If a recipe calls for using a Campden Tablet a day before pitching the yeast & I don't have any. Can it be successfully & safely substituted with Potassium Metabisulfite ?
Thank You for your time.
Yes, you can! A Campden tablet is simply potassium metabisulphite (or sodium meta, if you buy the older, cheaper kind) compressed into tablet form for ease of measure. You can always use 0.44g of metabisulphite powder in place of the most common size Campden tablet.
OK - one teaspoon (US dry measure) of potassium metabisulphite weighs approximately 1.4 grams. So, 0.44 grams (the contents of one Campden tablet) is 0.44/1.4 = 0.314, or roughly 1/3 of a teaspoon.
While working in teaspoon measure is certainly possible, you'll get much more precise results if you can weigh your materials, since the amount of settling in a teaspoon of any dry crystalline powder can vary the weight by 10% or more. You can get a relatively cheap (under $25) gram scale from places like eBay, and they are far more accurate than working in teaspoons.
Yeah - but the various "rules of thumb" on the use of metabisulphite are hugely different as they are all based on different assumptions, and the actual level of molecular and free SO2 that an addition of metabisulphite produces can vary all over the place, based on the pH of the liquid and the amount of SO2 binding chemicals present in the must. There are several great discussions on sulphite additions in past threads here on Gotmead (some of them are in the Patron's sections), so drill down using the search tool, and become enlightened!
BTW - that one tablet per gallon instruction on your tablets, IMO, adds enough free SO2 to kill a horse in most musts (figuratively speaking). There have been several different sizes of Campden tablets produced over the years since I started brewing - do you happen to know the effective mass (weight in grams) for yours?
Don't know the effective weight, I know from the company that each tablet adds 75 ppm free SO2 per gallon. They are LD Carlson brand and just looking at the package it actually says use 1 to 2 Tablets per Gallon, though I've always just added 1.
ARRGH! Well part of the discrepancy is my memory. I incorrectly recalled the 1.4 gram to tsp relationship, but in fact now that I check my reference sources, 1.4 g of metabisulphite is what 1/4 tsp weighs.
Sorry about that!
Re-doing the calculation, and realizing that 1.4 g per 1/4 tsp translates to 5.6 g per tsp, 5.6 g/tsp / .44 g/tablet means one tsp of metabisulphite powder is roughly equivalent to 12-1/2 tablets (that's for potassium meta, the equivalence for sodium meta is slightly different). That reduces the discrepancy a bit. All these conversions, and my inability to do arithmetic without resorting to a calculator, is one of the reasons why I prefer to work only in grams.
the potassium metabisulfite says
usage 1/8 tsp per gallon = approx 100 ppm of free so2
I have a follow up question.
Is this "potassium metabisulfite" safe to use twice? For example, Before pitching yeast, I use it to kill any possible bugs in the must. When the must has finished sweet, Can I use it again to kill remaining yeast following with sorbate
a few hrs later?
Do keep in mind that several factors (including pH and any compounds that can "bind" the sulphite in your mead), can actually make the actual ppm concentration of free SO2 significantly less than that predicted by the dosage indicated on your meta package. So if I were you I would certainly add an additional 1/8 tsp before sorbate addition, and I might even add another dose prior to bottling if you age this one in bulk for any extended time before getting it into the bottle.
Excellent question mjj, I've been wondering the same thing, I knew that campden tabs are pot meta but had decided that it would just be easier to use the tabs as they supposedly contain the correct amount of it so you don't have to worry about measuring/weighing such tiny amounts(if you want to add to less than a 5 gallon batch for example). I already have the powder and wanted to get some tabs on the last visit to my local LHBS but a new shipment had just arrived and were still buried under alot of other inventory they had not yet had a chance to unpack yet, I think I will get them next visit.
Guys, using powdered KM is very easy even for smaller batches, not even much math is involved. Just dissolve 1/4 tsp in 5 tsp of water, mix to dissolve then use at 1 tsp of your mixture for each gallon. You can dilute it in whatever volume you want just divide it by 5. When doing a bunch of small batches we just make this dilution up before we start and keep using from it, much easier than stopping each time and measuring out little itty bits of KM each time. WVMJ
To expand on wayneb's earlier advice on getting a scale:
Also, my advice is to get a "pocket scale". They are available for under $10 delivered at Amazon and are accurate to 0.1 gram or better. If you really get into this hobby, you will use it literally hundreds of times. Next to a hydrometer, this may be the best bank-for-the-buck investment that you can make.
The trouble with dry measures is that they are not consistent. I've seen tables posted here that show weights for certain dry measure additives. But, for example, the weight of the tablespoon measure does not necessarily equal 6 times the weight of half teaspoon measure (which it should).
Being off a couple of tenths of a gram will most likely not impact your final product. But if you’d like to add things that do not dry measure well, such as many spices (irregularly shaped), a scale in an invaluable tool. The same is true for any ingredient for which cannot find a dry measure to weight conversion.
Get one sooner than later and I guarantee that you will be glad that you did.
Last edited by PitBull; 08-26-2014 at 08:47 AM.
Age improves with mead, even more than mead improves with age.