Thursday, July 11, 2013

All about the amazing WinePod Brix sensor

One of the coolest and most useful things about the WinePod is the incredible Brix sensor.   The brains behind the Brix sensor are a semiconductor scientist named Michael Ravkin and an inventor named Tom Lorincz.  Believe me, many people have tried to develop Brix sensors for the commercial wine industry and have failed.  Every year at the Unified Wine and Grape Symposium there is someone with a Brix sensor and then you never see them again.  It is a difficult thing to measure cost effectively  in an opaque liquid with lots of stems, grape skins, and bubbles.   In the commercial wine world, cost effectively probably means for the cost of a new barrel (all commercial winemakers sub-consciously measure everything in a currency I like to call NBs –new barrels)

Brix is simply the % of sugar in grape juice by weight.  We talk about degrees Brix.  1° Brix is 1% sugar by weight.  When wine ferments the yeast turn the sugars primarily into ethanol and CO2.  The WinePod teaching method relies on using Brix to prompt the winemaker to make important decisions.  For example, when the fermentation kicks into high gear, you may need to add nutrients.  Or when it is in decline, we may artificially boost the temperature.  Hitting that window to make a decision can be small -just a few hours.  So Brix is really an important piece of data when making wine.  Of course you can manually measure Brix with a hydrometer, but hydrometers don’t give you continuous data and they don’t send you messages to hurry up and make that final addition.

Density is the weight of the juice per a given volume so it is more general way of talking about Brix.  Water has a density of 1.   So if 100 ml of juice weighs 110 grams, the density is 1.10.   It is 10% heavier than water because the dissolved grape sugars make the liquid more dense than water.   When the wine ferments, it actually drops to below the density of water because alcohol weighs less than water.  

A wine with a Brix of 25° is about the average when we pick grapes.   It has 25% sugar by weight.  It turns out that 25% sugar in water is about 1.1 density.   An average fermentation will start at 25° Brix and end at -2°. Our Brix sensor measures that roughly 10% change and divides it by 25° Brix.   A rule of thumb is that every 1% change in weight is 2.5° Brix.    

So what we just learned is that the weight of your fermenting wine drops about 10% during the fermentation.  In the WinePod, we use this physical change in a very creative way to measure the sugar levels in the grapes.   How do we do this?  We put a float of a known weight and volume in the juice and we continuously measure its weight change wirelessly via magnetic load transfer.  Imagine if you had a water balloon filled with water in a bathtub.  That water balloon wouldn’t sink and it wouldn’t float.  It would be neutral buoyancy.  Now imagine that you start filling your bathtub with big bags of sugar.  The water in the balloon would be less heavy than the sugar water in the tub and it would increasingly float as you add sugar.  Well that is exactly how we measure the amount of sugars in the WinePod.   We measure the change in the weight.  We calculate the weight of a float using magnets.

How accurate is the Brix sensor?  It is usually +/- 1° Brix.  However, when using frozen must, there is a tendency for the dense sugars to fall to the bottom where we measure Brix.  This sometimes will cause the Brix to appear to be much higher (the Sugars are heavier and fall to the bottom).  When the fermentation begins, it all averages out.  So be careful when you are making water additions to understand that the Brix at the bottom of the tank will be higher than the top. 

One more thing about the Brix sensor, like any sensor, it needs to be calibrated from time to time.   There is an easy way to do this.   The Brix sensor was designed to be neutral buoyancy at 35° Brix.  In other words it free floats at 35° Brix.   It is like a balloon filled with 35% sugar by weight.  So if you calibrate at 35° Brix without the float present, it will appear to the sensor to be free floating.  Then you can calibrate 0° Brix with water.  This means you don’t need to calibrate it with real sugar water or juice.   All of this calibration information is provided step by step in the WineCoach software, but now you know the principles of measuring Brix with the amazing WinePod Brix sensor.