Double boiler: How long to heat to 160?

[MtnGoatJoe]

So, last year, I heat pasteurized my still cider in pots on my stove. It was quite a process because I didn't want to boil the juice.

My thought this year is to use a double-boiler. Does anyone have any idea how long it would take a 20 quart double boiler to reach 160 degrees? Or should I shoot for a lower temp at a longer time?

20 quart double boilers are kinda pricy, and I'm hoping someone can provide me an assurance this would work before I place my order.

Thanks!

 

[Chalkyt]

Unfortunately I don't think that anyone can give you a standard answer as it is all a case of "suck it and see", since the time depends on your heat source, starting temperature of the water, etc.

The "lower temperature for a longer time" approach is worth looking at. There is a post by Bembel (May 11, 2016) that addresses time and temperature needed for pasteurisation. Conventional wisdom says that pasteurisation starts at 140F (60C) and at this temperature the bottles will need to be held for 50 minutes to reach 50 pasteurisation units (PUs) which is the conventional target. However there are views that 30 PUs is fine for cider, and a recent 2020 Washington State University paper suggests that even a few minutes at 140F will reduce high populations of spoilage yeasts.

As far as "how to do it" is concerned, the technicalities are...

Pasteurisation per minute increases exponentially with temperature, so to give you an idea of this effect, at 145F (63C), 20 minutes heat exposure is needed to reach 50PUs but at 150F (66C) only 5 minutes of heat exposure is needed. At 158F (70C), less than 2 minutes are needed. So it is a matter of doing the time and temperature maths for del Veccio's pasteurisation formula in order to achieve the pasteurisation level that you want.

As a guide, I put my room temperature bottles in a constant 147F (65C) waterbath for 10 minutes, by which time the contents have reached the target 147F (65C), then remove them. They achieve up to30 PUs as their temperature increases above 140F (60C) in the waterbath, then another 20 PUs or so after they are removed and cool down to 140F (60C). I really am not fussed about the actual PUs achieved as long as it is likely that the time and temperature combination will result in something approaching 50PUs. It is just a matter of understanding the process. Even with carbonated cider at 2.5 volumes of CO2, these temperatures shouldn't increase the bottle pressure much above 100psi which is well below the recognised minimum 130psi standard for recycled beer.

Both Pappers method (top of the forum) and Jim Rausch's "cooler" method (16 April 2018) achieve similar results. I haven't experienced any "cooking" of the cider at these temperatures.

Hope this helps.

 

[MtnGoatJoe]

Unfortunately I don't think that anyone can give you a standard answer as it is all a case of "suck it and see", since the time depends on your heat source, starting temperature of the water, etc.

I should have mentioned that I'm going to force carbonate most of the batch, so it's just juice in a pot that needs to heat up.

Last season, I heated the juice in a pot on the stove, and it took a LONG time to heat up because I kept the burner low (so I wouldn't boil the juice).

I'm hoping that a double boiler will be faster since it will be heating at "max" temperature. We'll see. I might just have to bite the bullet and order the pot and see how it goes.

And yes, I've been reading the pasteurization thread and may end up using a lower (and longer) temp if it takes too long to get to 160.

 

[MtnGoatJoe]

Ok, so just to followup...

Reminder: I'm just pasteurizing juice in a pot, not bottled cider. I may do bottle pasteurizing eventually, but I have a 128 oz uKeg, and a 64 oz uKeg to force carbonate. And the reason I'm using a double boiler is to prevent boiling AND reach 160 degrees as quick as possible. Anyway...

I bought a 16 qt double boiler on Amazon for $93. I put a gallon of water in the bottom pot, and 3 gallons of water in the top. I could probably fit a little more in the top, but 3 gallons is a nice even number, and I'm worried the pot might spill when I move it off the burner.

The starting temp of the tap water was 61 degrees. It took 46 minutes to heat water to 160 degrees with the stove set to 8 (out of 9). A few bubbles formed on the bottom and sides in the top pot, but there was no boiling.

As soon as it hit 160 degrees, I moved it off the burner. The temp continued to climb to 164 degrees after 7 more minutes, and was still at 164 degrees after 10 minutes. From everything I've read, I consider this pasteurized. From Chalkyt's post above, it sounds like this is a bit overkill, so I may look at pasteurizing at a lower temp later. Right now, 10 minutes at 160 degrees is my comfort zone.

Also, with the thermometer attached, the lid didn't close. I don't know how much this slowed down the process, but I might look at drilling a hole in the lid for the temperature probe. Even if it's not faster, it will certainly be more convinient.

 

[Chalkyt]

I can't find the link to this paper from WSU. It was in a reply to one of my posts earlier this year (I think), but I can't remember who posted it. Nevertheless it might help you zero in on the time and temperature you need.
Cheers!