There seems to have been quite a few questions lately about heat pasteurising and sweet carbonated cider. So, one of my Covid10 lockdown “projects” has been to gather together the various bit of information out there. So, read on if you wish.
Since the great Australian drought and bushfires trashed our small apple crop this year, I have just started making this year’s cider with juice sourced from a commercial orchard. The plan is to bottle some medium sweet carbonated cider with this juice without the worry of losing my own precious juice if things go wrong.
First of all I must declare that none of the following is particularly new or unique, rather I have been able to “stand on the shoulders of giants” (Pappers and all those others who have posted and advised about heat pasteurisation on this forum plus some stuff from “Dr Google”, Andrew Lea and Claude Jolicoeur).
Having done this, I thought it might be worthwhile to post it all in one place here on HBT.
Everyone has different ideas about what carbonation and sweetness they want, but a good starting point suggested by Andrew Lea (Craft Cider Making) is to bottle when the cider is still sweet (say 1.010 or whatever you like), let it carbonate to around 2 atm (which involves letting fermentation continue for about another 0.004), then stop fermentation by heat pasteurisation to end up with a carbonated medium sweet cider.
To get some insight into what happens to the cider, and when, I set up some bottles with carbonated water, pressurised to 2 atm at 20C. (once again, I didn’t want to waste cider if something went wrong!)
We all get concerned about the potential for bottle bombs. So, I used Grolsch type bottles rather than “standard” bottles. Like many, I bottle my cider in 333 ml “standard” bottles as they are a convenient size and easy to get. It was interesting to note that Grolsch bottles are about 20% heavier (typically, 245g vs 195g) so possibly 20% stronger and hopefully able to handle 20% more pressure and thus a bigger “bottle bomb” safety margin.
So, in summary, this is what I found out (much of this, we already know but it might help people just starting out) …
- Bottle internal pressure is a function of pasteurisation temperature which releases CO2 from the cider into the bottle space. The higher the temperature, the higher the pressure and more chance of bottle bombs.
- At the temperature (65C/149F) currently recommended for pasteurising cider, bottles carbonated to 2 atm at room temperature can generate up to 6atm (90psi) of internal pressure (this is exactly what Andrew Lea says, so no surprises here). This is about the practical limit for “standard” beer bottles, although there is some suggestion that they are tested to 100psi before being used in volume production.
- Grolsch type or champagne bottles probably have a 20% or more safety margin over standard beer bottles.
- You can heat pasteurise at anything above 60C (140F) if you leave it for a long enough time. Pasteurisation is unlikely to reliably happen below this temperature. A few degrees make a big difference to how much and how quickly pasteurisation takes place.
- The recommended amount of pasteurisation for cider is defined as 50 pasteurisation units (PUs) which is a function of temperature and time
- Pasteurisation heating time can be in the order of minutes because pasteurisation also continues when the bottles are cooling down.
- The “cooler pasteurisation” method (see posts by JimRausch) is close to the perfect process for home brew cider.
- Controlling the pasteurisation bath temperature with a sous vide heater makes life easy and helps avoid temperatures that might result in bottle bombs.
The details and fine print behind all of this are …
Bottle Pressure vs Temperature
Beer bottles are reputed to be “tested” to 100psi (i.e a bit over 6 atmospheres). So the first step was to heat a bottle carbonated to 2 atm at room temperature and see what pressure is generated at 65C (149F) which is the current “magic number” for pasteurisation.
Wow, at this temperature the pressure got up to 6 atmospheres (90 psi) which is exactly what Andrew Lea (Craft Cider Making) says will happen. This is where I stopped (partly because that is as far as the gauge went and partly because it was getting close to the supposed limit of “standard” bottles, after all I did have a bottle bomb last year when the temperature got away from me).
On this basis it looks as though heat pasteurising in “standard” bottles should be kept at or below starting pressure of 2 atm and pasteurised at 65C or lower. If higher levels of carbonation are required, then using Grolsch or Champagne bottles would be a wise move.
How much pasteurisation do you need?
A bit of background and reference stuff first…
The amount of pasteurisation needed is a bit like “how long is a piece of string”. Commercial operations work on the basis of Pasteurisation Units (PUs) and different operators seem to aim for numbers anywhere between 15 and 45 PUs, either with high temperatures for a short time or lower temperatures for a long time. It seems to depend a bit on what product is being pasteurised and what the yeast or microorganism load might be (e.g. Cider and Beer are different to Fruit Juice.)
Pasteurisation Units are based on work by Del Veccio and others in 1951, who determined that the minimum effective temperature for pasteurisation is 60C, and
1 PU = 60C exposure for 1 minute.
Currently, the accepted amount of pasteurisation for amateur or craft cider makers is in the region of 50 PUs. This comes from a few sources including Andrew Lea, and indirectly from Jolicoeur (149F for 10 minutes). Bembel also has a very detailed post on the subject on this forum (11 May 2016). Therefore 50 PUs seems like a good number to work towards, although some sources claim that 30 PUs is enough.
So, how do you get to the target 50 PUs?
There are time and temperature formulas for calculating the PUs per minute, but if you aren’t a fan of maths here are the PUs per minute for the temperature range that we are concerned with.
(Sorry, just noticed that the table is a bit confusing. In the original version which I wrote in MS Word then pasted here, the PUs line up nicely under the temperatures but when it is saved all the spacing goes away and editing doesn't correct it. You will just have to do the maths or count along the rows, e.g. the fourth temperature 63C lines up with the fourth PUs per minute 2.7 etc.)
Temp C 60 61 62 63 64 65 66 67 68 69 70
PUs per minute 1.0 1.4 1.9 2.7 3.8 5.2 7.3 10.2 14.2 14.2 19.7
(For anyone interested, the commonly used formula is, PU= t x 1.93 raised to the power of (T-60). I also found an article by Andrew Lea which uses the slightly different PU= t x 10 raised to the power of (T-60)/7. In both cases, T = temperature C, and t = time at temperature T in minutes, and both formulae give the same results).
So, what does this mean? To get 50 PUs you simply have to achieve a combination of the PUs at temperatures and times (e.g. 60C for 50 minutes or 70C for 2.5 minutes, or any other combination) that equals 50.
You will see there is a rapid increase in the amount of pasteurisation achieved per minute as temperature increases (but unfortunately for us so does the pressure inside the bottle). This increase in pasteurisation with temperature means that volume processors can use “flash pasteurisation” where the finished product is exposed to a high temperature for a short time during the production process.
The time and temperature combinations that we could safely work with also explain why JimRausch’s “Cooler Pasteurising” method is ideal for those of us without a CO2 setup who are wanting to make sweet carbonated cider while minimising the risk of bottle bombs. Attached are a couple of charts of my results. They both approximate what will happen with a “Cooler Pasteurisation” approach.
The charts take into account the pasteurisation that continues as the bottles cool down towards 60C after they are removed from the bath, so heat doesn’t need to be applied for a long time.
The 65 C Chart shows what happens if the temperature is kept at or below 65C to minimise the chance of bottle bombs (i.e. the pressure should remain below 6 atm). Starting with room temperature (around 18-20C) bottles are pre heated with hot tap water at 50C-60C then the water is heated to 65C. The bottles get up to temperature in 5 minutes. Holding at that temperature for another five minutes results in around 34 PUs. If the hot bottles are removed at this stage (which is around the 10 minute mark) they hold their temperature quite well, taking another 5 minutes to cool down to near 60C. During this time they generate another 15PUs, resulting in just under 50PUs. For me, this was near enough as further cooling will generate a few more PUs.
The 70 C Chart follows the same process but pushes the temperature envelope a bit, minimising the amount of time that bottles need to stay in the bath, but possibly exposing them to a pressure above 6 atm for a short time. This is probably useful if you have a lot of bottles to pasteurise as they only need to stay above 65C for about two minutes. I took the bottles out as soon as their internal temperature looked like reaching 67C (around the 6 minute mark). At his point they had 24 PUs and cooling down generated another 29 PUs resulting in just over 50PUs. (Edit note... the first post had some of these numbers reversed. They have now been corrected... sorry!)
In theory it is possible that a very conservative approach of pasteurising at 62C or 63C for around 25 minutes could also result in good pasteurisation although this is in the region where PUs per minute are quite low, thus opening the process up to a large margin of error and unreliable results.
I used an inexpensive sous vide cooking stick from eBay to control the bath temperature, but simply adding boiling water would work as well (the bath was a fermenting bucket, but a cooler would probably be better). A cooking thermometer in a cork stuck into a bottle of water was used to measure the bottle temperatures, and a pressure gauge attached to a Grolsch cap and carbonated bottle monitored the pressure as temperature increased. I normally use a small plastic drink bottle as well to let me know when carbonation reaches 2 atm (i.e at that pressure the bottle is hard).
I guess you don’t need all of those bits and pieces (but they help you know just what is going on). Just the sous vide heater and a timer allows you to you monitor the process to get good pasteurisation while minimising the chances of bottle bombs.
When starting out making cider it seems that lots of people (me included) are surprised when they don’t produce something like much of the commercial cider (sweet and carbonated). So I hope this exercise has usefully pulled together the forum’s “body of knowledge” about how to produce something that is both sweet and carbonated.
Putting it together certainly kept me entertained for a while.
Cheers!
Since the great Australian drought and bushfires trashed our small apple crop this year, I have just started making this year’s cider with juice sourced from a commercial orchard. The plan is to bottle some medium sweet carbonated cider with this juice without the worry of losing my own precious juice if things go wrong.
First of all I must declare that none of the following is particularly new or unique, rather I have been able to “stand on the shoulders of giants” (Pappers and all those others who have posted and advised about heat pasteurisation on this forum plus some stuff from “Dr Google”, Andrew Lea and Claude Jolicoeur).
Having done this, I thought it might be worthwhile to post it all in one place here on HBT.
Everyone has different ideas about what carbonation and sweetness they want, but a good starting point suggested by Andrew Lea (Craft Cider Making) is to bottle when the cider is still sweet (say 1.010 or whatever you like), let it carbonate to around 2 atm (which involves letting fermentation continue for about another 0.004), then stop fermentation by heat pasteurisation to end up with a carbonated medium sweet cider.
To get some insight into what happens to the cider, and when, I set up some bottles with carbonated water, pressurised to 2 atm at 20C. (once again, I didn’t want to waste cider if something went wrong!)
We all get concerned about the potential for bottle bombs. So, I used Grolsch type bottles rather than “standard” bottles. Like many, I bottle my cider in 333 ml “standard” bottles as they are a convenient size and easy to get. It was interesting to note that Grolsch bottles are about 20% heavier (typically, 245g vs 195g) so possibly 20% stronger and hopefully able to handle 20% more pressure and thus a bigger “bottle bomb” safety margin.
So, in summary, this is what I found out (much of this, we already know but it might help people just starting out) …
- Bottle internal pressure is a function of pasteurisation temperature which releases CO2 from the cider into the bottle space. The higher the temperature, the higher the pressure and more chance of bottle bombs.
- At the temperature (65C/149F) currently recommended for pasteurising cider, bottles carbonated to 2 atm at room temperature can generate up to 6atm (90psi) of internal pressure (this is exactly what Andrew Lea says, so no surprises here). This is about the practical limit for “standard” beer bottles, although there is some suggestion that they are tested to 100psi before being used in volume production.
- Grolsch type or champagne bottles probably have a 20% or more safety margin over standard beer bottles.
- You can heat pasteurise at anything above 60C (140F) if you leave it for a long enough time. Pasteurisation is unlikely to reliably happen below this temperature. A few degrees make a big difference to how much and how quickly pasteurisation takes place.
- The recommended amount of pasteurisation for cider is defined as 50 pasteurisation units (PUs) which is a function of temperature and time
- Pasteurisation heating time can be in the order of minutes because pasteurisation also continues when the bottles are cooling down.
- The “cooler pasteurisation” method (see posts by JimRausch) is close to the perfect process for home brew cider.
- Controlling the pasteurisation bath temperature with a sous vide heater makes life easy and helps avoid temperatures that might result in bottle bombs.
The details and fine print behind all of this are …
Bottle Pressure vs Temperature
Beer bottles are reputed to be “tested” to 100psi (i.e a bit over 6 atmospheres). So the first step was to heat a bottle carbonated to 2 atm at room temperature and see what pressure is generated at 65C (149F) which is the current “magic number” for pasteurisation.
Wow, at this temperature the pressure got up to 6 atmospheres (90 psi) which is exactly what Andrew Lea (Craft Cider Making) says will happen. This is where I stopped (partly because that is as far as the gauge went and partly because it was getting close to the supposed limit of “standard” bottles, after all I did have a bottle bomb last year when the temperature got away from me).
On this basis it looks as though heat pasteurising in “standard” bottles should be kept at or below starting pressure of 2 atm and pasteurised at 65C or lower. If higher levels of carbonation are required, then using Grolsch or Champagne bottles would be a wise move.
How much pasteurisation do you need?
A bit of background and reference stuff first…
The amount of pasteurisation needed is a bit like “how long is a piece of string”. Commercial operations work on the basis of Pasteurisation Units (PUs) and different operators seem to aim for numbers anywhere between 15 and 45 PUs, either with high temperatures for a short time or lower temperatures for a long time. It seems to depend a bit on what product is being pasteurised and what the yeast or microorganism load might be (e.g. Cider and Beer are different to Fruit Juice.)
Pasteurisation Units are based on work by Del Veccio and others in 1951, who determined that the minimum effective temperature for pasteurisation is 60C, and
1 PU = 60C exposure for 1 minute.
Currently, the accepted amount of pasteurisation for amateur or craft cider makers is in the region of 50 PUs. This comes from a few sources including Andrew Lea, and indirectly from Jolicoeur (149F for 10 minutes). Bembel also has a very detailed post on the subject on this forum (11 May 2016). Therefore 50 PUs seems like a good number to work towards, although some sources claim that 30 PUs is enough.
So, how do you get to the target 50 PUs?
There are time and temperature formulas for calculating the PUs per minute, but if you aren’t a fan of maths here are the PUs per minute for the temperature range that we are concerned with.
(Sorry, just noticed that the table is a bit confusing. In the original version which I wrote in MS Word then pasted here, the PUs line up nicely under the temperatures but when it is saved all the spacing goes away and editing doesn't correct it. You will just have to do the maths or count along the rows, e.g. the fourth temperature 63C lines up with the fourth PUs per minute 2.7 etc.)
Temp C 60 61 62 63 64 65 66 67 68 69 70
PUs per minute 1.0 1.4 1.9 2.7 3.8 5.2 7.3 10.2 14.2 14.2 19.7
(For anyone interested, the commonly used formula is, PU= t x 1.93 raised to the power of (T-60). I also found an article by Andrew Lea which uses the slightly different PU= t x 10 raised to the power of (T-60)/7. In both cases, T = temperature C, and t = time at temperature T in minutes, and both formulae give the same results).
So, what does this mean? To get 50 PUs you simply have to achieve a combination of the PUs at temperatures and times (e.g. 60C for 50 minutes or 70C for 2.5 minutes, or any other combination) that equals 50.
You will see there is a rapid increase in the amount of pasteurisation achieved per minute as temperature increases (but unfortunately for us so does the pressure inside the bottle). This increase in pasteurisation with temperature means that volume processors can use “flash pasteurisation” where the finished product is exposed to a high temperature for a short time during the production process.
The time and temperature combinations that we could safely work with also explain why JimRausch’s “Cooler Pasteurising” method is ideal for those of us without a CO2 setup who are wanting to make sweet carbonated cider while minimising the risk of bottle bombs. Attached are a couple of charts of my results. They both approximate what will happen with a “Cooler Pasteurisation” approach.
The charts take into account the pasteurisation that continues as the bottles cool down towards 60C after they are removed from the bath, so heat doesn’t need to be applied for a long time.
The 65 C Chart shows what happens if the temperature is kept at or below 65C to minimise the chance of bottle bombs (i.e. the pressure should remain below 6 atm). Starting with room temperature (around 18-20C) bottles are pre heated with hot tap water at 50C-60C then the water is heated to 65C. The bottles get up to temperature in 5 minutes. Holding at that temperature for another five minutes results in around 34 PUs. If the hot bottles are removed at this stage (which is around the 10 minute mark) they hold their temperature quite well, taking another 5 minutes to cool down to near 60C. During this time they generate another 15PUs, resulting in just under 50PUs. For me, this was near enough as further cooling will generate a few more PUs.
The 70 C Chart follows the same process but pushes the temperature envelope a bit, minimising the amount of time that bottles need to stay in the bath, but possibly exposing them to a pressure above 6 atm for a short time. This is probably useful if you have a lot of bottles to pasteurise as they only need to stay above 65C for about two minutes. I took the bottles out as soon as their internal temperature looked like reaching 67C (around the 6 minute mark). At his point they had 24 PUs and cooling down generated another 29 PUs resulting in just over 50PUs. (Edit note... the first post had some of these numbers reversed. They have now been corrected... sorry!)
In theory it is possible that a very conservative approach of pasteurising at 62C or 63C for around 25 minutes could also result in good pasteurisation although this is in the region where PUs per minute are quite low, thus opening the process up to a large margin of error and unreliable results.
I used an inexpensive sous vide cooking stick from eBay to control the bath temperature, but simply adding boiling water would work as well (the bath was a fermenting bucket, but a cooler would probably be better). A cooking thermometer in a cork stuck into a bottle of water was used to measure the bottle temperatures, and a pressure gauge attached to a Grolsch cap and carbonated bottle monitored the pressure as temperature increased. I normally use a small plastic drink bottle as well to let me know when carbonation reaches 2 atm (i.e at that pressure the bottle is hard).
I guess you don’t need all of those bits and pieces (but they help you know just what is going on). Just the sous vide heater and a timer allows you to you monitor the process to get good pasteurisation while minimising the chances of bottle bombs.
When starting out making cider it seems that lots of people (me included) are surprised when they don’t produce something like much of the commercial cider (sweet and carbonated). So I hope this exercise has usefully pulled together the forum’s “body of knowledge” about how to produce something that is both sweet and carbonated.
Putting it together certainly kept me entertained for a while.
Cheers!
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