Salinity meter

[_john]

I'm interested in buying a salinity meter after reading about it in Modernist Cuisine (volume 3 page 158) and its use in equilibrium brining. MC says they are "inexpensive" so I thought of buying one.

What is the important range to be measured? Can I use a multimeter and a calculation? And most importantly what models (of strand alone salinity meters) do you recommend?

[emannths]

If you bought one of the $15-20 salinity/TDS meters from Amazon (example), you could just use serial dilutions to confirm your salinity is in the right ballpark. Most only go up to about 10,0000ppm = 1%. Dilute your brine 10x and you'll be able to use it.

You could try using a multimeter, but it's probably more trouble than it's worth. Probe composition and separation, container size, etc can all throw off the measurement.

[fledflew]

I have a bit of experience with salinity meters (what works, what doesn't, accuracy, ease of use, etc) as a result of an aquarium hobby (obsession). Unfortunately, I do not have a copy of Modernist Cuisine. Does the book detail any specific type of instrument? Could you elaborate on the equilibrium brining technique? The google search returns a brief interview with Nathan mentioning that it involved a longer soak in a less concentrated solution, but not much more. I should be able to point you in the right direction (equipment-wise) if I can understand the technique a little bit more and figure out what is trying to be accomplished.

[_john]

@fledfew As far as I understand it the equilibrium brining technique works by taking some meat, say 100g, an equal weight of water, 100g, and adding twice the percentage of salt to the water as you want the final percentage of the meat to be. 100g (minus bones) of beef + 100g or water + 4g salt + time = 2% brined beef. The salnity meter is used to measure the brine over time to determine when it has equalized (reached 2% in the example above).

@emannths I don't think I need the precision of a ppm meter as it would mean that I would have to dilute some of the remaining brine every day to check it. But then again maybe this is the only type of meter available?

[fledflew]

Okay, I understand the premise of equilibrium brining now. Thank you. There are a couple different types of devices that I'm familiar with that can perform the measurements you are looking for. Salinity is measured (in the aquarium world) using specific gravity. SG is a weight measurement - a gallon of salted water will weigh more than a gallon of distilled water. This measurement varies because water expands and contracts with fluxuations in temperature so a gallon is not always a gallon. Parts per thousand (PPT) is a constant, in that 50 grams of salt dissolved in 1000 grams of water (5%) will always have the same ratio of salt and water. There are conversion charts based on water temperature that are available, but we will skip that for the time being.

The first device is a refractometer. It is a cylinder about 6-8 inches in length and maybe an inch in diameter. On one end, there is a "slide" or "plate" about 1/2" by 1" that has a hinged cover. You lift the hinged cover, put a few drops of the tank water (or brine in this case) onto the lens, flip the cover back down over the water, hold it up to the light and look through the lens on the opposite end of the cylinder. Within the eyepiece, there is a scale that will indicate the SG/PPT. It works by utilizing a prism inside the device that breaks down the incoming light shining through the water, measuring the amount of refraction. Most models out there now are temperature compensating, so there is no need for any conversion charts. I'm not sure what the functional range of the temperature compensation is, though. The documentation available online doesn't indicate a range either. Presumably, the brine that you will be testing is at about 37 degrees F. Since you're only testing a few drops of water, it should come up to a usable temperature in a matter of seconds. These devices are extremely accurate and do not require any batteries. The downside is that you need to remove a couple drops of the brine every time you want to take a measurement - presumably daily? Also, if the device is dropped onto a hard kitchen floor, it could be the end of the refractometer. The model that I've had for close to 15 years is the Captive Purity available here. At the time, it was the only model available and cost over twice as much. There are several other manufacturers and online stores to get them at for much cheaper these days.

The other device that would suit your needs is a salinity meter like this one. I believe that it measures the conductivity of the liquid to get its readings. I've seen these in use on other aquariums, but I do not have one myself. It may be possible to drop the probe into the brine and then run the lead outside the fridge (maybe using a magnet to hold the base to the outside of the fridge). The user's manual states that the temperature compensation range is 32-122 degrees F. The downside of these are that they're not waterproof and require batteries. Also, the electrode that is on the probe could corrode if left in a salt solution for prolonged periods. There are also handheld pen style salinity meters available. Most of them that I found measure total dissolved solids (TDS), so the addition of things other than salt (such as sugar) might throw your measurements off. In fact, I believe that the addition of sugar to a brine would throw off any of the devices that I've mentioned, although we could easily calculate and compensate for that. If you went this route, I'd opt for a waterproof model.

All in all, I'd recommend the handheld refractometer for your needs because of its ease of use, precision, and the fact that it doesn't need batteries.

Steer clear of any mechanical instruments. I once lined up 4 of the identical model, put the same salt water sample in all four, and received 4 different readings.

Sorry for the long winded answer, and I hope that this information helps.

[haresfur]

I know a bit about salinity measurements but haven't used them for food. Salinity meters measure the electrical conductivity of the solution and conductivity is just 1/resistivity. The units are typically microSiemens/cm which used to be called micro-mhos/cm: mho = backwards ohm, ha ha. Most meters will then use a general calculation to convert to salinity.

The difference between resistivity and resistance is the distance component. The resistance between 2 probes 1/2 cm apart will be less than 2 probes 1 cm apart. The size of the probes will also make a difference when measuring solutions.

Temperature affects the conductivity of solutions so all but the really cheap instruments will be compensated for temperature.

So in theory you could use an ohm meter if it measures the right range of resistance. But you need to keep a consistent geometry on the probe and preferably platinum plated electrodes. Then you would need to calibrate at the temperature you would be using unless relative numbers are ok. With cheap electrical devices these days, I'm not sure it's worth the trouble.

[_john]

Thanks for all the information. I will report back when I make a purchase.

[Shalmanese]

You might also run into problems if the natural proteins that leach from the meat affect conductivity. As a test, I'd put a piece of meat in pure water for 24 hours and see what any salinity meter measures to figure out if that's going to be a problem.

[boilsover]

Thermoworks sells one that is not too expensive.