Updated: Mar 10, 2021
A few weeks after you brewed you discover that you made a fantastic brew, but unless you took extensive notes you will not remember the exact details of the temperature levels (and swings) and times during that brewing process.
Ingredients, including water, will vary through time and from batch to batch. The malting and drying processes can vary, this will in turn affect ingredient quality and taste. Ultimately we have no control over that, so let's focus on what we can influence, the process(es).
CONTROL IS KEY
Most electric brewery controllers don't let you pre-program the mashing temps and times and boiling times, or hop insertion times; if you can reliably repeat these time after time, then you stand a chance of repeating the brew. In the first instance I would suggest keeping notes of the times and temperatures, then control to these on the subsequent brews. If you can get a good level of control repeatability (temp and time), then you do stand a chance of perfecting the brew in the long term. If you can't repeat a like for like brew, then you have to look at possibly revamping your control regime to eliminate the possibility of these quality or taste differences being caused by temperature and time variations.
I'd recommend not tweaking the brew until you have done the same one 3 times with little or no variations in the quality or taste. Even the most experienced brewer can struggle to know the full implications of a 'simple' tweak. With an electric brewery control panel you can maintain a repeatable process with little effort during the brew.
FERMENTATION IS ANOTHER KEY
We all know it is really important to keep the fermentation temperatures within 'spec' for the yeast. Brews can be virtually identical up to the point of fermentation, at that point it can go to plan or it can bomb. Fermentation in a garage or shed can be problematic unless it is well insulated. Temperature swings can be considerable. The brew will have a thermal mass, it will start to waver when the environment temperature swings too far for too long. Where possible thermally lag the fermentor and keep it in a room with little temperature swings.
Place a temperature probe on the side of the vessel (or in the wort) and record the temperatures at regular intervals throughout the day. In colder climates pay particular attention to early morning temperatures, if it is low this can imply the room is too cold at night and may need some trace heating. In warmer climates, pay attention to the early evening temperatures, if high this can imply the room is too warm during the day and may need some cooling.