the desired temp.
- Some say pasteurization changes the flavor a bit. I personally can not detect a difference when I do it in the bottle.
- With modifications I would dedicate the keg to this acrivity tying up a keg.

Great topic, I am interested to see where this discussion goes.

Thanks for the detailed reply, exactly what I am looking for.

I was considering immersion heaters, but I was a little concerned it might burn the cider. I suppose a sous vide directly could burn the cider too. Thoughts?

The other idea I had would be similar to an immersion chiller like a Temp Twister, but it would have to be a lot smaller or you'd never be able to get the keg lid installed/removed.

With an immersion setup like the Temp Twister - you could use a sous vide or other heating methods to heat water in a separate bucket, pump the heated water through the immersion device. It would have to be a lot smaller than the Temp Twister to work in the keg lid. Might be able to get away with a singular run to the bottom and back. Now we are overhandling.

 

[CKuhns]

I would bet a hot water circulation system would certainly be an option.

In essence transfering heat from the hot water to the cider. Again modifying a lid and utilizing a copper or glass coil.

 

[Chalkyt]

Interesting idea!

I pasteurise bottles using a method “inspired” by Pappers post. I guess that you could consider a keg a big bottle, so what I have learned from pasteurising bottles could well apply to kegs but on a larger scale.

Anyhow following is my take on it. I have also attached a paper that I prepared (and posted) a couple of years ago which goes into a lot of detail. You might find it useful.

The Pappers method involves putting the bottles into 80C (176F) water. In the trials that I did, as the bottles heat up, the water cools down and temperature equilibrium occurs around 65C (150F), but of course this depends on the ratio of water to bottles. For me a ratio 4:1 (hot water to bottles) worked. Also, once the bottles are removed from the heat, pasteurising continues until the temperature drops below 60C (140F). The cooldown period generates as much pasteurisation as the heat up period so the conventional target of 30 - 50 pasteurising units for cider is achieved.

So, it wouldn’t be too hard to see what would work if you put a keg of cider into a bath of hot water.

Of course, the size of the keg will affect how quickly the core temperature reaches your target pasteurising temperature, but sticking a cooking thermometer into a keg will soon tell you what works. Although conventional wisdom says that it takes up to 20 minutes for the temperature to stabilise in bottles, a study on computational fluid dynamics by Turnell Corp (just google CFD study) shows that in bottles, it only takes 5 minutes. I guess it would take longer with a keg (depending on its size, of course), but maybe not an unreasonable amount of time.

My method is a bit different to Pappers in that I use a 10L insulated bucket of hot water and a sous-vide heater to hold the temperature at 65C and also circulate the water, so each bottle gets the same treatment for about five minutes or so. This temperature and time also minimises the chance of "cooking" the cider. The bottles go in with a monitoring bottle of water with a cooking thermometer in it. I monitor the temperature and time (I have attached a typical chart of this from a recent batch).

I don’t really need to monitor time and temperature anymore but just do it to “know what is going on”. Consistently the bottles reach 65C (140F) in about 5-7 minutes, and once removed cool down to 60C (140F) in another 5-7 minutes or so This pretty much is determined by the ambient room temperature. There are some studies that suggest yeast (fermentation) will be stopped in a minute or so, but this may not deal with pathogens, so I am happy to stick to 65C and five minutes..

I use the “long” time (it is only just over five minutes) and low temperature for pasteurising as well as keeping carbonation below 2.5 volumes to minimise pressure buildup in the bottles (i.e. this combination generates a maximum of 109psi for a short time, which to me is a reasonable safety margin for "bottle bombs" given that the bottles are rated at well over 200psi).

Andrew Lea has an excellent Carbonation Table which calculates pressure for a given volume of CO2 at a given pasteurising temperature (google Andrew Lea Carbonation Table). At 70C (158F) 2.5 volumes of CO2 would create 122psi, so how well the keg holds pressure may well come into play for you.

I hope some of this helps.

Cheers!

 

[redteam]

Not to distract you from going the heat route, but that one always bothered me, I found this paper https://oeno-one.eu/article/view/2944 on the sterilization of wine musts with a uvc lamp. I cobbled together my own version of it and used it to backsweeten a 1 gallon batch of cider. I plan on using it this fall to sterilize some cider I will press and also use it to halt fermentation when the desired sweetness is hit.

 

[CKuhns]

@redteam I inpressed by the white paper and would be interested in seeing your set up if you were willing to share it?

 

[redteam]

@redteam I inpressed by the white paper and would be interested in seeing your set up if you were willing to share it?

I'm out of town right now, so it's gonna be a few days. But it's all built around sourcing cheap off the shelf stuff. A 25w uvc lamp for aquarium filter, hooked up to an appropriate power supply, then I grabbed one of the quartz tubes for those filters to protect the bulb. The kicker was finding either quartz helical tubes or FEP tubing. UV-C won't pass through glass or normal plastics. Both options have a relatively inexpensive option when sourced on aliexpress, I contacted a mfg that does custom FEP helical tubing and had it shipped to me. It was all sized to fit into 3" abs drainage pipe available at most home improvement stores that I lined with aluminum foil. For my test I also used a very small fluid pump that was claimed to be food grade.

Total cost for me was close to $150 USD, which when balanced against buying an immersion heater that I don't current have. I figured the increased cost was worth it to me.

I plan on setting it up to be used in line between kegs during pressure transfer, without the pump, when I'm ready to use it on a 5 gallon batch to have an oxygen and heat free batch of cider.

I can provide links to the items, I just don't want to post them right away since I'm new and don't want to be accused of shilling something. I've been lurking for awhile and this is something I'm not seeing many others doing and I think it presents an interesting niche solution for sweet cider production that avoids chemical additions(K-metabisulfite) and avoids the concerns of flavors lost with heating.

 

[CKuhns]

Thanks for the great info. Feel free to PM me. If your concerned, although I wouldnt be.