Regular readers of the forum will know that I have had a “bee in my bonnet” about heat pasteurizing for sweetness and carbonation control as an alternative to chemical pasteurization. The aim is to bottle cider well above SG 1.000, allow fermentation to continue and generate carbonation to a desired level, then stop fermentation at a point where residual sugar remains… all without creating bottle bombs!
So, thanks to plenty of Covid restriction spare time, and following yet another post asking about heat pasteurization I set up some experimental trials looking at different approaches to heat pasteurizing and recorded what, when and how things happen. It was an interesting exercise, so I thought it worthwhile posting what I have found out even though it repeats some stuff that I have posted before. None of the approaches are new as they are based on previous work by Pappers, JimRausch, Bembel and others, but they each give a different insight into the process.
For craft cidermakers without access to special equipment such as low micron filters or “flash pasteurizers”, heat pasteurizing of bottled cider in a heated waterbath is the easiest and a very effective method of producing sweet, carbonated cider.
The short version of how to heat pasteurize reasonably safely is…
The key issues are:
- Pasteurization occurs at temperatures above 60C and is measured in Pasteurization Units (PUs).
-One PU is the level of pathogens, yeast, etc, destroyed in one minute at 60C for the beverage being pasteurized. So, two minutes exposure will result in twice the PUs.
- The recommended target for heat pasteurizing cider is 50 PUs. The target for other beverages depends on their pathogen and yeast load.
- Pasteurization results from temperature x time. So, lower temperature for a longer time produces similar results to a higher temperature for a shorter time.
- There are opinions that 30 PUs are sufficient to pasteurize cider so in practice, achieving something approaching 50 PUs should result in effective pasteurization.
- The number of PUs generated per minute increases exponentially with temperature so pasteurizing above 65C will produce high levels of pasteurization per minute, resulting in the target of 50 PUs being reached or exceeded in a short period of time.
- Higher temperatures also produce higher bottle pressure which increases exponentially with temperature as CO2 is driven out of solution.
- Depending on the carbonation level, pasteurization temperatures between 65C and 70C can generate bottle pressure in the range 100-160 psi.
- “Standard” bottles in good condition should handle over 160 psi for the short period of time involved in heat pasteurization.
- Bottle pressure generated during pasteurization returns to “normal” (20 psi-40 psi) at room temperature.
- Effective pasteurization can be achieved at temperatures below 70C with a bottle heating time in the order of 10 minutes. Increasing heating time increases total PUs.
- Substantial pasteurization takes place during cooldown as the bottles drop in temperature towards 60C after they have been heated to the pasteurization temperature.
- Achieving well above 50 PUs doesn’t appear to cause flavor changes or pressure problems if excessive temperature isn’t involved.
Two similar approaches are commonly used for waterbath heat pasteurizing.
“High Heat” Waterbath
This is the approach outlined by Pappers (see the sticky at the top of the forum) and JimRausch (see a post on 16 April 2018) where bottles are put in a waterbath which has been heated to 80C or more, then the heat source is removed. When the bottles are put in the bath, they heat up and the water cools down. Generally, equilibrium is reached around 70C (i.e. the bottles and bath reach the same temperature), so bottles don’t reach the initial bath temperature and don’t go above equilibrium.
As pasteurizsation level is significantly influenced by both temperature and time, optional pre-heating of the bottles allows them to reach pasteurizing temperature quickly. This gives the option of short times in the waterbath which in turn minimizes the time the bottles are exposed to high pressure.
“Low Heat” Waterbath
This is the approach outlined by Bembel (post on 11 May 2016) where bottles are put in a waterbath heated to 65C- 70C (or even less) and maintained at that level by stovetop or sous vide heating. The maximum that bottles can reach is limited by the bath temperature.
A file (Cider Heat Pasteurising and Carbonation.pdf) is attached with more background information and detailed results from the trials. Sorry if it is a bit like a College or University assignment. It takes a bit of reading, but does deal with a lot of information for those who want to explore heat pasteurization options.
The idea was to put together enough information so forum members can make decisions about the pasteurization approach that is appropriate for their situation.
So, thanks to plenty of Covid restriction spare time, and following yet another post asking about heat pasteurization I set up some experimental trials looking at different approaches to heat pasteurizing and recorded what, when and how things happen. It was an interesting exercise, so I thought it worthwhile posting what I have found out even though it repeats some stuff that I have posted before. None of the approaches are new as they are based on previous work by Pappers, JimRausch, Bembel and others, but they each give a different insight into the process.
For craft cidermakers without access to special equipment such as low micron filters or “flash pasteurizers”, heat pasteurizing of bottled cider in a heated waterbath is the easiest and a very effective method of producing sweet, carbonated cider.
The short version of how to heat pasteurize reasonably safely is…
Heat pasteurize bottled cider which is carbonated to no more than 3 Volumes of CO2
Do this at no more than 65C-70C for 10-12 minutes then let the bottles cool down
Do this at no more than 65C-70C for 10-12 minutes then let the bottles cool down
The key issues are:
- Pasteurization occurs at temperatures above 60C and is measured in Pasteurization Units (PUs).
-One PU is the level of pathogens, yeast, etc, destroyed in one minute at 60C for the beverage being pasteurized. So, two minutes exposure will result in twice the PUs.
- The recommended target for heat pasteurizing cider is 50 PUs. The target for other beverages depends on their pathogen and yeast load.
- Pasteurization results from temperature x time. So, lower temperature for a longer time produces similar results to a higher temperature for a shorter time.
- There are opinions that 30 PUs are sufficient to pasteurize cider so in practice, achieving something approaching 50 PUs should result in effective pasteurization.
- The number of PUs generated per minute increases exponentially with temperature so pasteurizing above 65C will produce high levels of pasteurization per minute, resulting in the target of 50 PUs being reached or exceeded in a short period of time.
- Higher temperatures also produce higher bottle pressure which increases exponentially with temperature as CO2 is driven out of solution.
- Depending on the carbonation level, pasteurization temperatures between 65C and 70C can generate bottle pressure in the range 100-160 psi.
- “Standard” bottles in good condition should handle over 160 psi for the short period of time involved in heat pasteurization.
- Bottle pressure generated during pasteurization returns to “normal” (20 psi-40 psi) at room temperature.
- Effective pasteurization can be achieved at temperatures below 70C with a bottle heating time in the order of 10 minutes. Increasing heating time increases total PUs.
- Substantial pasteurization takes place during cooldown as the bottles drop in temperature towards 60C after they have been heated to the pasteurization temperature.
- Achieving well above 50 PUs doesn’t appear to cause flavor changes or pressure problems if excessive temperature isn’t involved.
Two similar approaches are commonly used for waterbath heat pasteurizing.
“High Heat” Waterbath
This is the approach outlined by Pappers (see the sticky at the top of the forum) and JimRausch (see a post on 16 April 2018) where bottles are put in a waterbath which has been heated to 80C or more, then the heat source is removed. When the bottles are put in the bath, they heat up and the water cools down. Generally, equilibrium is reached around 70C (i.e. the bottles and bath reach the same temperature), so bottles don’t reach the initial bath temperature and don’t go above equilibrium.
As pasteurizsation level is significantly influenced by both temperature and time, optional pre-heating of the bottles allows them to reach pasteurizing temperature quickly. This gives the option of short times in the waterbath which in turn minimizes the time the bottles are exposed to high pressure.
Waterbath Temperature | Minutes bottles are in the waterbath | Bottle temperature reached | Level of Pasteurization Achieved | Calculated bottle Pressure during Pasteurization @ 3 vols of CO2 |
80C (176F) | 10 | 73C (163F)* | 672 PUs | 11.0 Bar (160 psi) |
82C (180F) | 10 | 71C (160F) | 295 PUs | 10.6 Bar (153 psi) |
80C (176F) | 5 | 70C (158F)* | 175 PUs | 10.3 Bar (152 psi) |
82C (180F) | 6 | 66C (151F) | 59 PUs | 9.4 Bar (137 psi) |
75C (157F) | 10 | 66C (151F) | 49 PUs | 9.4 Bar (137 psi) |
* Bottles pre-heated to 50C
“Low Heat” Waterbath
This is the approach outlined by Bembel (post on 11 May 2016) where bottles are put in a waterbath heated to 65C- 70C (or even less) and maintained at that level by stovetop or sous vide heating. The maximum that bottles can reach is limited by the bath temperature.
Waterbath Temperature | Minutes bottles are in the waterbath | Bottle temperature reached | Level of Pasteurization Achieved | Calculated bottle Pressure during Pasteurization @ 3 vols of CO2 |
70C (158F) | 10 | 67C (153F) | 72 PUs | 9.7 Bar (140 psi) |
67C (153F) | 12 | 65C (149F) | 42 PUs | 9.2 Bar (134 psi) |
65C (149F) | 12 | 64C (147F) | 40 PUs | 9.0 Bar (131 psi) |
A file (Cider Heat Pasteurising and Carbonation.pdf) is attached with more background information and detailed results from the trials. Sorry if it is a bit like a College or University assignment. It takes a bit of reading, but does deal with a lot of information for those who want to explore heat pasteurization options.
The idea was to put together enough information so forum members can make decisions about the pasteurization approach that is appropriate for their situation.
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