I've recently had a few different friends get on the subject of dialing in or making brew recipe adjustments on their automatic drip brewer.  All three coincidentally have the Bonavita TS1900 as recommended in this Buying Coffee Equipment post.  Each had paired it with a proper burr grinder and were buying fresh, quality coffee, but were curious what adjustments may need to be made when using different coffees.  

On this and many other automatic drip brewers there are really only two basic adjustments that can/need to (potentially) be made:  brew ratio, or the proportion of water to coffee which could also be considered brew strength, and grind fineness which will control the flow of water through the coffee and the amount of time it takes for the coffee to be brewed.  

Only having two variables should make it pretty simple and straight forward, however they are not entirely independent of each other, so adjusting one may require an adjustment to the other.  To get started, let's look at what adjusting each variable does in straight forward terms.  

Brew Ratio 

 The ratio of water to coffee or the strength at which you brew will effect the mouthfeel or body of the coffee as well as if it tastes strong or weak or transparent or overly heavy.  Typical brew range is between 1:15 to 1:17, meaning one part or gram coffee to 15-17 parts or grams of water.  I typically start a new coffee at a 1 : 16 ratio, knowing it's easier to go up or down from there.  The lower the ratio, or the less water you use for the same amount of coffee, or the more coffee you use for the same amount of water, the more mouth-filing, substantial, and big or strong the coffee will be.  This can be overdone though; as the ratio is decreased the coffee can loose transparency in flavors, nuance in flavors and aromatics, and become muddled or too thick.  Not all coffees will have a lot of nuanced flavors, but properly roasted, quality coffee should ideally taste and feel balanced or be able to find the sweet spot between luscious and gentle.  

Grind Fineness 

How fine or coarse your grind is will control how quickly the water passes through the coffee (or how long it stays in contact), thus controlling the extraction, or the amount of flavors, aromatics, oils, etc., that are being pulled into the brewed coffee.  Similar to brew ratio, having too high of an extraction can lead to coffee that dry, bitter, or too intense, and extracting too little can lead to coffee that's weak, watery, or bland.  Another way to look at it is that over extraction can result in unpleasant burnt, bitter, charred, and overly roasty flavors (think Starbucks), and under extracted can taste sour, acidic, vegetal, and too in your face, lacking sweetness (think lemons without sugar).  Where it gets tricky is that it's easy to confuse sour and bitter when first learning to taste the coffee to adjust and dial it in to make it as tasty as possible.  

Putting It All Together

The way I started to understand it best was by seeing and reading basically the same principles presented in different ways to increase understanding, so that's what I'm going to do.  Here's where it can get tricky though, since these variables are not independent.  For example, adding more coffee (with the same grind size) can also influence extraction since it will take the water more time to get through the coffee.  I suggest starting with a brew ratio of 1 : 16 and timing the brew and tasting the coffee.  Think about the descriptors noted above and how might you adjust them.  Or, if you're really unsure, buy a bag or two of one kind of coffee and begin brewing batches changing one variable at a time from one extreme to the other to see how it affects the result.  As you learn to identify what needs to be changed and how to change it this will become more intuitive and you may be able to adjust both variables at once.  

A scale to measure your brew ratio will obviously help control that variable by knowing how much coffee and water you're using and using a timer can provide indication to your grind changes.  In general, coffee that is brewing very fast will be less extracted, due to having less contact time with the grounds.  So thinking about this from an if then perspective:  if the coffee tastes burnt, bittier, and/or ashy, chances you need to extract less, or coarsen the grind to speed up the brewing.  Making adjustments and noting how it affects the brew time can also help you learn your grinder to know how significant future adjustments need to be made for faster dial in.  If the coffee tasted too sour or acidic, I would make the grind finer to slow down the extraction to balance it out and brew sweeter coffee.  If the coffee tasted really weak and watery and sour, you may need to add coffee or strengthen your brew ratio and grind finer. 

For those that like the visual representation, I like to refer to Barista Hustle's excellent Coffee Compass.  

The Coffee Compass is certainly very comprehensive, and can be a bit overwhelming, but if you take the time to work through it, you will start to understand what you're doing and why and really learn how to quickly and effectively dial in a coffee to make it taste as good as possible.  Many of these basic principles carry over to all types of brewing, including espresso, as detailed in this past improving espresso post.  To sum it up, and over simplify it think of this:

If it's sour grind finer and increase the brew time.

If it's bitter, grind coarser to decrease the brew time.

If it's too bold and you can't taste any specific flavors (and you're supposed to be able to), decease the amount of coffee or increase the amount of water

If it's too weak, watery, or thin, increase the amount of coffee or decrease the amount of water.

If you have any questions, please reach out or leave a comment below, and I hope this helps provide a better understanding of how to make tasty coffee at home.  This post is not the end all be all by any means, but if it's all you do to try and make the most out of your equipment and coffee, you should be able to make some great coffee.  Thanks for reading.