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Refractometers and mash outs
Dear Mr. Wizard:

Can you give me a formula for converting degrees Brix to specific gravity, or degrees Balling? I have a refractometer and was told that I can check the gravity of my run-off when sparging. It sounds good to me! That way, I wouldn’t have to wait for a hydrometer sample to cool. Also, it would be nice to just take a sample drop to check gravity during fermentation.
Vicky Melius
via e-mail

Mr. Wizard replies: This question raises some issues of semantics that make giving a clear answer difficult without first addressing terminology. In general terms, °Brix, °Plato and °Balling are interchangeable. All three of these scales express the weight percentage of sucrose solutions and relate this weight percentage to specific gravity. The Balling scale is the oldest and is based on Balling’s tables established in 1843. Brix later corrected some calculation errors in the Balling tables and introduced the Brix tables. In the early 1900s Plato and his collaborators made further improvements and along came the Plato tables. Essentially, they are the same, but the tables differ in their conversion from weight percent to specific gravity in the fifth and sixth decimal place of the specific gravity number.  Winemakers, the sugar industry and the juice industry typically use °Brix, continental brewers typically use °Plato, British brewers use specific gravity multiplied by 1000 (for example 1.040 becomes 1040) and American brewers use a mixture of °Balling, °Plato and specific gravity.
I use Plato and specific gravity because my hydrometers indicate   °Plato, and specific gravity is always required when doing brewing calculations. For example, if you multiply  °Plato (expressed in decimal form) by specific gravity, the result is kilograms of extract, a convenient number when doing calculations. Now for the conversion. The following formula shows the conversion from specific gravity to °Plato.

{Plato/(258.6-([Plato/258.2]*227.1)}+1 = Specific gravity

To make sure you are doing your math properly, convert 12° Plato to specific gravity. The correct conversion yields 1.04838.

{12/(258.6-([12/258.2]*227.1)}+1 = SG
{12/(258.6-(0.04648*227.1)}+1 = SG
{12/(258.6-10.5546)}+1 = SG
{12/248.0454}+1 = SG
{0.04838}+1 = 1.04838 = SG

If you have a refractometer, you certainly can use it to determine density. Most refractometers are scaled in terms of °Brix because they are most often used in industries that use the Brix scale. For all practical purposes, you can use the formula above for the conversion. Use caution with your refractometer because light refraction is temperature dependent just like specific gravity. Your sample temperature should ideally be around 68° F. The great thing about a refractometer is that the sample size is small (about 1 mL) and very easy to cool to room temperature before measuring.
I don’t like refractometers for two reasons. The first reason is that they are difficult to read unless they are really high-end. I do like these high-end ones (they resemble a microscope) but they cost $5,000 new! The second reason I don’t like them is that they are not reliable for checking samples from the fermenter because alcohol interferes with the measurement differently than it does with a hydrometer. In other words, a hydrometer measurement on beer may indicate 2° Plato and the refractometer will indicate something different on the same sample. Most brewers express the final gravity as measured by a hydrometer. If you do want to use the refractometer, use it on wort only and then you will be fine.

Dear Mr. Wizard:

If you mash at 156° F for sixty minutes and the mash is fully converted, but you have to leave it at the same temperature for another thirty minutes before you mash out, what effect will that have on your mash?
Gerry Steele
Bloomington, Indiana

Mr. Wizard replies: This is a good question! Mashing at a single temperature above 150° F strongly favors the enzyme alpha-amylase. Alpha-amylase produces a mixture of fermentable and non-fermentable sugars by breaking down the starches amylopectin (branched starch) and amylose (unbranched starch). Starch reacts with iodine to yield a black color and the mash is said to be “converted” when this reaction ceases to occur. Allowing the mash to stand at 156° F after conversion has occurred won’t have any significant impact on the mash. Most commercial brewers will increase the mash temperature to the mash-off temperature after conversion has been confirmed by the iodine test.
Mash time has a more profound effect on wort when the enzyme beta-amylase is active. Beta-amylase produces maltose from starch and is known as the “fermentability enzyme.” Beta-amylase activity is blocked by branches in the molecular structure of amylopectin and leaves partially degraded starch molecules known as beta-limit dextrins. Alpha-amylase, on the other hand, acts differently and can reduce the size of  the beta-limit dextrins. When this occurs, beta-amylase can continue producing maltose. What this means is that alpha-and beta-amylase can work together to produce a highly fermentable wort if the mash rest between 140° F and 150° F is extended. The most effective method to get a really fermentable wort is to increase the mash temperature from 140° F to 150° F over 2 to 3 hours. Some big breweries use this technique to produce light beers with  low residual carbohydrate contents.
What I recommend is that you  get on with the day after confirming conversion. If you mash-off, go ahead and do it, and if not, start wort recirculation.
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