Every thread Ive seen on stovetop pasteurizing bottles to kill yeast/stop bottle bombs has involved temperatures of 180-190 F. This seems to have come from cribbing the temperature scheme from milk or apple juice pasteurization, with a fudge factor for poor temperature control.
I work in the food processing industry, and have seen a lot of different methods for pasteurizing beverages (I dont design them though, just help them run). The literature that is usually quoted for milk/apple juice is assuming flash pasteurization I think- raw product comes into a big heat exchanger, is heated up very quickly, and pasteurized product flows out the other side. This is great for people that have a very high degree of control over that process, and who are packaging said product in plastic, which isnt suitable for pasteurizing in bottles.
However, home pasteurizing bottles more closely simulates batch or tunnel pasteurizing- this is what is most commonly done in the beer industry (and many others who are using glass or metal packages). Pasteurizing in bottles presents a new set of concerns: bottle cracking from temperature shocks, and exploding carbonated beverages. Both of these issues can be lessened by lowering the pasteurization temperature.
Pasteurization kills microorganisms through a function of temps of 140 F + and time. Why do we always see temps of 180-190 F in milk/juice pasteurization? Thats because theyre using the High Temperature/Short Time (HTST) type of pasteurization. The alternative to this, which is what is of interest to me here, is a Low Temperature/Long Time (LTLT) process. Equal results can be had with lower temperatures held for a longer time, with the benefit of cracking fewer bottles and possibility avoiding some taste changes in your brew.
(For further reading on how exactly the time/temp function is calculated, look up Pasteurization Units. This page (http://sizes.com/units/pasteurization_unit.htm) is a good start.)
The Method: Pasteurization via Immersion Circulator
Immersion circulators, or sous vide cookers, are becoming more mass produced and cheaper recently. Ive seen them used for mashing on the beer side of things, but I think they are a dream implement for doing LTLT pasteurization at home. They do exactly what youd want a pasteurizer to do- hold a set temperature with a high degree of precision, circulate the water to prevent cold spots, and have an indirect heat source to avoid shattering bottles.
I just did my first trial run of this setup with a batch of Skeeter Pee that I am too impatient to let sit for two weeks to check for signs of refermentation. It went pretty well- I started with heating 4 gallons of water to 140 F on the stove, to reduce the time it took to get the bottles up to temp. Then I took it off the burner, added my bottles and Anova One, and let them sit at 141 F for 15 minutes (clock started after the water temp recovered). The time was based on there being very little yeast left in the clear Pee, so I aimed for about 12 PUs.
Lessons learned: for Petes sake, still wear safety glasses. Closed glass bottles and heat will always pose a risk to your eyeballs. Be careful how you arrange the bottles next to your sous vide unit- I had one that nestled itself right up against the heat source, and it overheated and shattered when I tried to pick it up with tongs.
Overall though, I was encouraged by my low-risk no-carbonation test batch. Im going to do an experiment with a cheapo batch of cider next, to see if I can narrow down how much time is required to kill an active yeast population, and see if I can spot a taste difference between bottles cooked at 140 F and 180 F.
Anyone else tried this yet? Thoughts?
I work in the food processing industry, and have seen a lot of different methods for pasteurizing beverages (I dont design them though, just help them run). The literature that is usually quoted for milk/apple juice is assuming flash pasteurization I think- raw product comes into a big heat exchanger, is heated up very quickly, and pasteurized product flows out the other side. This is great for people that have a very high degree of control over that process, and who are packaging said product in plastic, which isnt suitable for pasteurizing in bottles.
However, home pasteurizing bottles more closely simulates batch or tunnel pasteurizing- this is what is most commonly done in the beer industry (and many others who are using glass or metal packages). Pasteurizing in bottles presents a new set of concerns: bottle cracking from temperature shocks, and exploding carbonated beverages. Both of these issues can be lessened by lowering the pasteurization temperature.
Pasteurization kills microorganisms through a function of temps of 140 F + and time. Why do we always see temps of 180-190 F in milk/juice pasteurization? Thats because theyre using the High Temperature/Short Time (HTST) type of pasteurization. The alternative to this, which is what is of interest to me here, is a Low Temperature/Long Time (LTLT) process. Equal results can be had with lower temperatures held for a longer time, with the benefit of cracking fewer bottles and possibility avoiding some taste changes in your brew.
(For further reading on how exactly the time/temp function is calculated, look up Pasteurization Units. This page (http://sizes.com/units/pasteurization_unit.htm) is a good start.)
The Method: Pasteurization via Immersion Circulator
Immersion circulators, or sous vide cookers, are becoming more mass produced and cheaper recently. Ive seen them used for mashing on the beer side of things, but I think they are a dream implement for doing LTLT pasteurization at home. They do exactly what youd want a pasteurizer to do- hold a set temperature with a high degree of precision, circulate the water to prevent cold spots, and have an indirect heat source to avoid shattering bottles.
I just did my first trial run of this setup with a batch of Skeeter Pee that I am too impatient to let sit for two weeks to check for signs of refermentation. It went pretty well- I started with heating 4 gallons of water to 140 F on the stove, to reduce the time it took to get the bottles up to temp. Then I took it off the burner, added my bottles and Anova One, and let them sit at 141 F for 15 minutes (clock started after the water temp recovered). The time was based on there being very little yeast left in the clear Pee, so I aimed for about 12 PUs.
Lessons learned: for Petes sake, still wear safety glasses. Closed glass bottles and heat will always pose a risk to your eyeballs. Be careful how you arrange the bottles next to your sous vide unit- I had one that nestled itself right up against the heat source, and it overheated and shattered when I tried to pick it up with tongs.
Overall though, I was encouraged by my low-risk no-carbonation test batch. Im going to do an experiment with a cheapo batch of cider next, to see if I can narrow down how much time is required to kill an active yeast population, and see if I can spot a taste difference between bottles cooked at 140 F and 180 F.
Anyone else tried this yet? Thoughts?