The batch brew dilemma - a few thoughts

The usual complains we hear from coffee professionals about batch brewing in shops are:

1. "They use the Moccamaster (usually the KGBT-741 or another batch brewer designed for home brewing) and the cup quality suffers from that (flat, weak, uneven and overall low extraction that leads to uneven flavor profile)"
The answer here, at least from our experience is:
In vast majority of the home batch brewers, 100%  true. The issue can be hacked a little by using hot water in the tank, but the whole process needs barista's attention for mixing the slurry to achieve more even flow and extraction.

To get the highest possible quality on budget in our small espresso bar, I swiched to manual batch brewing: A V60-03 and later to ETKIN brews with the use of wet WDT. It's easy to do a 60g/L on them and the cup quality is much higher than on cheap batch brewers.
*See "Moccamaster KGBT-741 benchmark" in the last chapter of the post

2. "It sits in the carafe for long, it's getting cold and tastes of metal - not enjoyable."
In one of the lastest Scott Rao posts about batch brewing, he suggests keeping the brew in carafe for 60 minutes and only if the carafe is full (no coffee served from it) in the first 30.

"Flavor degradation is radically different in a full carafe vs the one that had coffee served from it early in the holding process. The air that displaces the served coffee is of room temperature and drops the temperature of the coffee in the carafe. If enough air gets in to drop the temperature below 80°C, the flavor will degrade rapidly." / - Dec 28, 2022 5PM CET: post edited, corrected and quoted according to Scott Rao's comment on our Instagram. Thank you!

When the batch brew sells are slow, solution might be found in immediate slow portion brews that will fill up the carafe and raise the temperature of the brew as the cold air is pushed out (I tried it a few times now, I'll be happy to share our impressions later). So far I am a bit skeptical about how consistent and effective this solution might be.

About the metallic flavor: In my experience, if the carafes are properly cleaned after every brew, there's little to zero indication of flavor alteration (regardless the material - stainless steel/hard plastic). If the carafe is 50-60% full, in 3h the temperature of the brew alters from extremely hot to hot, but drinkable right away. Our personal batch brew quality timer is therefore set to 3:30. After that I taste a little every 15 minutes.

3. "Why would you let it sit there for 4h? Just make less."
That might not be the ideal solution to the problem. How do you decide when to make less? A classic example: Slow or even a busy day in the shop. Almost noone buys batch brew that day. The next day you decide to make a 50% portion and you sell it within 5 minutes. Customers ask for batch brew, you make them wait for it, you sell less, you lose money. Not effective.

4. "Just pour it into the sink after 90 minutes and make a fresh one", said one of our respected colleagues
By all means - if you can afford it, you can do it. On the other hand - the specialty coffee industry talks about values like minimum to no waste almost all the time. In that case, do you too see the irony in pouring great coffee into the sink just because your timer said so?

Moccamaster KGBT-741 benchmark:
When I used a thermometer to measure the temperature of the slurry (I did 5x2 60g/L brews in total in that experiment), the results with just using hot water vs room temperature water were raising my eyebrow.

Room temperature water: 1:00 - 84°C, 1:30 - 85°C, 2:30 - 90°C, 3:30 - 92°C, 4:30 - 93°C (end)
85°C water in the tank: 00:30 - 90°C, 1:30 - 93°C, 2:30 - 93°C, 3:30 - 93°C (end)

Room temperature water: Low slurry temperature for 2 minutes from the 4:30 in total (more than 50% of the total extraction time. Indeed it tasted more flat and weak. Drinkable, but not exciting.
Temperature of the slurry: An ideal range for higher and more even extraction might be sitting between 88 and 94).

85°C water: Slurry hits 93°C at 0:45. Faster flow rate from the hotter water allowed me to grind finer. The cup tasted more interesting with more flavor depth due to overall higher extraction. Note to self: Hotter water than 85 is not recommended - the Moccamaster flow was so agressive that it was messy and it had a tendency to disrupt the bed struture, inreasing the presence of small channels.