Food Science B

[ndkuma01]

Water activity is the amount of "free" water in a food. It's useful for determining food safety as spoilage bacteria can only live on foods above a certain water activity. The symbol for water activity is a_w.
To determine the water activity of a food, say a pickle, you would
Take the mass of the food (Initial Mass)
Put the food in a plastic bag and squish it as much as you can
Cut a small hole in the corner of the bag and drain out the liquid
Measure the mass of the remaining pulp (Final Mass)
Then, to calculate the water activity, use the equation (Initial Mass - Final Mass)/(Initial Mass)*100.

Thank you so much!

[trehank]

Does anyone have any clue on how to determine the pH of a pickle and determine the moisture besides dehydration? Also besides the FDA, does anyone have any other resources that I could use?

[SPP SciO]

Does anyone have any clue on how to determine the pH of a pickle and determine the moisture besides dehydration? Also besides the FDA, does anyone have any other resources that I could use?

Indicator paper will show the pH of a pickle if you test some liquid squeezed from it. Moisture can really only be determined by measuring mass before and after removing the water. As noted above, students have been asked to do this manually at competition - mash a pickle as much as possible in a plastic bag, let this run into the corner of a bag, and then cut a hole to drain it out. I am curious to see how this compares to oven dehydration. The pickle pulp would still feel wet so there’s definitely some margin of error.

Khan Academy has a lot of videos on the chemistry of fermentation, but I find it can be pretty advanced for most middle schoolers. Still a good resource if you’re familiar with some basic chemistry.

[trehank]

Thank you so much

[dvegadvol]

The pickle smooshing "experiment" has to be one of the worst designed ever. A cucumber is > 90% water by weight. There's no way we'd ever get close to that number. I've also seen a definition of moisture as "everything which evaporates upon heating". We won't get close to that number either. What are we supposed to "smoosh" the pickle with? There's no listing for a rolling pin or other suitable equipment...

[DragonTownEpic]

The pickle smooshing "experiment" has to be one of the worst designed ever. A cucumber is > 90% water by weight. There's no way we'd ever get close to that number. I've also seen a definition of moisture as "everything which evaporates upon heating". We won't get close to that number either. What are we supposed to "smoosh" the pickle with? There's no listing for a rolling pin or other suitable equipment...

I agree, the experiment is pretty sketchy. The event supervisor should provite the equipment, but apparently that may not be the case.

[Advith9]

Do you know if an outlet will be provided at a regional and state contest? Me and my partner are building a digital salinometer and it needs a plug. I could replace it with a battery, but I'm not confident about that.

[gz839918]

Do you know if an outlet will be provided at a regional and state contest? Me and my partner are building a digital salinometer and it needs a plug. I could replace it with a battery, but I'm not confident about that.

Event supervisors aren't required to let you use an outlet because the rules don't comment on it, so it's safer to assume that you won't have access to one. Most electrical salinometers won't require a lot of power input, so a small battery (or several batteries combined in series, and maybe a voltage regulator if you need it) should be enough. If you really want to be sure you have an outlet, you can ask for a clarification on SO Inc., or you could email your regional and state director. Hope that helps!

[Mish...]

I remember I went to Churchill invitational and most of the teams were using the orange salinometer or almost store bought salinometer. If anyone could share anything they know about this salinometer or how your team made your salinometer? Thanks in advance.

[DragonTownEpic]

I don't think a store-bought salinometer is allowed. Our salinometer is a plastic pipette with modeling clay stuck onto the bulb. We drew lines on the skinny part corresponding to the water level for salt percentages from 1-10%. It's helpful to make the clay flat, as that allows the salinometer to be used in shallower solutions.