When we drink, our minds get confused and foggy. That's because alcohol affects the brain and central nervous system. It's not possible to go into the brain and measure how much alcohol is present. But it's easy enough to get a blood sample, which gives a very good estimate of the level of alcohol throughout the body.
Evidence shows a direct correlation between blood alcohol and alcohol in the brain.
Let's take a look at the process by starting with the alcohol itself. Wine, beer and hard liquor all contain alcohol, or more specifically, ethanol. In the fermentation process that produces beer and wine, enzymes found in yeast are used to break sugars down into ethanol, a smaller and simpler chemical. Although our human chemistry allows us to metabolize sugars in much the same way as yeast cells, we can't form alcohol during this process because we lack the crucial enzymes present in the lowly yeast. Alcohol content varies among drinks.