I just joined the forum and see numerous questions regarding carbonation issues when bottling. I faced this issue when I first started and got the idea for a means of monitoring the pressure inside my bottles somewhere on the web but I don't remember where. In any case here are two variations on my pressure monitoring system.
In both methods, I use an empty Perrier bottle, a valve, and a pressure gauge to monitor the carbonation progress of a batch of filled bottles. When bottling, I fill my Perrier test bottle when I am halfway through each batch and label it just like the bottles I am filling. I keep a spreadsheet for my batches and can tell when I am approaching bottle bomb territory for each type of bottle (heavy champagne or light beer bottles). If you are interested, I can send you a copy of this spreadsheet (can't attach spreadsheet to this post by forum rules).
In the first method, I mount a tire stem (lots of places on the web to buy these) in the cap and use a tire gauge to measure the pressure. The tire gauge method tends to leak gas when you measure the pressure so you can never be sure that your next measurements match what is happening in your bottles.
A better method is to use the type of rubber valve used in inflatable sports balls like basketballs and footballs and a stem needle mounted in a pressure gauge. The needle and sports ball valve method also loses a little pressure every time you make a measurement but it is very small compared to the tire stem method. You do need to use care and preferable a little glycerin on the needle so you don't puncture the rubber valve when the pressure gets up past 30 psi.
Be sure to keep the pressure bottle with the bottles so it is kept under the same conditions. So, if you put your bottles in a cold storage area, the pressure bottle should go in with them.
Here are a few photos of how I build my pressure bottles and some tips for their use.
Plastic bottle caps have some molding ridges on their inside surface that should be smoothed off with some sandpaper glued to a dowel which is mounted in a drill.
I use a nail to put a small hole in the center of the cap then melt a hole to fit the tire stem or sports ball valve. Use a blade or sandpaper to remove the melted plastic around the hole if necessary.
Add some silicone gasket sealer to the stem or valve then force it through the hole. Give it a quarter turn twist to be sure the silicone is spread evenly. Clean off the excess silicone with a cotton swab wetted with paint thinner. I add more silicone to the top side of the cap if I use a sports ball valve so at low pressure the needle can't push the valve into the bottle. Let the silicone cure overnight.
Use an air compressor or bicycle pump to fill your new test bottles to about 40 psi and put them in the refrigerator. After at least half an hour, remove them from the refrigerator and measure the pressure again. It will be less than 40 psi because the volume of the air in the bottles has decreased with the temperature. This measurement is your base pressure so write it on each bottle with a marker. Leave the bottles overnight and test them the next day. If the pressure has decreased by more than 10%, either you did not tighten the cap enough or your valve installation failed. Write the proven pressure on each bottle with a marker and store it until needed. Discard your failures.
Before you use a test bottle during your bottling operation, squeeze it. If it went soft, throw it away because it leaks. If it seems good, put it in the refrigerator for half and hour and measure the pressure. It should be close (2-4 psi) to the last value written on it. You can't compare the new pressure with the original pressure unless the air in the bottle is at the same temperature so be sure to refrigerate it before your final test.
If your bottle has been pressurized for a week or more and the original and new pressure is more or less the same, this bottle and cap should perform well at least up to the tested value. I recommend using two bottles per batch to make sure they are giving more or less the same pressure. If one lags the other by increasing amounts or flat lines while the other is rising, it has reached its pressure limit and is not reflecting the true pressure in your bottles.
Note that the pressure curve on the spreadsheet starts steep then curves towards a flat line. If you are approaching the failure pressure of the bottle type you used and a projection of the trend will put you into dangerous pressures, put on protective gear particularly eye protection and uncap then recap your bottles. If the first one is a geyser, cool all the bottles in an ice water bath and try again. At the same time relieve the pressure in your test bottle by unscrewing the cap and tightening it back up. What ever you do to your bottles you must do to your test bottle so if you need to cool them when you uncap them be sure to do the same to the test bottle. Make a note on your spreadsheet and keep monitoring until your measurements are stable for at least two weeks. Remember to note the temperature of the place you store your bottles. You can expect the pressure to vary a little bit if the temperature is not constant between measurements.
In both methods, I use an empty Perrier bottle, a valve, and a pressure gauge to monitor the carbonation progress of a batch of filled bottles. When bottling, I fill my Perrier test bottle when I am halfway through each batch and label it just like the bottles I am filling. I keep a spreadsheet for my batches and can tell when I am approaching bottle bomb territory for each type of bottle (heavy champagne or light beer bottles). If you are interested, I can send you a copy of this spreadsheet (can't attach spreadsheet to this post by forum rules).
In the first method, I mount a tire stem (lots of places on the web to buy these) in the cap and use a tire gauge to measure the pressure. The tire gauge method tends to leak gas when you measure the pressure so you can never be sure that your next measurements match what is happening in your bottles.
A better method is to use the type of rubber valve used in inflatable sports balls like basketballs and footballs and a stem needle mounted in a pressure gauge. The needle and sports ball valve method also loses a little pressure every time you make a measurement but it is very small compared to the tire stem method. You do need to use care and preferable a little glycerin on the needle so you don't puncture the rubber valve when the pressure gets up past 30 psi.
Be sure to keep the pressure bottle with the bottles so it is kept under the same conditions. So, if you put your bottles in a cold storage area, the pressure bottle should go in with them.
Here are a few photos of how I build my pressure bottles and some tips for their use.
Plastic bottle caps have some molding ridges on their inside surface that should be smoothed off with some sandpaper glued to a dowel which is mounted in a drill.
I use a nail to put a small hole in the center of the cap then melt a hole to fit the tire stem or sports ball valve. Use a blade or sandpaper to remove the melted plastic around the hole if necessary.
Add some silicone gasket sealer to the stem or valve then force it through the hole. Give it a quarter turn twist to be sure the silicone is spread evenly. Clean off the excess silicone with a cotton swab wetted with paint thinner. I add more silicone to the top side of the cap if I use a sports ball valve so at low pressure the needle can't push the valve into the bottle. Let the silicone cure overnight.
Use an air compressor or bicycle pump to fill your new test bottles to about 40 psi and put them in the refrigerator. After at least half an hour, remove them from the refrigerator and measure the pressure again. It will be less than 40 psi because the volume of the air in the bottles has decreased with the temperature. This measurement is your base pressure so write it on each bottle with a marker. Leave the bottles overnight and test them the next day. If the pressure has decreased by more than 10%, either you did not tighten the cap enough or your valve installation failed. Write the proven pressure on each bottle with a marker and store it until needed. Discard your failures.
Before you use a test bottle during your bottling operation, squeeze it. If it went soft, throw it away because it leaks. If it seems good, put it in the refrigerator for half and hour and measure the pressure. It should be close (2-4 psi) to the last value written on it. You can't compare the new pressure with the original pressure unless the air in the bottle is at the same temperature so be sure to refrigerate it before your final test.
If your bottle has been pressurized for a week or more and the original and new pressure is more or less the same, this bottle and cap should perform well at least up to the tested value. I recommend using two bottles per batch to make sure they are giving more or less the same pressure. If one lags the other by increasing amounts or flat lines while the other is rising, it has reached its pressure limit and is not reflecting the true pressure in your bottles.
Note that the pressure curve on the spreadsheet starts steep then curves towards a flat line. If you are approaching the failure pressure of the bottle type you used and a projection of the trend will put you into dangerous pressures, put on protective gear particularly eye protection and uncap then recap your bottles. If the first one is a geyser, cool all the bottles in an ice water bath and try again. At the same time relieve the pressure in your test bottle by unscrewing the cap and tightening it back up. What ever you do to your bottles you must do to your test bottle so if you need to cool them when you uncap them be sure to do the same to the test bottle. Make a note on your spreadsheet and keep monitoring until your measurements are stable for at least two weeks. Remember to note the temperature of the place you store your bottles. You can expect the pressure to vary a little bit if the temperature is not constant between measurements.
